PLATO
(428/427 BCE–337/336 BCE)

The philosopher Plato was born to an aristocratic Athenian family. His father Ariston was said to be descended from the legendary King Codrus; the family of his mother Perictione was prominent in more historical times. Dropides, an ancestor of Perictione, was a relative and friend of Solon (as Plato himself reports in the Timaeus, 20e). After Plato's father's death, Perictione was remarried to Pyrilampes, a political associate of Pericles and Athenian ambassador to the Persian king. Perictione's brother Charmides and her cousin Critias had a more sinister career, as members (and in Critias's case, ringleader) of the Thirty Tyrants who ruled Athens in a bloody junta, after the defeat by Sparta in 404 BCE.

Plato's family is well represented in the dialogues, perhaps to compensate for his own absence. In the Charmides, situated thirty years before the rule of the Thirty, Plato introduces his uncle Charmides as a promising young nobleman, under the influence of his older cousin Critias. The reference here to Charmides' family allows Plato to sing the praises of his own household, as the union of two outstanding families "than which no more noble union can be found in Athens" (Charmides 157e). The two families in question are those of Perictione and Pyrilampes, Plato's mother and stepfather. It is Plato's cousin Critias the tyrant (and not, as some scholars have supposed, the tyrant's grandfather) who appears again as introductory speaker in the Timaeus and as narrator in the unfinished Critias. Plato's older brothers Glaucon and Adeimantus are the chief interlocutors in the Republic, his stepbrother Demos is mentioned as a reigning young beauty in the Gorgias (481d), and his half brother Antiphon appears in the Parmenides as the one who preserves the memory of the philosophical conversation between Socrates, Zeno, and Parmenides. Plato had no occasion to mention his sister Potone, the mother of his nephew Speusippus who succeeded him as head of the Academy.

We are largely dependent on the autobiographical sections of the Seventh Letter for information about Plato's life. (The authenticity of this Letter is disputed, but even scholars who doubt its authenticity generally assume that the author was well informed.) The author of the Letter reports that Plato's relatives in the anti-democratic coup of 404 BCE invited him to join them, and that he, as an upper-class young man of twenty-three with political ambitions, was initially sympathetic; he expected these men to lead the city "from a life of injustice to a just government." But Plato observed that in a short time "they made the previous (democratic) regime look like a Golden Age" (Epist. VII, 324d). Thus Plato was repulsed by the behavior of Critias and the oligarchs; on the contrary, he admired the courage of Socrates in refusing to obey the tyrants' command, when they ordered him to lead a death squad against a prominent democrat. Plato's political ambitions revived in the restored democracy after 403, but after watching the politics of Athens for ten or fifteen years he concluded that the situation was hopeless, and that "the races of mankind would not cease from evils until the class of true philosophers come to political power or the rulers of the cities practice true philosophy" (Epist. VII 326b). At the age of about forty, Plato then departed for the Greek cities of southern Italy and Sicily.

Sometime after his return to Athens from Syracuse (c. 387 BCE), Plato began to gather together the group of students and researchers in science, mathematics and philosophy that became known as the school of the Academy. The early fourth century saw the creation in Athens of the first fixed schools of higher education, replacing the wandering Sophists of the fifth century. Antisthenes, the follower of Socrates, and the famous orator Isocrates had both recently established their schools. Unlike these institutions, Plato's community of scholars seems to have had no formally enrolled students and no tuition fees.

We know very little about the functioning of the Academy. The physical basis was a small estate with a garden owned by Plato, in the suburban neighborhood named after a park and gymnasium dedicated to the hero Academos. Formal instruction was probably offered in the gymnasium; the communal meals, or syssitia, presumably took place in Plato's villa. We happen to know of one public lecture given by Plato "On the Good." There is no evidence for a curriculum in mathematics and dialectic modeled on the studies of the guardians in Republic VII, as some scholars have supposed. There is in fact no evidence for any fixed curriculum. The only contemporary report (other than veiled attacks from Isocrates as head of the rival school) consists of quotations from Attic comedy, which make fun of the haughty manners and elegant dress of intellectuals from the Academy, and of their elaborate pedantry in the botanical classification of a pumpkin.

The intellectual caliber of the school is attested by the quality of its associates: on the one hand, Aristotle, who worked in the Academy for twenty years before Plato's death, and on the other hand Eudoxus, a great mathematician and astronomer, who seems to have maintained close contact with the school over many years, despite philosophical disagreement with Plato on central issues. Clearly, the members of the Academy were as much concerned with ethics and politics as with science and theoretical philosophy; the school is sometimes represented as a training program for statesmen. Plato's personal prestige is reflected in Aristotle's elegy to Friendship, where Plato is called "a man whom the bad do not even have the right to praise, who alone or who first among mortals clearly showed, in his own life as in his teachings, that to become good is also to become happy (eudaimôn )."

Plato's quiet life in the Academy was interrupted in 367 and 361 by two invited voyages to the court of Dionysius II in Syracuse. Plato was persuaded to accept the invitation by his close friend Dion, the uncle of the tyrant, whom Plato had converted to philosophy on his first visit to Syracuse some twenty years earlier. Since the young Dionysius displayed a passion for philosophy, Plato was unwilling to reject this opportunity to influence the politics of the most powerful Greek city of the time. He proved quite ineffective in the intrigues of the Syracusan court, and was barely able to escape safely from his final visit to Dionysius in 360 BCE at the age of sixty-eight. The Seventh Epistle presents a detailed account of the Syracusan adventure from Plato's point of view. It ended in disaster both for Plato and for Sicily. After driving the tyrant out of Syracuse, Dion himself was murdered in 353 BCE. Plato, at seventy-five, responded with an elegy on the death of Dion, ending with the verse "Dion, you who once drove my heart mad with erôs."

Writings

Of the thrirty-six dialogues preserved in the traditional canon (presumably as edited by Thrasyllus in the first century CE), some twenty-six or twenty-seven are generally recognized as the work of Plato. (The authenticity of the Hippias Major is contested; some scholars would also defend the First Alcibiades and perhaps a few others usually regarded as spurious.) The traditional corpus includes thirteen Epistles, most of them now recognized as spurious. Two or three of the Epistles have some claim to be authentic; the most important of these, for both philosophical and biographical reasons, is Epistle VII.

The only reliable guide to the chronology of the dialogues is the division into three stylistic groups, established by Campbell and Ritter in the late nineteenth century.

Group I: Apology, Charmides, Crito, Cratylus, Euthydemus, Euthyphro, Gorgias, [Hippias Major ], Hippias Minor, Ion, Laches, Lysis, Menexenus, Meno, Phaedo, Protagoras, Symposium

Group II: Republic, Phaedrus, Parmenides, Theaetetus

Group III: Sophist-Statesman, Philebus, Timaeus-Critias, Laws

Group III was identified first (as the "late group") on the basis of several independent studies. These six dialogues are marked by very strong stylistic peculiarities typical of the Laws, which we know to have been written towards the end of Plato's life. Group II includes dialogues stylistically akin to the Republic, which show relatively few distinctive features of Plato's late style. Group I is the default class, the remaining sixteen or seventeen dialogues, from the Apology to the Symposium and Phaedo, in which Plato's brilliant conversational style bears none of the distinctive marks of the late period.

This chronological division into three groups is only partially in agreement with a conventional division of Plato's dialogues into early, middle, and late. The dialogues of Group III are all truly "late." (There was a brief attempt to date the Timaeus earlier for philosophical reasons, but that attempt has generally been recognized as a failure. The style of the Timaeus was from the beginning recognized as belonging to the latest period.) But the usual classification of "middle" dialogues ignores chronology altogether. It combines two dialogues of Group II (Republic, Phaedrus ) with two from Group I (Symposium, Phaedo ) solely on grounds of philosophical content. Despite their stylistic differences, all four works present the classical version of Plato's doctrine of Forms. A popular view of Plato's development locates these dialogues in a "middle period," divided on the one hand from the more "Socratic" dialogues of an earlier period, and, on the other hand, from the attack on the theory of Forms in the Parmenides and hence from the more critical philosophy of the Theaetetus and Sophist. This tripartite division is not supported by the Campbell-Ritter chronology of the three groups, since stylistically the Parmenides and Theaetetus are not later than the Republic. The notion of a "Socratic" period depends upon a particular interpretation of the role of Socrates in the earlier dialogues.

Socrates

The figure of Socrates appears in every Platonic dialogue except the Laws, and he is the chief speaker in all but five. This raises two difficult problems for interpreting Plato's work. How far does Socrates speak for Plato? And what is the relation between the Socrates of Plato's dialogues and the historical figure? We deal here with the historical question.

Since Socrates wrote nothing, we are entirely dependent on other writers for knowledge of his thought. The traditional attitude of historians has been to rely on the picture of Socrates presented in Plato's earlier dialogues, supplemented or confirmed by information from Xenophon and Aristotle. The result has been to take dialogues such as the Laches, Euthyphro, and Protagoras as providing a historical account of Socrates, as a moral philosopher who identifies virtue with knowledge, denies the reality of akrasia (weakness of will), and systematically pursues definitions of the moral virtues. In these "Socratic" dialogues Plato is thought to be closely following the thought and methodology of his master. On this view, Plato will only gradually develop his own philosophy, first with the doctrine of recollection in the Meno and then with the theory of Forms in the Symposium and Phaedo. This view can be supported by evidence from Aristotle, whose references to Socrates match the picture given in these "early" dialogues.

This account of Socrates has been treated with skepticism in much recent scholarship, because of a realization (pioneered by Gigon but developed by others) that the Socratic literature is a form of fiction rather than of historical biography. This fictional status is particularly clear in the remains of Socratic dialogues by other authors, such as Aeschines or Phaedo, but also in Xenophon's Symposium and in Platonic dialogues such as the Menexenus. Plato's portrait of Socrates is no doubt generally faithful to the moral character of the man as he saw him. But in regard to details of Socratic philosophy and argumentation, Plato would be at least as free as a modern novelist would be in dealing with historical figures. Furthermore, in the view of skeptical critics, Aristotle cannot serve as a reliable witness. He arrived in Athens as a youth more than thirty years after Socrates' death, and his picture of Socrates can be explained as his own inference from the Platonic dialogues. Judged as a historian of philosophy, Aristotle has serious faults. He generally sees his predecessors through the prism of his own scheme, and his account of the development of Plato's thought is particularly suspect. Aristotle's report of Cratylus's early influence on Plato is scarcely compatible with Plato's own portrait of Cratylus in the dialogue of that name; and Aristotle's claim that Plato's Theory of Forms was derived from the Pythagoreans is not supported by his own account of Pythagorean doctrine. Aristotle never mentions Plato's much more profound debt to Parmenides' concept of Being.

For all these reasons, a critical reader may well doubt that we have any reliable information about the philosophy of Socrates. It is perhaps in Plato's Apology that we can best catch a glimpse of the historical Socrates. The Apology is a special case among Plato's writings, since it is not a fictitious dialogue but a courtroom speech, the representation of a public event at which Plato claims to have been present. From this and other sources we can form a vivid picture of Socrates' powerful personality, his strong moral character, and his remarkable skill in elenchus, that is, in arguing his interlocutors into contradiction. But beyond the firm refusal to act unjustly and the conception of virtue (aretê ) as care of one's self, or care of one's soul, our historical knowledge of Socrates' philosophical views seems to be limited to a handful of moral paradoxes: that no one does wrong voluntarily, that it is better to suffer than to do wrong, that virtue is knowledge, and that no evil can happen to a good man. In order to put philosophical flesh on this skeleton of doctrine, we must turn to the dialogues. But then we can no longer distinguish what derives from Plato's memory of the historical Socrates from what has its source in Plato's own artistic and philosophical imagination.

The First Dialogues: Apology, Crito, Ion, Hippias Minor, Gorgias

Although we do not know the chronological order of the dialogues in Group I, it is natural to begin with the two dialogues directly concerned with Socrates' trial and death, Apology and Crito, and with two other very short dialogues, Ion and Hippias Minor. We connect with this group a much more substantial work, Gorgias, which many scholars would put later. These five dialogues serve to illustrate the wide range of Plato's philosophical concerns, while at the same time revealing no trace of the metaphysics and epistemology that we recognize as distinctly Platonic.

Although it may have been written ten or twelve years after Socrates' death, the Gorgias presents a systematic exposition of Socratic moral doctrine and a strong defense of this view against anti-moralist attack. The Gorgias repeatedly recalls Socrates' trial and matches it with a judgment myth, in which the souls of those who are truly guilty of injustice will be punished. In the Crito, Socrates had formulated as his fundamental moral principle that one should never act unjustly, never return a wrong for a wrong. Socrates is prepared to die for this principle, and is unwilling to save his life by an unjust escape from prison. "It is not living that is of chief importance, but living well, and that is living honorably and justly" (Crito 48b). Crito agrees. Socrates recognizes that, between those who accept and those who reject these principles, "there is no common basis for discussion, no koinê boulê, but they must despise one another's views" (49d). In the Gorgias there is no such agreement, and the principle of justice is itself at stake. The Greek conception of justice (dikaiosunê ) is broad enough to cover morality generally, understood as respect for the rights of others. (Thus Aristotle defines "justice" as virtue in regard to others.) Socrates in the Gorgias has much the same task as later in the Republic : to defend the principle of morality against opponents who endorse the ruthless pursuit of wealth and power. The question, "Why be moral?" is posed here in dramatic form, against the background of Socrates' own fate as a martyr for moral principle.

The Socratic elenchus as practiced in the Gorgias is able to show that the anti-moral positions of Polus and Callicles are basically incoherent, but Socrates is less successful in his positive defense of the principle of morality. He relies here on an analogy between virtue or moral integrity, as an internal order of the soul, and the role of order and harmony in other domains: in the health of the body, in the order of the cosmos, and in the successful products of the arts. But an argument from analogy has its limitations. What is lacking here is a positive psychological theory (like the tripartite theory of the Republic ) as the basis for a constructive argument in support of the conception of virtue as the harmony and health of the soul.

The most important positive doctrine of the Gorgias is the claim that all actions are done "for the sake of the good," that is, for a goal or telos that the agent perceives as good (467c–468b). This remains the fundamental axiom in action theory for both Plato and Aristotle; it reappears in the Republic as the supreme Form of the Good, "which every soul pursues, and for the sake of which it performs all its actions" (Rep. 505d 11). In the argument for this principle in the Gorgias, Plato deliberately blurs the distinction between good-for-the-agent and intrinsically or absolutely good. Polus will acknowledge that what people really want is something good, namely good for them or in their interest, but he denies that this is necessarily the honorable or moral thing to do (to kalon ). Plato's point will be that moral knowledge consists precisely in the recognition that what is good absolutely (i.e., virtue) is also good for you, so that it is in your interest to be virtuous. This is Plato's reading of the Socratic paradox that no one is voluntarily unjust.

The Gorgias thus expounds, both by paradox and by systematic argument, the principles of Socratic moral philosophy as exemplified in the Apology and Crito. By contrast, in the Hippias Minor we find Socrates arguing for a more perverse paradox, namely, for the blatantly false proposition that anyone who commits unjust and dishonorable actions voluntarily is a better person than the one who does such actions unintentionally. The interlocutor is unconvinced, and we can only wonder what point Socrates is supposed to be making. This is probably an indirect way of calling attention to the more authentic Socratic claim that in fact no one does such actions voluntarily. But why not? Why does the analogy fail with arithmetic, for example, where the good mathematician makes mistakes on purpose, whereas the bad mathematician does so unintentionally? If moral virtue is a form of knowledge, why is it not to be understood on the model of the arts and sciences? The implicit Platonic answer seems to point to the role of intentions (the verb boulesthai, "to want," is systematically repeated at 366b–367a), and thus to the universal desire (boulêsis ) for the good recognized in the Gorgias. Whatever the implied answer to this paradox may be, the Hippias Minor demonstrates Plato's early preoccupation with the problem of moral knowledge.

Finally, in the Ion Plato develops a different Socratic theme concerning knowledge: the refutation of knowledge claims on the part of the poets (Apology 22b). Instead of attacking the poets directly, Plato begins with their representative, the rhapsode or performer. Socrates' argument in the Ion is a direct refutation only of the claim to knowledge or art (technê ) on the part of the rhapsode, but the positive theory of poetic inspiration applies to the poet as well. According to this theory, the power of poetry comes from the Muse and is transmitted via the poet to the rhapsode, like the attractive power that is transmitted from the magnet stone via iron rings to other pieces of iron. Hence neither the poet nor the rhapsode needs to understand what is going on. Their divine inspiration is non-cognitive: being possessed by a god, they are out of their mind.

The Ion thus presents Plato's first move in the ancient quarrel between philosophy and poetry, a quarrel that will be dramatically represented in the confrontation between Socrates and the poets in the Symposium and will assume canonical form in the criticism of poetry in the Republic. The Ion is indirectly invoked in the last scene of the Symposium, since it provides us with the argument that the narrator has forgotten. In this final episode Socrates is proving to Agathon and Aristophanes, a tragic and a comic poet, that anyone who knows how to compose tragedy by art (technê ) will know how to compose comedy as well (223d). The needed premise is given by a proposition of the Ion, namely, that anyone who possesses the relevant knowledge (technê ) will be able to deal with poetry as a whole, since it is a single art (532c). With a slight revision, Socrates' argument against Ion will serve as well against Agathon and Aristophanes. In contrast with the Republic, where Plato criticizes poetry first on moral grounds (in Book 3), and then on principles of ontology (in Book 10), in the Ion and Apology Plato's criticism is more Socratic, rejecting the claims of poetry to be recognized as a kind of knowledge. It is thus aimed directly against the traditional conception of poets as sophoi or sages, sources of wisdom. For Plato the quarrel between philosophy and poetry is ultimately a culture war, a competition for the moral leadership of Greek society.

In the course of his attack on poetry in the Ion, Plato introduces the important epistemological principle of a one-to-one mapping between a technê and its object: "necessarily, the same art will know the same subject matter, and if the art is different, it will know a different subject" (538a). This correlation between a form of cognition and a definite content or subject matter appears frequently in other dialogues (for example Gorgias 464b, Charmides 171a). In the Republic this principle is invoked to show that knowledge and opinion must have different ontological objects (V, 478a); in the Timaeus a similar principle is implied as premise in an argument for positing Forms (51d). Problematic in its particular applications, this principle reflects Plato's fundamental realism in epistemology. Truth in cognition reflects reality in the object known: "What is completely is completely knowable; what is not in any respect is unknowable in every respect" (Rep. 477a 3).

Definition and Aporia: Laches, Charmides, Euthyphro, Protagoras

On a traditional view, these four dialogues provide something like a philosophical portrait of the historical Socrates: pursuing the topic of moral virtue, seeking definitions of the virtues (courage in Laches, temperance in Charmides, piety in Euthyphro ), identifying virtue as a kind of knowledge, and denying the reality of akrasia. Most descriptions of the philosophy of Socrates are based upon the evidence of these dialogues, as supported by Aristotle's account. But if Aristotle's account of Socrates is derived from his own reading of these dialogues, his testimony is of no independent historical value. In at least one case Aristotle's report can be seen to be directly dependent on a Platonic dialogue, since for the Socratic denial of akrasia he quotes the Protagoras verbatim (N.E. VII.2, 1145b 24, citing Prot. 352c 1).

On the fictional view of the dialogues proposed above, what we have in the Protagoras and the dialogues of definition is not documentary evidence for the historical Socrates but rather Plato pursuing Socratic themes in his own way, and with his own philosophical goals in view. Thus the Laches and the Euthyphro offer a subtle lesson in the logic of definition, which will be completed in the Meno. And in the Protagoras we find something entirely new and problematic: a hedonistic anticipation of rational choice theory that is unparalleled in other dialogues.

Whatever Socrates' own concern with definition may have been (and there is no trace of this either in the Apology or the Crito, nor in the Ion and Hippias Minor ), the treatment of definition in the Laches-Charmides-Euthyphro-Meno has a systematic quality and an epistemic orientation that is distinctly Platonic. Unlike the more straightforward search for a definition of rhetoric in the Gorgias, which does not raise epistemological issues but leads instead to a formula acceptable to all parties, the attempt to define virtues in these four dialogues of definition is formally aporetic and regularly unsuccessful. Although the search for a definition always fails, in two cases it points incidentally to an account of virtue as the knowledge of good and bad (Laches 198c–199e, Charmides 174b–e). In the Protagoras (as also in Meno and Euthydemus ) virtue is again identified with some kind of knowledge.

The teachability of virtue is a topic debated at length in the Protagoras and Meno, and raised also in the Laches for the special case of courage. The claim of teachability seems to stand or fall with the conception of virtue as knowledge. The Meno makes explicit the principle implied at the end of the Protagoras : Virtue is teachable if and only if virtue is a kind of knowledge (Meno 87b). This assumption reflects the Greek sense that technê and teaching go together. But this principle raises the problem posed in the Hippias Minor : If virtue is a kind of knowledge, how is it different from other, more professional forms of technê ? This question is briefly discussed at the beginning of the Protagoras : The young Hippocrates wants to study with Protagoras not for professional reasons, in order to become a sophist, but for liberal education, the training appropriate for a free man and citizen (312ab). This leaves open the question of what such training should consist in. We must wait for the Republic to get a definite answer to the question of the teachability of virtue. The Protagoras and Meno present arguments for both sides of the question (see below).

The dialogues of definition direct us to the theory of knowledge by two routes: first, by the suggestion that virtue, the target of definition, is itself a kind of knowledge. And second, by the claim that knowledge as such depends on knowledge of essences. Thus in the Laches, where the two generals Laches and Nicias are being consulted as experts on training in virtue, the request for a definition is proposed as a test of their expertise: "if we know what virtue is, we should be able to say what it is " (190c). For if we did not know at all what virtue is, how could we advise anyone how to acquire it? (190b). Similarly, if Charmides is temperate, he should have some notion of what temperance is (Charmides 159a). In the Meno this type of question is justified by the general principle of priority of definition: One cannot know anything whatsoever about X unless one knows what X is (Meno 71b). We will return to this principle below, in discussing the Meno.

It is in the Euthyphro that the notion of essence or whatness, what X is, is most fully articulated as the object to be captured in a definition. To define piety one must specify something quite general, for the pious is "the same as itself in every action… similar to itself and having some one character (idea )" (Euthyphro 5d). The definiens must be not only coextensive with the definiendum but explanatory of it; necessary and sufficient conditions are not enough for a Platonic definition. Socrates wants to find "the very feature (auto to eidos ) by which all pious things are pious." Only then will he be able to "look to this character (idea ) and use it as a model (paradeigma ), so that when any action is of this sort I will say that it is pious, and when it is not of this kind I will say that it is not pious" (6e). The definition offered by Euthyphro ("piety is what is loved by the gods") turns out to fail this test; it is a proprium, an attribute uniquely true of piety, but not an explanatory essence. Socrates complains to Euthyphro: "When you were asked what the pious is, you were not willing to reveal to me its essence (ousia, literally its being or is-ness), but you gave me instead an attribute (pathos ), saying that it belongs to the pious to be loved by all the gods" (11a).

The distinction between an essence and an accidental attribute, so fundamental for Aristotle's philosophy, is here sharply delineated for the first time, but without clear metaphysical implications. In the dialogues of definition, including the Meno, essences are presented as logical or epistemological concepts, as items corresponding to a definition, an item true of all the cases, and hence able to serve as a criterion for the use of a term, but without any definite ontological interpretation. Despite the terminology of eidos and idea, which in later dialogues will serve to designate the Forms of classical Platonic theory, the essences of the Euthyphro and Meno are not articulated as structures in the nature of things, neither as immanent nor as transcendent forms. In this situation the reader is free to assume either that the author of these dialogues has not yet decided on an ontological interpretation for his definienda, or that he has chosen to reserve this task for other dialogues, such as the Symposium and the Phaedo.

Transitional Dialogues? Lysis, Euthydemus, and Meno

These three dialogues present or allude to typical Platonic themes in epistemology and metaphysics, but without any definite formulation of what will be the standard theory of the Phaedo and Republic. Hence they are sometimes described as "transitional." It is again left to the reader to regard these statements either as deliberately incomplete or as reflecting Plato's own indecision.

Lysis and Euthydemus form with Charmides a literary group of dialogues with similar introductory episodes, presenting a charming school scene in which Socrates converses with handsome boys or adolescents. (The setting of the Laches is comparable, but in that dialogue Socrates converses only with the fathers and not with the boys.) The question of education is implicitly raised by the setting in each case, and discussed at length in the Euthydemus and Meno. Aside from the literary setting and the general theme of education, in other respects these three "transitional" dialogues are very different from one another.

The Lysis is concerned with the topic of friendship and love, a topic discussed below in connection with the Symposium and Phaedrus. There are a number of parallels between the Lysis and Symposium ), the most striking of which is the concept of a final object of love for the sake of which everything else is loved. In seeking to explain in the Lysis why anything is dear or desirable (philon ), Socrates suggests that one thing is dear for the sake of another, as a doctor is desirable for the sake of health, but that such a regress cannot go on indefinitely: "we must either give up or come to some starting-point (archê ), which will no longer refer to some other dear, but we will come to "that which is primarily dear" (prôton philon ), for the sake of which we say that all other things are dear … This is what is truly dear; the other dear things are like its images" (Lysis 219c 5–d5). Since the form of the argument resembles Aristotle's thesis (in N.E. I.7) that happiness is the supreme good, for the sake of which everything else is good, some scholars have used this parallel to interpret the Lysis passage as a reference to happiness. But there is nothing in the text to justify this interpretation. On the contrary, the formula "for the sake of which" refers to the good in passages cited above from the Gorgias and Republic (section IV). Furthermore, the context in the Lysis identifies the "dear" (philon ) as the good and the beautiful (216c 6–d2). Above all, the formula "that which is primarily dear" (ekeino ho esti prôton philon ) is a close approximation to the standard terminology for the Forms in other dialogues, and specifically for the Form of Beauty in the Symposium (auto ho esti kalon 211d 1). This anticipation of the technical language for Forms, together with the generally quite abstract form of the arguments about friendship, sets the Lysis apart from more typical "early Socratic" dialogues such as the Laches or the Euthyphro.

The Euthydemus is equally non-standard for other reasons. Plato presents an entertaining satire on two elderly sophists, the brothers Euthydemus and Dionysodorus, who claim to teach virtue by a shortcut method, and who display their art by confounding the student with a rapid series of fallacious arguments. Their art of unscrupulous refutation, or eristic, is designed to provide the sharpest possible contrast with the genuine Socratic elenchus, represented here not by the usual refutation but by a constructive protreptic in which Socrates argues that wisdom is the only good, ignorance the only evil, and hence that in order to enjoy happiness and a good life (eu prattein ) one must pursue wisdom and knowledge.

Both Socrates' protreptic and several of the Sophists' refutations contain enigmatic allusions to Platonic doctrines presented in other dialogues. In the most surprising of these allusive passages, the young Clinias compares mathematicians to hunters because they must turn over their findings to someone else. Just as hunters turn over their catch to cooks, who know how to make good use of it, mathematicians, if they are wise, will turn over their discoveries about reality (ta onta ) to dialecticians (hoi dialektikoi ) to make use of (Euthydemus 209c). This subordination of mathematics to dialect is scarcely intelligible without the epistemology of Books VI and VII of the Republic. But this is not the only case where the Euthydemus anticipates doctrines to be developed in later dialogues, including an allusion to recollection (296d 1) and a hint that the relativism of Protagoras may be self-refuting. (Compare Euthydemus 286c 2–4 with the peritropê argument of Theaetetus 170a–171c.) There is also a rough version of the principle of non-contradiction (293b 8–d 1), and a kind of caricature of the problem of the presence of "the beautiful itself" in the many beautiful things (300e–301a). The Euthydemus is thus one of the most comical and also one of the most puzzling of all the dialogues.

Meno and Recollection

The Meno introduces the doctrine of recollection, which plays an important role in two later dialogues, the Phaedo and Phaedrus. Like the sixteenth-century theory of innate ideas which it inspired, Plato's doctrine of recollection is an antecedent both for the Kantian notion of a priori knowledge and for contemporary theories of innatism in psychology. The fundamental thesis of the Platonic doctrine is that there is something in the nature of the human mind that predisposes it to grasp the nature of reality: "the truth of beings (ta onta ) is forever in our psyche" (Meno 86b 1). The supernatural form this doctrine takes in Plato is determined by its association with the Pythagorean doctrine of transmigration, which implies a previous existence for the human soul. The Phaedrus give a mythical account of prenatal experience, in which human souls travel with the gods outside the heavens, to a vision of ultimate reality described in terms of the Platonic theory of Forms. It is our recollection of this prenatal vision of transcendent Beauty that explains the phenomenon of falling in love.

In the Phaedo as well recollection takes as its object the eternal Forms, illustrated in this dialogue by the Equal itself, as distinct from sensible equals. This choice of the Form of Equality in the Phaedo connects recollection with mathematics, as in the Meno, where recollection is illustrated by the geometry lesson to an uneducated slave boy. (The boy is led by a series of questions to see, first, that he is unable to double a square by numerical additions to the side, and then to recognize the solution when Socrates draws the diagonal.) But it is not only mathematical concepts but conceptual thought generally that is involved in recollection. As the Phaedrus insists, a human soul must be able "to understand what is said according to a form (eidos ), passing from many sense perceptions to a unity gathered together by rational thought. And this is recollection of what our soul once saw when it traveled together with a god and looked beyond what we now call reality and was able to rise up into the really Real" (Phaedrus 249bc). The myth of the Phaedrus thus represents Plato's most brilliant expression of the classical Greek view that reason (nous ), the cognitive capacity to understand the world, constitutes the immortal, godlike element in the human psyche.

The Meno presents a simpler version of the doctrine, without any explicit reference to the theory of Forms. Recollection is introduced in response to Meno's paradox about learning something new, or seeking for something you do not know. Meno in turn is responding to the principle of "Priority of Definition," which claims that you cannot know anything about X unless you know "what X is." How then do we ever get started? Recollection answers that what we learn is not new; we only need to be reminded. In the fuller doctrine formulated in the Phaedo and Phaedrus, it is not Socratic questioning but sense perception that serves to trigger a conceptual understanding (of equality, beauty, and the like) that is provided by the mind from its innate resources.

The "transitional" status of the Meno is indicated not only by the fact that it presents the simplest version of recollection, but also by tentative statements of other themes that are more fully developed in the Phaedo and Republic : the distinction between knowledge and opinion, the method of hypothesis, and two levels of virtue, one dependent on right opinion and the other on knowledge (Meno 99a–100a).

Plato's Theory of ErÔs

Love is a central topic in three Platonic dialogues (Lysis, Symposium, Phaedrus ); it also plays an important role in the moral psychology of the Phaedo and Republic. The fundamental idea is expressed symbolically in Plato's etymological reading of philo-sophia as love of wisdom or passion for knowledge (Phaedo 66e2, 68a). In the psychological theory of the Republic, all three parts of the soul are characterized as distinct forms of love: desire for learning (to philomathes ), desire for honor, desire for pleasure and wealth. Thus for the rational part the object of desire is "to know the truth" (581b). Like the religious mystics, Plato makes use of the language of sexuality to express philosophical passion: the true lover of knowledge will not be relieved of his pangs of erôs "until he grasps the nature of each Form with the appropriate part of the soul, and clinging to and mingling with the truly real, he begets truth and understanding (nous )" (490b). Plato anticipates the Freudian notion of sublimation in his account of the channeling of desire (485d); the notion of unconscious Oedipal desires is recognized in his description of criminal dreams (571c–d). There is also a superficial analogy between Plato's tripartite psychology and the Freudian trio of ego, superego, and id, but the second principle is in fact quite different in each case. Plato's thumos or "spirit" is a principle of anger, pride, and self-assertion, in contrast to the guilt-producing and self-punishing aspects of the Freudian superego. What the two psychological theories have in common is the understanding of psychic conflict in terms of deep divisions within the soul.

Plato's theory of erôs has been criticized for devaluing the love for an individual person in favor of love for an abstract principle like the Forms. Thus in the ladder-of-love passage in the Symposium, the lover who follows Diotima's instructions will leave behind his initial passion for an individual beauty in order to rise to more spiritual beauties and finally to the Beautiful itself. Even in the Phaedrus, where the philosophical lovers assist one another in growing the wings of their souls and escape together from the cycle of rebirth, their real love is for the Form of Beauty. But it is misleading to evaluate the Platonic conception of erôs as if it were a contribution to the modern theory of love. Plato's concern with interpersonal love is better illustrated by his treatment of friendship (philia ), as depicted in the case of the two boys Lysis and Menexenus in the Lysis. So it is the Lysis that provides Aristotle with the starting point for his own theory of friendship. The philosophical importance of erôs for Plato lies not in its role as a relation between persons but rather in its function as the energy driving us to pursue what we take to be good (or good-and-beautiful) and hence, when properly enlightened, to pursue the Good itself. Rightly directed, erôs is philo-sophia, the passion for wisdom. Only wisdom can recognize the true nature of the Good, "which every soul pursues and for the sake of which it performs all its actions" (Rep. VI, 505d11). It is in this sense, as knowledge of the good, that wisdom is equivalent to virtue, since it guarantees that the erôs of the wise will be directed to what is objectively good. The emotional drive in question is, however, intrinsically ambivalent; in the absence of wisdom, erôs can also become the criminal passion that impels the tyrant to psychological destruction in Republic Book IX.

Virtue and Knowledge: Plato's Moral Psychology

Many scholars have followed Aristotle in holding that Socrates identified virtue with wisdom and thus ignored the power of irrational emotion to influence action. The conception of virtue as a form of knowledge is represented in a number of dialogues. The neglect or denial of irrational emotion is most extreme in the Protagoras, where Socrates interprets akrasia as an error in measuring future pleasures and pains. What is generally understood as being overcome by passion is there explained as an intellectual mistake. No other Platonic text explicitly denies the reality of akrasia. But several passages in the Gorgias and Meno have been taken to imply this, by suggesting that everyone desires good things, and hence that virtue consists only in the knowledge of good and bad, that is, in the ability to choose the goal of action correctly.

Nowhere, however, does either Plato or Socrates maintain that all desires are desires for the good. On the contrary, the Gorgias implicitly distinguishes between boulesthai as desire for good things and epithumia as desire for pleasure (so explicitly at Charmides 167e; this distinction between rational desire or boulêsis and non-rational desire or epithumia becomes fixed in Aristotelian terminology). The doctrine that virtue is a kind of knowledge can be understood as a paradoxical exaggeration, designed to focus attention on the practical importance of a correct conception of the good, and hence on the value of the Socratic elenchus in leading interlocutors to recognize their own ignorance. But in the face of this exclusive focus on moral knowledge, the existence of akrasia (that is, of people acting against their better judgment) is a challenge. The last section of the Protagoras was written in response to this challenge. But some readers will doubt that either Plato or Socrates ever held the extreme view presented in this dialogue, namely, that the intellect is all-powerful in the control of human action, so that akrasia is simply an error of judgment and vice is always due to ignorance.

What is clear, in any case, is that if Plato ever held such an intellectualist view, he abandoned it in the Republic. The exposition of the tripartite psychology includes an unmistakable description of akrasia in the story of Leontius (who is disgusted at his own weakness in "being overcome by the desire" to gaze at corpses, Republic 440a 1). In this tripartite theory, two out of three psychic principles represent emotional drives that can conflict with, and sometimes overcome, the rational judgment of the logistikon (the calculating part) as to what is best to do. These two principles are the thumos, or "spirit" of anger and pride, and the epithumêtikon of animal appetite—hunger, thirst, and sexual desire. The division into three parts rests upon a careful distinction between sheer desire, for example thirst as desire to drink, and the rational desire for something good, as desire for a good drink. The aim of Plato's tripartite division is precisely to account for the phenomena of psychic conflict, in this case between the desire of a thirsty man to drink and his rational judgment that the water is not good to drink.

On the basis of this division into three parts of the soul, each with its characteristic desire, Plato provides a psychological definition of the virtues in terms of the harmonious working together of all three parts. It is the function of the rational part (logistikon ) to rule over the others in deciding what is the best thing to do; and wisdom is the excellence of this part in judging well. Courage is the excellence of the spirited part, maintaining its loyalty to the commands of reason and law in the face of danger and temptation. The other virtues consist in cooperation, that is, in willing obedience to the commands of the rational part. Hence virtue can be defined as psychic harmony, and vice defined as psychic disorder or stasis, civil war between the parts of the soul.

By this assimilation of virtue to psychological health, vice to psychological disorder, Plato formulates his first answer to the challenge to morality (formulated by Thrasymachus in Book I, reformulated by Glaucon and Adeimantus in Book II). But the Republic actually represents two different views of psychic disorder. In Book IV the vices are described in terms of disobedience or revolt on the part of the irrational emotions; in this context, there is no distinction to be drawn between vice and akrasia, conceived as unruly behavior by the lower parts. (This is also the picture of vice presented by the behavior of the disobedient horse in the Phaedrus myth.) In Books VII and IX, on the other hand, the irrational desires are presented not as disobedient subjects but as successful rebels, who have driven reason from the throne and taken its place as rulers in the acropolis of the soul (Rep. 553d, 560b–d). The logistikon now appears as their subject, carrying out their commands. Thus we have in Books VII–IX a conception of vice represented not as akrasia, not as a failure of reason to control the emotions, but rather as moral ignorance, that is, a mistaken conception of the good (as in Aristotle's distinction between vice and akrasia ).

This Platonic distinction between two conceptions of vice, only one of which corresponds to akrasia, is developed in different ways in several later dialogues. Thus the Sophist (228a–229a) distinguishes moral ignorance from ponêria, vice as a kind of disease; the former is to be treated by instruction, the latter by punishment. The Timaeus 86b–e proposes a similar distinction between moral ignorance and madness due to excessive pleasures and pains; the latter is caused by a disordered condition of the body. The Socratic paradox will be maintained for both kinds of vice, since the loss of self-control from bodily causes can be seen as involuntary (Tim. 86e 3). The connection of the non-rational desires with the body rather than with the soul proper, hinted at in the Phaedo and in Republic, is most systematically developed in the Timaeus (42a–e), where the non-rational soul is created by the lesser gods in connection with their creation of the body.

Political Construction: From the Republic to the Laws

The tripartite psychology of the Republic has an exact parallel in the tripartite social structure of the envisaged polis. Corresponding to reason, spirit and appetite are the three classes of rulers, soldiers, and producers (the latter class consisting of farmers and craftsmen). Scholars have suggested that the psychic tripartition is an artifact of this parallelism, and that Plato's moral psychology would more properly take the form of a bipartition into reason and emotion, as in Aristotle's Nicomachean Ethics (I.13) and in modern theories of action based on belief and desire. (Plato actually flirts with such a bipartite psychology in Socrates' first speech in the Phaedrus 237d–e). However, Plato remains loyal to the tripartite psychology in non-political settings as well (in Socrates' second speech in the Phaedrus, and in the Timaeus ). There is a theoretical advantage to recognizing more than one type of non-rational emotions, some of which are more amenable than others to rational control.

It is essential to the scheme of the Republic that the city is conceived as a great organism, just as the psyche is conceived as a micro-community. Unity and cohesion are fundamental principles of excellence for the city as much as for the individual. Plato's political aim, the greatest good for the city, is for the citizens to share one another's joys and sorrows with a unanimity like that of the parts of a human body, where the whole person suffers if a single part is in pain (V, 462a–e). But this organic unity can be achieved only on the basis of a functional division of labor between the three social classes. Thus the political definition of justice in terms of each group doing its proper job (in Book IV) is prefigured by the initial division of labor through which the city comes into being (in Book II). The first society arises from the mutual need of individuals for one another: one to grow food, one to build houses, one to make clothes. Hence the fundamental principle of specialization: one person, one work.

Instead of a social contract theory, in which civil society is conceived as an artifact designed to bring people out of the state of nature, Plato claims to find a natural basis for social life in reciprocal need and the advantages of cooperation (II, 369–370). He thus sees human beings as by nature friendly and cooperative, in deliberate contrast to the Hobbesian view of human nature presented by Glaucon in the ring of Gyges story earlier in the same book (II, 358e–362c). Since the division of labor is to the advantage of all in the political as well as in the economic sphere, the city of the Republic will have a natural cohesion that is absent from the historical cities of Greece, which are (as Socrates observes in a moment of Marxian insight) really two cities, the city of the rich and the city of the poor (IV, 422e–423a). This pathological split will be avoided in Plato's city, because there the ruling classes will have no private property, no money, and no nuclear family to generate selfish preferences. The needs of the rulers will be provided for by the farmers and craftsmen, who alone will have private belongings and wealth. Thus the ideal city will radically separate economic power from political power; the rulers, who alone possess the latter, will be systematically excluded from the former.

The political structure of the Republic is built up in successive stages, beginning with cooperation and division of labor, then the division into three classes, followed by three culminating waves of paradox in Book V. The first wave is the principle of equal education and access to political power for gifted women; the second wave is the community of wives and children, in other words, the abolition of the nuclear family. (This innovation brings with it some extraordinary marriage arrangements requiring a great deal of systematic deception on the part of the rulers. The principle of benevolent deception was established earlier, in presenting the myth of metals as a noble lie in Book III, 414b–415c.) The third wave, and the condition of possibility for the entire scheme, is rule by philosopher-kings. Only philosophers are competent to rule the city, because only philosophers have access to the Form of the Good and the Form of Justice, the knowledge of which is strictly necessary if the rulers are to make the city just and good. The system of education designed to produce these rulers will be discussed below.

Did Plato abandon these ideals in his later work? An answer to this question is provided in two documents, the Statesman and the Laws. The Statesman is a puzzling work. It purports to define the statesman, or politikos, and to show how he is different from the philosopher. It then defines politikê, the art of statesmanship as a kind of knowledge or understanding that is competent in giving orders, that is, in ruling. But the dialogue never specifies the content of this expertise. It says only that the possession of such knowledge by the ruler (or rulers) is the one indispensable condition of a genuine constitution; all other constitutions can be no better than imitations of this model. Constitutions are ranked by two criteria; the old classification according to rule by one, few or many is now crossed with the new criterion of lawful or lawless. As lawless one-man rule, tyranny is still the worst form of government, but democracy is now the least bad; the best imitation of the model is a constitutional monarchy (302b–303).

How is the ideal model of the Statesman essentially different from the constitution of the Republic ? More precisely, how is this ruler with authoritative knowledge different from a philosopher-king? If we assume that the Republic is in the background, we can see Plato as returning here to familiar territory but from a very different point of view. The Forms are not mentioned as objects of the statesman's expertise (although the dialogue does refer to incorporeal and non-sensible realities); nothing whatever is said about the content of the statesman's knowledge or the nature of his training. We are told only that he will act with justice, and so as to make the city and the citizens better (293d8–9, 297b 2). So presumably the perfect statesman must know what is justice and what is good. Whether or not he knows them as transcendent Forms is left for the reader to surmise.

The one point of general theory that is carefully discussed in the Statesman is whether or not the true ruler's knowledge should in principle be supreme over and above the law, and the answer of this dialogue is a resounding "yes." The regime of legality is an imitation, a second-best, in the absence of the scientific ruler. But nothing in the human world can be superior to genuine knowledge.

At first sight, the position of the Laws is diametrically opposed, for here Plato provides the first philosophical argument in favor of the principle that a city should be ruled by laws rather than by men, and that human rulers should be servants of the law (Laws IV, 715c–d). Law, indeed, is said to be "the dispensation of reason (nous )" (714a). But on a closer look the two texts are not so far apart, since the omniscient ruler of the Statesman is not to be found among us, and according to that dialogue also the best human constitutions must be law-abiding. In the Laws, despite the shift in favor of the rule of law, Plato still yearns nostalgically for the unfettered authority of the truly wise ruler. He is now convinced that human nature is too weak to bear such unlimited power and still remain uncorrupted (IV, 713c with IX, 875b, the source of Acton's principle that absolute power corrupts absolutely). But if such a man could be found, he would not need to be controlled by laws. "For neither law nor any order is superior to knowledge; and it is not right for reason (nous ) to be subordinate to anything" (IX, 875c). This is precisely the thesis of the Statesman.

But the author of the Laws has given up hope of the messianic politics sketched in the Republic. The detailed constitution of the twelve books of the Laws presents a complex political system tightly controlled by an extremely precise legal code, with many invasions of individual liberty, and a social structure very different both from that of the Republic and also from that of fourth-century Athens. The society of Plato's last city prefigures that of Aristotle's Politics, Book VII. In both constructions one social class possesses all the property and is the only group to bear arms and to have political rights, while the mass of the population—the producer class of the Republic —is disenfranchised and reduced to slavery or limited to foreign residents. In the Laws the city has become a club of the leisured class, whose members can devote all of their time to the practice of political virtue, to the study of the law code. and to ritual celebrations in song and dance.

The city of the Laws is an entirely new project, based upon a different political philosophy in which the rule of law is supreme. The constitution includes several realistic political institutions, representing a compromise with Athenian democracy, which introduce a career of public service into the utopian life style of this privileged class of citizens. But despite all these innovations, one fundamental principle of the Republic has been preserved. Although there is no place for a supreme philosopher-king in this law-bound aristocracy, a kind of counterpart is nevertheless preserved in the institution of the Nocturnal Council, introduced at the end of the work. This Council is a group of high officials meeting daily to study the philosophical foundations of legislation, and to revise the laws if need be. To this extent the author of the Republic remains loyal to himself. The construction of a good constitution will still require the presence of philosophy in a position of the highest influence.

Rhetoric and Dialectic: Gorgias and Phaedrus

Rhetoric, the art of public speaking, was developed by the Sophists into a powerful instrument of political leadership; and Plato's chief rival as an educator was the orator Isocrates. Corresponding to its important role in Greek society, rhetoric is a frequent topic of the dialogues, notably in the Gorgias and the Phaedrus, but implicitly also in the Protagoras. In the latter dialogue Socrates presents his own art of question-and-answer as an alternative to, and ultimately a victor over, the art of long speeches represented by Protagoras.

The contest between Socrates and Protagoras is thus a contest between two forms of logos, two methods for winning an argument. In the Gorgias this contrast of methods reflects the deeper contrast between values. The goal of Socrates' rhetorical opponents is wealth and power, and their speeches aim to persuade the majority. Socrates' goal is virtue and knowledge, and his methodology is designed to get only the agreement of his interlocutor (472b). Socrates' characteristic device is the elenchus: deriving a denial of the interlocutor's thesis from premises that the interlocutor will accept. This is the method that Plato describes retrospectively in the Sophist : if someone claims to have knowledge who is in fact ignorant, "since his opinions are confused, it is easy to examine him and to bring these opinions together in discussion and, setting them side by side, to show that they contradict one another" (230b). In the Gorgias, Socrates refers to this as the art of conversation (dialegesthai ) in contrast to the art of speech-making (rhetorikê ) (448d 10). But Socratic dialectic must also be distinguished from eristic, the pursuit of contradiction for its own sake (illustrated by the notorious behavior of the two sophists in the Euthydemus, above in section VI). Unlike this frivolous form of refutation, the Socratic elenchus is designed to free the interlocutor from the false conceit of knowledge, so that the way is opened for him to begin to learn.

In the Republic Plato will transform dialectic, as the art of question and answer, into a much more ambitious and constructive method. We look first at his treatment of rhetoric, which is quite different in the Gorgias and the Phaedrus. In the Gorgias, rhetoric is represented by Socrates' opponents, and in particular by Gorgias, the most famous orator of the late fifth century, and teacher of Plato's rival Isocrates. Gorgias stands for the political power of unscrupulous persuasion, and thus for power without moral responsibility or even, in the case of his followers Polus and Callicles, for power without moral restraint. In the Gorgias, Socrates argues that the rhetorical practice of public persuasion, without principles of justice and without knowledge, is not an art at all, not a technê but a mere empirical knack. To qualify as a technê rhetoric would need the theoretical clarity and contact with truth that are characteristic of knowledge. As seen in the Gorgias, rhetoric clearly lacks both.

In the Phaedrus, by contrast, Plato is concerned with rhetoric not as an instrument of political power but as the form of prose literature, and his sample is not a political speech but a series of epideictic displays on the topic of love. Socrates surprises his interlocutor by not limiting the rhetorical art to speeches in law courts and in public assemblies but generalizing it to cover "the bewitchment of the soul through discourse" (psychagogia dia logôn, 261a8). Rhetoric is here conceived as the art of speaking and writing well. Plato makes one of his notable contributions to literary criticism in the discussion of what he calls "literary necessity" (logographikê anankê ) linking the parts of a composition to one another. Socrates observes that a discourse (logos ) should have an organic form, like a living creature, "so as to be neither headless nor footless, with middle parts and extremities that are fitting both to one another and to the whole" (262bc). It turns out that to produce discourse with this quality, the author must be able to gather similar things into unity, and also divide them by kinds. The art of these collections and divisions is called "dialectic" (266c), and it seems that a true art of writing or speaking must include or presuppose dialectic. If rhetoric is to be a technê, it will not follow the path of the professional orators (269d). True rhetoric would, for instance, require a philosophic understanding of the psyche and of its natural varieties (271d). Like the Gorgias, the Phaedrus ends by rejecting the claims of ordinary rhetoric to be regarded as a technê. But if Plato's judgment of rhetoric in this dialogue tends to be much more positive than in the Gorgias, that is because the art of logoi is here conceived constructively as the art of writing, including philosophical writing, and hence as an application of dialectic rather than an alternative to it.

While dialectic was introduced in the Gorgias and elsewhere as the Socratic art of conversation (dialegesthai ) conducted in question-and-answer form, in the Republic it becomes the highest method of philosophy, the method by which the intellect ascends to the cognition of transcendent Forms. More specifically, it is the method of passing beyond the assumptions (hypotheses) that function as premises of reasoning in the deductive sciences of mathematics. Dialectic thus presupposes the method of hypothesis developed in the Meno and Phaedo, a method derived from mathematics, according to which a problem can be solved conditionally on the basis of an explicit assumption. By subjecting these assumptions to critical scrutiny, dialectic is somehow able to rise above them and thus reach the anhypotheton, the object of unconditional knowledge, in other words the Forms (VI, 511b). The actual practice of dialectic is not described, but its study follows ten years of training in mathematics. Its connection with the conversational method of question-and-answer is preserved in the requirement that the dialectician must be able to "give an account (logos ) of the being (ousia ) of each thing" (VII, 534), that is, to give a systematic answer to the question "What is it?" Giving such an account will necessarily involve a reference to permanent essences or Forms.

Dialectic is described quite differently in the later dialogues, but it remains the highest form of knowledge, the essential method of philosophy. It continues to proceed by question and answer, and to seek the definition of essences in answers to the question "What is X?" According to the Philebus, dialectic still takes as its object "true being which is forever unchanging," the reality "which neither comes to be nor passes away" (58a2, 61e2)," precisely the kind of Being represented by the Forms in Plato's classical theory. In the Sophist and Statesman, however, as in the Phaedrus, dialectic is described in more formal terms, as the method of gathering pluralities into unities and dividing them into kinds (genê ), where the term eidos, which designates a transcendent entity in the classical theory of Forms, seems to be used in the more strictly logical sense of "species" or sub-kind. Instead of the relation to mathematics and the method of hypothesis, which is fundamental for the conception of dialectic in the Republic, it is the method of Division that is central for dialectic in the later dialogues, from the Phaedrus to the Philebus. This shift in the description of dialectic corresponds to a different, less metaphysical way of referring to the objects of knowledge (see further below).

Esthetics and Education: Plato Against the Poets

Can virtue be taught? That is the question raised dramatically in the school scenes of several early dialogues, and discussed at length in the Protagoras and Meno. The conclusion of the Meno is problematic. Socrates insists that we must first define virtue before we can answer this question. Since we have no definition, we must answer it conditionally. If (and only if) virtue is a kind of knowledge, it is clearly teachable. But such virtue is hard to find. What about virtue based on correct opinion (doxa )? It might give the same results as virtue based on knowledge, but would it be teachable? The Meno ends without any clear statement on the question of teachability.

If there is a Platonic answer to this question, it must be found in the educational scheme of the Republic. There is a different but parallel answer in the scheme of education in the Laws. For Plato (as later for Aristotle), an essential function of the city is to make its citizens good, that is, virtuous. Hence education is a central concern in both dialogues. The Republic describes two stages of education, one for the wider guardian class (in Books II and III) and one for the select group of future rulers (in Book VII). Corresponding to these stages we have two accounts of virtue, one based on right opinion (in Book IV) and one on philosophic knowledge (Books VI–VII). The limitations of the initial account of the virtues in Book IV are visible only retrospectively, after the distinction between knowledge and opinion is drawn in Book V. Only after this introduction of philosophy can we appreciate the ambiguous status of wisdom, and hence of virtue generally, as defined in Book IV.

In order to become virtuous, the entire guardian class must have the basic system of education described in terms of music and gymnastics. Only a smaller group will enjoy the training in philosophy, consisting of ten years of mathematical science followed by dialectic and culminating in the vision of the Form of the Good. The first stage of education will produce "citizen excellence" (politikê aretê ); the higher education, accompanied by years of public service, will yield the unqualified virtue of the philosopher-kings. If we take this as Plato's answer to Meno's question "Is virtue teachable?" the answer is: yes, but not by the available means of education. Only a fundamental change in the conditions of social life would make it possible to produce in a regular way the kind of excellence that occurs sporadically today, by good luck or (as the Meno says) by divine dispensation.

Under the more favorable conditions of Plato's city, the character of the guardians will be shaped by a carefully controlled cultural environment, that will include a radical change in the literary and musical content of their education. Plato here defines his position in the culture war he describes as the ancient quarrel between philosophy and poetry (Rep. X, 607b; see above). All of the arts will play an essential role in the moral education of the young guardians, but it is poetry that is the center of Plato's attention, because of the fundamental influence of Homer and the tragedians on Greek moral thought. Since Plato regards their influence as essentially malignant, he would eliminate from his educational scheme major themes of Greek poetry (Books II–III). Following Xenophanes and others, he attacks as immoral the Homeric depiction of the gods. His basic theological principle is that the gods are good, and are therefore (by the law of transitive causation) cause only of the good, and they must be represented accordingly (III, 379a–380c). Plato thus avoids the thickets of theodicy; there is no problem of justifying the action of the gods, since they are never responsible for evil. The actions of glorified heroes must also be represented in such a way as to provide a moral paradigm for the young guardians.

Finally, when Plato returns in Book X to the restrictions on poetry, he attacks the imitative arts generally on epistemic grounds, as being at third remove from truth. He also blames the emotional impact of epic and tragedy for relaxing the moral discipline of the soul. Hence the poets are to be banned from Plato's city, and readmitted only if their influence can be morally justified (697b–e). This is a famous challenge to future aesthetic theory. Aristotle's Poetics and Sir Philip Sydney's Defence of Poesie count among the more noteworthy responses to Plato's challenge.

At the same time, a properly controlled aesthetic environment is recognized as decisive for the development of virtue in the young. This includes the visual arts, but poetry and music are of particular importance, since rhythm and harmony, more than anything else, penetrate deep into the soul (III, 401d). Because of the close connection between the beautiful and the good, the young should be surrounded by beauty in all its forms, so that later, when moral principles are presented to them in rational teaching (logos ), they will recognize these as familiar and congenial (402a). The positive use of the arts in education is developed further in the Laws, with special attention to dance, since there will be choruses for the citizens at all ages (Books I–II). Literature and lyre-playing will be essential in education, and the Athenian Stranger who speaks for Plato in the Laws holds up the Platonic dialogue, and specifically the text of the Laws, as a model for the literature to be used in schools (Laws VII, 802 ff; 811c-e). In both the Republic and the Laws, the content of literature and music is interpreted in moral terms: "rhythms and the performing arts as a whole (pasê mousikê ) are the imitations of the characters of better and worse human beings" (Laws VII, 798e).

Plato's positive evaluation of poetry, implicit in his use of literature in these proposed schemes of education, receives a theoretical development in the account of poetic inspiration as divine madness in the Phaedrus (245a). In the Ion (as in the Apology ) the notion of divine possession for the poet was employed ironically, in order to emphasize the poet's lack of cognitive competence. In the Phaedrus, on the other hand, the madness of artistic inspiration is presented as a positive force, in parallel with the divine madness of love which carries us back in recollection to a prenatal vision of the Forms. Plato never says that artistic experience, like erotic experience, can trigger recollection of the Forms. But it is easy to see how a later Platonist such as Plotinus (and his followers, such as Proclus), less fearful than Plato of the moral and intellectual dangers from poetry, could make use of the Phaedrus parallel between poetry and love to develop a powerful conception of art as a privileged mode of access to a higher level of metaphysical reality. This was a theory much in vogue among the Romantics of the nineteenth century, who took over Plato's theory of poetry as divine possession, deprived it of its ironic sting, and transformed it into a theory of creative genius.

The Classical Doctrine of Forms

The centerpiece of Platonic philosophy is the metaphysical theory of Forms or Ideas, presented in three dialogues (Symposium, Phaedo, and Republic ), utilized in two others (Cratylus and Phaedrus ) and criticized in a sixth (Parmenides ). Whether some version of this theory reappears in dialogues later than the Parmenides is a question to be discussed below. The term "idea" is a transliteration of idea, one of Plato's terms for the Forms. Since the English word suggests something mental or psychological, "idea" seems misleading as a designation for Platonic Forms, which are clearly intended to be mind-independent realities.

As we have seen above, the dialogues of definition present the object of definition as the being or essence (ousia ) of the subject under discussion and distinguish it from an ordinary property or attribute (pathos ). The essence is not only true of all and only instances of the subject, but it is also explanatory of being the thing in question. The answer to a question "What is X ?" should say what X is, in the sense of explaining what makes something an X. (Meno 72c 8.; Euthyphro 6d 11). Thus being dear to the gods, although true of all and only pious actions, does not say what pious is, because it does not tell us why the gods favor some actions rather than others (Euthyphro 11a). These logical properties of essences prepare for, but do not imply, the metaphysical doctrine of the Phaedo and Republic.

Similarly, the terminology for definienda in the dialogues of definition prefigures the later terminology for the Forms, but in a pre-theoretical way: eidos and idea are ordinary terms for features, structures, or kinds of things. Aristotle says that Socrates was pursuing universal definitions, but that he did not separate the universals as Plato did (Met. 1078b 30). Hence some scholars have interpreted the essences of Meno and Euthyphro as immanent (Aristotelian) rather than transcendent (Platonic) forms. But the texts do not support such a distinction. For example, the idea of piety is described as a model (paradeigma ) for deciding whether a given action is pious (Euthyphro 6e); but the Euthyphro does not tell us whether this model would be located in the mind or in the nature of things. The ontology of the definienda in these dialogues is left strictly indeterminate.

Plato supplies a metaphysical framework for the objects of definition in the Symposium and Phaedo, with a further development in the Republic. These dialogues introduce the conception of eternal, unchanging Being as location for the objects pursued in dialectic. Plato has taken over from Parmenides this notion of Being or What-is (to on ) as an unchanging reality accessible only to thought or rational understanding (nous ), defined by contrast with the changing realm of Becoming that is accessible to the senses. Plato's conception differs from that of Parmenides in two respects: Platonic Being exists in the plural (ta onta or The-things-that-are), corresponding to the plurality of Forms, while for Parmenides, Being is a unique One; and Becoming is allotted a certain measure of reality, whereas its ontological status for Parmenides seems to be that of appearance only.

This metaphysical conception of the Forms, which is assumed throughout the argument of the Phaedo, is most succinctly formulated in the final description of the Beautiful in Diotima's lesson on love, as reported by Socrates in the Symposium (210e–211b). The Form of Beauty (literally "the Beautiful itself") is there distinguished from the many beautiful things by (1) being one (unique) rather than many; (2) being a Being rather than a Becoming, that is, being eternally and unchangeably beautiful, rather than becoming beautiful at one time and not beautiful at another; (3) being only and always beautiful, rather than beautiful in one respect or for one observer, but not beautiful in another respect or for another observer. Hence (4) the being of the Form, which is accessible only to thought or understanding, is distinct from its appearance in becoming, which is accessible to opinion (doxa ) and sense-perception. (5) Anything else that is beautiful is such only because of its dependence on the Beautiful itself. This ontological dependence is described in terms of participating or sharing in the Form, or imitating the Form by being an image of the Form. (6) Reflecting this dependence is the notion of eponymy: everything called an F is named after the F itself. (7) The converse of the eponymy relation is the principle of one over many: For every plurality of things called F, there is the Form F itself.

The relation between Forms and their sensible eponyms is the most obscure feature in Plato's theory. In the Phaedo, Socrates insists on the derivation of sensible beauty from the Form, but expresses uncertainty as to how this derivation is to be understood: "Nothing else makes it [the sensible thing] beautiful except the presence or communion or whatever connection there may be with the Beautiful itself—I am not sure about this, but [I am sure] that it is by the Beautiful that all the many beautiful become beautiful" (100d). The terminology of participation occurs once in the Symposium, repeatedly in the Phaedo, and once again in the Republic. But this notion of participation as a Form-sensible relation is subjected to a withering critique in the Parmenides (131a–e). In the Republic participation is generally replaced by the language of imitation and imaging or copying; and it is this terminology that reappears later in the Timaeus.

Difficulties with the classical theory will be discussed in the next section. We consider here the intended scope and motivation of Plato's theory. It is often presented as a solution to the problem of universals. This, however, is not only anachronistic but inaccurate, since the concept of universals (which are not properly ousiai, not substances in a strict sense) was introduced by Aristotle precisely as an alternative to Plato's conception of Forms. In the Republic the Being of the Forms is introduced on epistemic grounds as the object of knowledge, in contrast to the imperfect reality of the sensible manifold as object of doxa. (The deficient reality of the many beautiful things is reflected in the fact that they are beautiful in some respects, not beautiful in other respects. Hence they are in some respects, but they are not in other respects. The is of predication is thus taken to express a reality claim for the subject.) The underlying assumption, often reasserted in later dialogues, is that an object of knowledge must be eternally invariant; otherwise the cognition of it at one time would become false at another time (so explicitly at Cratylus 440a). But knowledge must be always true; hence an object of knowledge must be eternally unchangeable.

This is the argument underlying the presentation of Forms as invariant objects of knowledge in Republic V. To knowledge strictly understood corresponds Being strictly understood: "what is completely real (to pantelôs on ) is completely knowable" (Rep. 477a 3). Anything less real can be the object only of imperfect cognition and partial truth. Plato hesitates to present this as an argument, however, since it might seem to imply the priority of epistemic considerations. That would be misleading. Epistemology and ontology go hand in hand for Plato, but it is the real that determines what is knowable and not conversely. It is the stability of Being that makes reliable cognition possible.

This Parmenidean insight constitutes the permanent basis for Plato's metaphysical speculation. It is worked out for the first time in the classical theory of Forms, but it persists as well in later dialogues such as the Philebus and Timaeus. It is in the Sophist that we have the most explicit statement that without stability and invariance there can be no knowledge or understanding (nous ) whatsoever (249b–d). What is distinctive of the classical theory is not the invariance of Being but the one-many and eponymy relations between Forms and sensibles, as expressed at Rep. X, 596a: "We are accustomed to posit some one Form concerning each plurality to which we assign the same name." Thus there will be one Form of Beauty corresponding to all beautiful things, one Form of Good corresponding to all specific goods, and so on. But the passage just quoted from Republic X is destined to cause trouble, for many reasons. For example, it suggests that Forms will be as plentiful as common nouns and adjectives. Plato will have to speak more cautiously about cutting nature at the joints (Phaedrus 265e) and thus make clear that not every distinction between words will mark a distinction between Forms or Kinds of things (Statesman 262b–263b). The scope of the classical theory is originally undefined, but it does seem to be committed to Forms for artifacts as well as for natural kinds. Thus there is a Form for shuttle at Cratylus 389b and a Form for bed at Rep. 596b, 597a.

Less obvious than the Parmenidean-epistemic motivation for the doctrine of Forms, but equally important, is the distinctively Platonic conception of philosophy as a form of love or erôs, the conception expressed in Plato's etymological reading of philo-sophia as "the love of wisdom" (see above). This notion of the philosopher as lover with the Forms as the beloved object provides the original context for the introduction of the theory in the Symposium, where the Beautiful itself appears as the ultimate object of philosophic passion. In the Phaedo the philosopher is said to be ready for death because it is only when liberated from the body that he can hope to obtain the object of his desire, namely, full knowledge of the truth (67e–68b). The Form of Good is the ultimate Form, not only because it is the source of being and knowability for the other Forms, but also because it is "what every soul pursues and for the sake of which it performs all of its actions" (Rep. 505d 11). The doctrine of Forms is thus designed, from the beginning, to provide not only an epistemology and an ontology but also a philosophy of life, that is to say, a theoretical basis for ethics and politics. It is in virtue of his or her access to the Forms, and above all to the Form of the Good, that a philosopher-king is uniquely qualified to govern, since only such access enables them to know what is a good life for individuals and for the city.

These powerful practical implications of the theory of Forms reflect its origin in the Socratic conception of philosophy as a form of life and in the Socratic concern with defining the virtues as the mark of a good life. No interpretation of Plato's theory can be adequate unless it takes into account this profoundly practical bent of Plato's conception of philosophy. The unique character of Plato's metaphysics lies in this convergence between the Parmenidean demand for eternally unchanging reality and the Socratic pursuit of what makes a human life worth living. Thus the original focus of the theory is not on the problem of meaning for general words or concepts but specifically on what we may identify as value terms: the noble and beautiful first of all (to kalon ), the good (agathon ) and the just (dikaion ). The first generalization of the theory is to mathematical concepts (the equal, the greater, and the smaller) and then to health and strength and to every term defined in dialectic, that is, to every essence (ousia ) "on which we put the stamp of what-it-itself-is" (Phaedo 65d 12, 75d 1: auto to ho esti, the most technical expression for the Forms). How far this generalization of the theory is meant to extend is a question to be raised and partially answered in later dialogues.

Parmenides and the Challenge to the Classical Theory

In the dialogue Parmenides Plato brings the two Eleatic philosophers, Parmenides and Zeno, to Athens for an imaginary confrontation with Socrates. This is the first of a series of dialogues in which Socrates is no longer the chief speaker, being replaced here by Parmenides. Since Parmenides was almost certainly dead by 450 BCE (the alleged time of the conversation, when Socrates was about twenty), Plato has ignored chronology in order to introduce Parmenides as a masterful critic of the doctrine of Forms. It is no accident that, in the dialogues generally, Parmenides is the only philosopher who is allowed to win an argument with Socrates. Furthermore, in view of the Eleatic inspiration of Plato's own conception of Being, Parmenides can be trusted as a sympathetic critic of the theory. He is the first to recognize that to give up the theory completely would mean to abandon philosophy (135b–c).

The dialogue divides into two parts. Part I present a series of objections to the Forms, objections that are never explicitly answered by Plato either in this dialogue or elsewhere. Part II contains eight rigorous deductions from the hypotheses That the One Is and That the One Is Not. The conclusions come in contradictory pairs. According to Deduction 1, the One has no properties; according to Deduction 2 the One has all properties, including contraries (e.g., it is both at rest and in motion, both greater than itself and smaller than itself). How the deductions of Part II are related to one another and to the objections in Part I are matters of extreme obscurity. Parmenides introduces these arguments simply as an example of how a philosopher should be trained before attempting to formulate a theory of Forms. These deductions are thus presented as a logical "exercise" (gymnasia ) preliminary to philosophy proper. They nevertheless represent the only fully developed examples of formal dialectic in the dialogues.

Interpretation of the eight (or on some counts nine) baffling arguments of Part II has been a subject of controversy since antiquity. Skeptics saw these apparently contradictory deductions as purely destructive, whereas Plotinus identified the first three hypotheses with his three principal hypostases: the One, Nous and Soul (Ennead V.1.8). Modern views have emphasized the overlap with the mingling of Kinds in the Sophist and other topics discussed in the late dialogues, such as whole and part, rest and motion. Several interpreters have found in Part II Plato's answers to the difficulties raised in Part I. Some commentators assume that all the arguments of Part II are intended as valid; others regard some of the deductions as so obviously fallacious that the detection of fallacy must be intended as an essential part of the training.

Part I begins with a brief statement by Socrates of the classical theory of Forms, presented as a response to Zeno's paradoxes about plurality. Zeno is quoted as showing that, if things are many, they must have incompatible properties, for example they must be both similar and dissimilar. Socrates agrees that such contraries will be true of the sensible many but not of the corresponding Form: Similarity itself will never be dissimilar, and the One itself will never be plural. Socrates' brief statement here of the classical theory is peculiar in two respects: the relation between the many and the corresponding Form is consistently described as participation (metechein, metalambanein ), and the Forms are said at one point to be "separate" (chôris ) from their participants (129d 7). In responding, Parmenides will seize upon this last point: "And do you divide as separate certain Forms themselves, on the one hand, and as separate on the other hand the things which participate in them? And is there in your view some Similarity itself separate from the similarity that we have?" (130b 1–5). Socrates agrees, and thus accepts a fatal replication of the Forms as immanent properties.

Both features—the reliance on the concept of participation and the distinction between Magnitude itself and the magnitude in us—accurately reflect the formulation of the doctrine in the Phaedo (e.g. 102d 7). And both will be exploited by Parmenides in his criticism, where the notion of participation is shown to be incoherent, while the separation between Similarity itself and "the similarity that we have" (or the similarity "in us") leads to a two-world ontology in which our world is structured by immanent forms. In that case the transcendent Forms of Plato's theory become irrelevant and unknowable. This is the conclusion of the last difficulty, which Parmenides describes as the greatest (133b–134e).

As a consequence of Parmenides' criticism, two features of the classical theory as formulated here must be abandoned: namely, participation taken literally as the "sharing" of Forms by sensibles, and the existence of "forms that we have" or "forms in us" separate from the Forms themselves. Among Parmenides' other objections the best known is the so-called Third Man argument, according to which the one-over-many principle of Republic X (that for every group of F s we posit a Form, the F -itself) leads to an infinite regress. The nerve of this argument is the implicit premise that the F -itself is F ; hence if we add the F -itself to the first group of F s, we get a larger group of F s calling for another F -itself; and so on indefinitely. Some scholars have claimed that this premise (the so-called self-predication principle, that F -itself is F ) reflects a logical confusion on Plato's part between being a property and having a property. However, the Sophist makes clear that Plato remained committed to this principle, and recent interpretations have shown that no fallacy need be entailed. At the same time, the second implicit premiss required for the regress, the so-called Non-identity principle (that for any larger group of F s, a new and different F -itself is needed), has no deep Platonic motivation, and its role in generating the regress can be blocked in several different ways. More problematic than the Third Man argument is the parallel objection against the conception of Forms as models (paradeigmata ), where the dependent relation of participation is understood in terms of similarity or being a likeness of the Form (132d–133a). This objection seems to attack the central concept of imaging or imitation, which replaces participation in the doctrine as reformulated in the Republic and Timaeus. How much of the classical theory of Forms can be thought to survive the critique of the Parmenides will depend in part on the interpretation of this model-copy relation as developed in the Timaeus.

Theaetetus and Sophist : Survival of the Forms? the Later Dialectic

The Theaetetus and Sophist stand in the shadow of the Parmenides : both dialogues refer to the conversation between Socrates and Parmenides as if it were a historical event (Theaet. 183e 7; Soph. 217c 5). As a consequence, both dialogues distance themselves from the classical theory of Forms. Neither dialogue denies the existence of Forms, and both refer to concepts or entities that recall Forms. But neither dialogue asserts the metaphysical dualism of the classical theory. The Sophist even subjects this theory to a new round of criticism. It is as if Plato in the Parmenides had wiped the slate clean, and was prepared to make a fresh start in the later dialogues in addressing the basic issues of epistemology and metaphysics.

The Theaetetus is almost the last dialogue in which Socrates appears as the chief speaker (only the Philebus is later), and the last one in which his elenchtic function is dramatically displayed. In fact the negative character of the elenchus is uniquely underscored here in the comparison of Socrates to a midwife. The official role of Socrates in this dialogue is not to produce theories on his own (as he did in the Phaedo, Republic and Phaedrus, and will again in the Philebus ) but solely to extract definitions of knowledge from Theaetetus.

Theaetetus's attempts to define knowledge fall into two categories, dividing the dialogue into two unequal parts. The first and longer section corresponds to the initial definition of knowledge as sense perception (aisthêsis ). This definition is ultimately rejected on the grounds that truth, and therefore knowledge, is not accessible to sense perception as such but only to the rational psychic activity that Theaetetus calls doxazein, "having an opinion" (187a). The remainder of the dialogue is then devoted to various accounts of knowledge and error based on this notion of doxa, that is, opinion, belief, or judgment. The results of this second section are equally negative, so that the Theaetetus has the external form of an aporetic dialogue like the Laches or Meno —an unsuccessful attempt to define knowledge. The philosophical content of the Theaetetus is, however, extremely productive in arguments and insights for epistemology and philosophy of mind. Why then is the outcome so negative?

If we relate this discussion to Plato's theory of knowledge as formulated in the Republic, we can see why the enterprise of the Theaetetus was doomed to fail. According to the view of Republic V–VI (reasserted in the Timaeus ), sense perception and opinion (doxa ) take as their object the realm of sensory Becoming, whereas knowledge proper takes as its object only invariant Being. Thus in the Divided Line of Republic VI, both sense perception and doxa belong to the lower sections of the line, devoted to the visible realm, but knowledge belongs at the top with the Forms as its object. In the Republic and Timaeus this view of knowledge as metaphysically grounded is presented as a basic assumption, without detailed supporting argument. In the Theaetetus, in contrast, all attempts to define knowledge avoid any recourse to Parmenidean ontology or to the classical doctrine of Forms. This systematic departure from Plato's classical epistemology can be seen as an application of the method proposed and exemplified by Parmenides in the dialogue named after him: See what follows not only from your own assumption but also from its denial (136a 1). Accordingly, in the Theaetetus we pursue an acount of knowledge from the opposing, non-Platonic point of view. Let us assume that knowledge can be defined either on the basis of sense perception, or on the basis of doxa, and see what follows from either assumption. The Theaetetus thus has the form of a double reductio. Since neither alternative gives a satisfactory result, we are justified in returning to our original point of view. There is still no explicit argument for the Parmenidean postulate (that knowledge in the full sense takes as its object Being in the full sense). But this assumption is supported indirectly, by the failure of the alternative attempt in the Theaetetus to give an account of knowledge that avoids this postulate.

Although the general form of the Theaetetus is thus negative, the positive content is extremely rich. The first section develops a subtle theory of subjective perceptual qualities within the framework of Protagorean relativism, on the basis of a neo-Heraclitean doctrine of flux. Commentators disagree on whether this theory of perception should be read as merely hypothetical or whether it in fact represents Plato's own view of the subject. A decision must depend upon whether or not the Theaetetus account of perception is compatible both with Plato's own version of cosmic flux in the Timaeus and also with his mechanistic account of sense qualities in that dialogue. Of great interest also is the argument known as the peritropê, or "overturning," according to which Protagorean relativism is shown to be self-refuting; since it could be true at most for those who believe it, but false for everyone else, therefore even those who believe it must admit its falsity for the others, that is, for most people (Theaet. 170a–171c).

The final rejection of sense perception as a candidate for knowledge relies upon a new distinction between sense-perception proper, that is, information derived through the sense organs of the body, and "common thoughts" (koina ) like "same" and "different," "one" and "many," that apply to more than one sense modality. The argument concludes that the being of predication and existence, and hence of truth, is not available to sense perception as such. "But if one fails to grasp the truth of something, one cannot have knowledge of that thing" (186c 9). Hence sense perception cannot be knowledge.

The "common thoughts" or concepts (koina ) introduced by this argument include "beautiful" and "ugly," "good" and "bad," as well as "same" and "different," "similar" and "dissimilar" (185a–186a). As non-sensible notions, these koina are clearly suggestive of Forms, but nothing whatsoever is said about their ontological status. There is a closer hint of the classical theory in the famous moral digression of the Theaetetus (where virtue is defined as homoiôsis theôi, "becoming like god" 176b 1): There resemblance at the human level is said to connect us with transcendent models (paradeigmata ) of justice and injustice "established in reality" (en tôi onti hestôta 176e 3). These two paradigms represent two lives, one of which, as a model of injustice, is "godless and most wretched." The context of the digression clearly invokes both the judgment myths of Phaedo and Republic and the moral spirit of the Gorgias ; but there is no unambiguous reference here to Forms as defined in the classical theory.

In the Sophist, Plato returns to questions of ontology with a vengeance. The central theme of the dialogue is the problem of Not-Being, and it is argued that the concept of Being is equally problematic, so that the two concepts must be clarified together. Accordingly, the dialogue surveys a series of metaphysical positions, including both Parmenidean monism and a materialist view that reduces Being to bodily existence. A clearly recognizable version of Plato's classical theory is discussed as the doctrine of "the friends of the Forms." As in the Parmenides, a sympathetic critique is guaranteed here by the presence of a metaphysically oriented philosopher as protagonist. As a pupil of Parmenides, this "visitor from Elea" can subject both Parmenides' account of Being and Plato's own theory to constructive criticism. In particular, the Stranger's critique of the Friends of Forms shows that the classical theory must expand its ontology to make room for motion and change as a kind of Being. How this is to be done is left for discussion elsewhere, presumably in the Timaeus. The Timaeus also pursues the most puzzling suggestion of the Stranger's critique, namely that there must be a place among the Forms for Intelligence (nous ) and hence for life and soul (Sophist 248e–249d).

The doctrine of Forms reappears in the constructive argument of the Sophist as a theory of Kinds (genê ) that are capable of combination or participation with one another; dialectic is accordingly redefined as the science of "dividing according to Kinds," knowing "which Kinds harmonize with which, and which do not admit one another" (253b–d). Although in this dialogue we set out to define the Sophist, we seem to have found the philosopher instead, since this dialectical art belongs only "to one who purely and rightly philosophizes" (253e). The description of the philosopher appeals here to the visual imagery of the classical theory: The philosopher is said to be so hard to see because of the brightness of the region "where he is attached always in reasoning to the form (idea ) of Being; for the eyes of the soul of most people cannot bear for long the sight of what is divine" (254a). The metaphysical discussion is, however, left incomplete. The Eleatic Stranger speaks of participation only between Forms or Kinds; nothing is said of the relation between Forms and their sensible eponyms.

Instead of metaphysics the new theory of participation between Kinds offers something like transcendental logic. "It is through the weaving-together of Forms (eidê ) with one another that rational discourse (logos ) has been given to us" (259e). The most elementary weaving-together (symplokê ) is between noun and verb to form the basic logos of a sentence or statement (262c 6). Plato thus introduces the subject-predicate analysis of sentence structure that served as the basis for Aristotle's own theory of predication. Exactly how this analysis is applied in the detailed account of Not-Being is a matter of dispute, but it is clear that the Form of Not-Being is explained by reference to two other Forms, Being and Otherness. (In effect, negation is analyzed in terms of non-identity.) The Sophist thus opens up an entirely new dimension in the theory of Forms: a network of logical and semantic relations between concepts or Kinds, such as whole-part or logical inclusion, combination or extensional overlap, and mutual exclusion.

This conception of dialectic as "dividing according to Kinds" is reflected in the method of Collection and Division that was described in the Phaedrus (265d–266c) and is systematically applied here in both dialogues, in successive definitions of the Sophist and the Statesman. As was noted above, in these definitions the terms genos (kind) and eidos (form) seem to be used in their logical sense simply as "genus" and "species," and the ontology of the Forms is apparently left indeterminate. At the same time, the Eleatic Stranger speaks more definitely of "incorporeal beings, the greatest and finest," which have no images adapted to sense perception but can be clearly indicated only by rational discourse (logos ); it is for the sake of these beings that the dialectical definitions are pursued (Statesman 285e–286a). In such a passage, as in the reference to the divine idea of Being at Sophist 254a, there is a clear reminder of the classical theory. But nothing is said in either the Sophist or Statesman to indicate how the dualism of the Phaedo and Republic is to be altered or preserved.

Philebus and the Return of Socrates

In the Philebus the problems of ontological dualism and participation are directly confronted for the first time since the Parmenides. These issues are presented here within the broader context of relations between the One and the Many. As in the Parmenides, the problem of participation is distinguished from superficial or eristic ways of being at the same time one and many (as one subject with many properties, or one whole with many parts). The serious problem arises only when we distinguish unities that do not belong to "what comes to be and perishes" but are truly beings and truly unities, like the one Beautiful and the one Good. (Among the examples of ungenerated and imperishable unities listed at Philebus 15a are One Human Being and One Ox, thus providing a partial answer to the Population Problem of Parmenides 130c 1. Another partial answer is given in the discussion of Forms of Fire and other elements at Timaeus 51b–52a.) The question then is how such unities, "admitting neither generation nor corruption, can remain one and the same while coming to be in many and infinite cases of becoming, either one unity being scattered and becoming many, or (most impossible of all) being separate from itself as a whole" (15a–b, recalling the critique of participation at Parmenides 131a–c).

A full discussion of these metaphysical issues is avoided in the Philebus, however, because of pressure from the prior question whether pleasure or knowledge is the good and the cause of a good human life. The relation of eternal Forms or Monads to sensible becoming is reformulated here in the light of "an immortal and unaging attribute (pathos ) of discourse (logoi )," an attribute rather cryptically identified as the claim that "the identity of one and many generated by discourse (logoi ) circulates in every way among everything that is ever said" (15d). As the best way out of this confusion, the dialectical method of collecting unities and distinguishing pluralities is presented as a gift from the gods and the basis for all art or science (technê, 16c 2). The discussion thus shifts from the problems of ontological dualism to the dialectical project of discerning unity and plurality in the various kinds of pleasure and knowledge. Instead of metaphysics we are given the method of Division, based on the principle (tossed down from heaven by some Prometheus) that "things that are said to be in every case (or "things said to be forever," ta aei legomena einai ) are derived from one and many, and hence have Limit and Unlimited in their nature" (16c).

These principles of Limit and the Unlimited, introduced here by Plato for the first time, are apparently borrowed from the Pythagorean philosopher Philolaus, who claimed that "Nature in the world-order has been fitted together from unlimited [constituents] and from limiting ones, both the world-order as a whole and everything within it" (fragment 1). In the Philebus these two principles provide the basis for a fourfold cosmic scheme that includes several ideas figuring also in the cosmology of the Timaeus. "All the beings that are now present in the universe" are analyzed as a blended Mixture of Limit and Unlimited, under the causal influence of Intelligence (nous ). In this scheme, as in the Timaeus, causality is interpreted as the purposeful act of a maker, or dêmiourgos. Also common to the Timaeus is the introduction of a world soul (Philebus 30a–d). But the Philebus principles of Limit and Unlimited do not correspond exactly to anything in the Timaeus ; they figure here as immanent components of Becoming, entering as ingredients into a Mixture that represents both cosmic order and a good human life (23b–27c).

This fourfold scheme of Unlimited, Limit, Mixture, and rational Cause is said to be required in order to decide the contest between pleasure and knowledge for recognition as the good. It has already been settled that neither candidate deserves first place; pleasure and knowledge are each shown to be less choiceworthy alone than the Mixed Life that contains both (20d–22c). The issue for the rest of the dialogue is to assign second place in the competition for the good or, more precisely, to determine the relative position of knowledge and pleasure in accounting for the goodness of the good life. It will turn out that, in the ranking of ingredients in the final Mixture, forms of knowledge occupy third and fourth place, while a selected group of pleasures comes in only fifth. The first two constituents of the good life are principles first of measure (metron, metrion ) and next of beauty and proportion (kalon, symmetron ). The fourfold scheme permits Socrates to identify pleasure as a part or species of the Unlimited, while knowledge and intelligence (nous ) belong to the genus of the Cause of successful mixtures.

The central section of the Philebus is a classification of different kinds of pleasure and knowledge. Socrates proceeds to give a subtle analysis of a number of kinds of pleasure, both mental and physical, in order to distinguish pleasures that are true and pure from various mixed and false pleasures. Only pure pleasures of sense and intellect will be admitted into the final construction of the good life. Although all forms of knowledge will be admitted, a ranking is nevertheless carried out between different forms of expertise, in a new version of the Knowledge Line of Republic V. The lowest division is between various manual crafts, including music; for such arts the level of cognition depends upon the extent and precision of the mathematical component. Mathematics in turn is divided into two, with philosophical mathematics representing a higher standard of precision. (Pure mathematics here recalls, but does not exactly correspond to, the higher form of measurement based upon "due measure" in the Statesman. The concept of due measure, to metrion, does, however, return to define the first constituent of the Good Life in the final ranking of the Philebus.)

Finally, the highest form of knowledge is identified as dialectic, which ranks above natural philosophy and cosmology on ontological grounds familiar from the classical theory. For only dialectic is concerned with what is "really real," with Being that is eternal and unchanging; whereas the science of the natural world is a study of what has comes to be and perishes (Philebus 59a, 61e; this is the same ontological contrast that will serve as foundation for the cosmology of the Timaeus 28a–b). Dialectic is here described in terms of classical dualism, including the epistemic contrast with doxai (at 59a 1). But the reader is inevitably reminded of the quite different account of dialectic given earlier in the Philebus, where there is reference not to Being and Becoming but rather to the recognition of unities and pluralities (16b–17a). The old and the new conceptions of dialectic are thus both presented but left uncombined. A similar ambivalence can be seen in the Philebus regarding the problems of metaphysical dualism, which are recognized but not resolved. And in another respect we are left with expectations unfulfilled. Much of the dialogue raises the question of the Good as such and the good-making properties of any mixture, but we reach at the end only "the threshold of the good," in a list of the essential ingredients of a good human life. Any hopes for an account of the Form of the Good are left unsatisfied. It is no wonder that the dialogue ends (67b 11) with the interlocutor reminding Socrates that something has been left out!

We may wonder why Plato brings Socrates back as protagonist in the Philebus, after replacing him with an Eleatic Visitor in the Sophist-Statesman, and again replacing him with Timaeus and an Athenian Stranger in the other late dialogues. No doubt the role of pleasure in the good life was familiar Socratic terrain. But the presence of Socrates might equally serve as a reminder of the dualism expounded by the same figure in the Phaedo and Republic, and also of the unresolved problems raised against Socrates' presentation of this doctrine in the Parmenides. Although the Philebus is not formally aporetic like the Theaetetus, it certainly concludes on a note of incompleteness. If there is a Platonic response to the metaphysical problem recalled here, one must look for it elsewhere, perhaps in the Timaeus.

Timaeus and the Platonic Cosmos

The Timaeus was for many centuries the most influential of all of Plato's works. After the rise of Christianity, it could be regarded as a philosophical exegesis of the creation story in the Book of Genesis. But the profound influence of the Timaeus derives from its mathematical conception of nature, which has also attracted modern admirers from Kepler and Galileo to Whitehead and Heisenberg. For students of Plato the Timaeus has the special interest of offering Plato's only radical reformulation of the classical theory of Forms. The introduction of a spatial Receptacle, on the one hand, and an intelligent Maker of cosmic order, on the other hand, permits Plato for the first time to give a systematic account of the natural world, while deploying new resources to counter the challenges to the classical theory that were formulated in the Parmenides.

In addition to the Receptacle and the Demiurge, Plato's new theory makes use of two other notions developed in the late dialogues: (1) The idea presented in the Sophist that the realm of Being must be enlarged to include motion and change is reflected in the theory of mixture in the Philebus, where the analysis of phenomenal unities gives rise to the new, paradoxical expressions genesis eis ousian, "becoming into being" (26d 8) and gegenêmenê ousia, "being that has come to be" (27b 8). Although the Timaeus reverts to the classical antithesis between Being and Becoming, the cosmological theory deals in fact almost exclusively with Becoming. (2) Without using the terms "Limit" and "Unlimited" from the Philebus, the Timaeus presents a comparable analysis of Becoming as the mixed result of an interaction between two principles, represented here allegorically as Reason and Necessity. The victory of the former over the latter is spelled out in the creation narrative as the shaping of the chaotic motions of the Receptacle by the purposeful action of the Demiurge, "structuring [the pre-cosmic elements] with figures (eidê ) and numbers" (53b 4).

The Timaeus thus interprets the cosmic act of the divine Maker in terms of the normative notion of mathematical measure (to metrion, to symmetron ) expounded in the Statesman and Philebus. Whereas in the epistemology of the Republic mathematics points only upward, to raise the mind towards the Forms, in the cosmology of the Timaeus (and, by anticipation, in the Statesman and Philebus as well) the function of mathematics is also directed downward, to impose order on the mixed products of Becoming, on the good human life as on the order of nature.

By the formal device of Timaeus's monologue, Plato has inserted into this dialogue a prose treatise peri physeôs in the Pre-Socratic tradition, applying a revised theory of Forms to produce his own account of the nature of things, that is to say, of the world of perceptible order and natural change. One goal of this account must be to avoid the "greatest aporia" of the Parmenides by giving an account of the visible cosmos, including human beings, that does not "separate" the phenomenal world from the Forms. Hence, instead of a sensible realm of immanent forms, Timaeus posits as an entity independent from the Forms only the Receptacle, the place where the Forms are imaged. As joint offspring of Forms and Receptacle, the sensible images are like the Mixtures of the Philebus, with no existence independent of their two principles. On the one hand, as modifications of the Receptacle their existence is adjectival rather than substantival. On the other hand, they are no more independent or separable from the Forms than the images in a mirror are independent from the objects mirrored. The Timaeus is insistent on this fact of double dependence. "Since in the case of an image even that on which it depends does not belong to it, but it is always carried about as an appearance (phantasma ) of something else [namely, the Form], it is fitting that it come to be in something else [namely, the Receptacle], on pain of being nothing at all" (52c 2–5). This is Plato's strategy for avoiding the fatal separation between Forms and immanent features of the sensible world, conceived as the "forms that we have" or "forms in us." Properly conceived, images exist only as fleeting determinations of the Receptacle under the influence of one or more Forms.

Of course many questions are left open, including the problem of how Plato can avoid the reciprocity of Similarity which in the Parmenides (in a version of the Third Man argument at 132d–133a) threatens to undermine the explanatory role of images and likeness. Images are said to be impressed on the Receptacle " in an amazing way, hard to describe" (50c 6). The promise to return to this topic is not fulfilled, unless we take the theory of elementary triangles, introduced at 53b, to be the promised account of how images of the Forms are produced in the Receptacle. It is in any case the geometry of these invisibly small triangles that replaces the atomism of Democritus with a more strictly mathematical theory. And it is the same geometric account that provides the mechanism by which the mathematics of Limit and "due measure" imposes order and goodness on the realm of sensory flux. It would seem that the theory of elementary triangles in the Timaeus is the physical expression of the notion of normative mathematics developed in the Statesman and Philebus.

A famous problem, debated already in Plato's school, is whether the creation story is to be taken literally, as positing a chaotic condition of the Receptacle before the Demiurge goes to work, or whether the myth of creation is to be interpreted as an expository device to distinguish different explanatory factors. A non-literal reading of creation would avoid the apparent incompatibility between the Timaeus account of pre-cosmic motions before the creation of the world-soul and the account given in the Phaedrus and the Laws, where the soul as self-mover is the source of all motion and change. A non-literal reading would also dispense with some vexing problems about the ontological status of the Demiurge and his relation to the Forms. (He is described as noêtos, "intelligible" like the Forms at 37a 1.) If we do not have to take creation literally, the Maker simply represents the principle of reason as a causal agency among the Forms.

Some problems will nevertheless remain. Why is the eternal and unchanging model for creation presented as a panteles zôon, a "complete living thing," containing within itself as parts or species all the intelligible living beings (30c–31b)? On the one hand, this eternal model is described in terms that clearly identify it with the Forms of the classical theory. (Thus at 39e 8 the model is referred to as to ho estin zôon, "the what-living-thing-is." This technical expression for the Forms occurs in no other dialogue later than the Parmenides.) On the other hand, nothing in the classical theory prepares us for this conception of the Forms as alive. It is as if Plato in the Timaeus chose to respond to the criticism of the Eleatic Stranger in the Sophist, who complained that the Friends of Forms conceive the highest Being as neither living nor thinking, "but standing immobile like a pious statue, without intelligence" (249a 1). Since it is a fixed doctrine that intelligence (nous ) requires a mind or psychê, and psychê entails life (Sophist 249a, Philebus 30c 9, Timaeus 30b), by bringing the Forms to life the Timaeus evades this criticism. But the reader is left without a clue as to how the life and thought of the Forms are to be understood. Does the divine Intelligence of the Forms possess a divine Psyche of its own, before the creation of the World-Soul? And how is this Intelligence among the Forms related to the divine Psyche established as first source of motion by the argument of Laws X? These are some of the many questions that the myth of the Demiurge allows Timaeus to avoid.

See also Aristotle; Platonism and the Platonic Tradition; Socrates.

Bibliography

works by plato

Editions and Translations

The standard edition of the Greek text is by John Burnet, Platonis Opera. 5 vols. Oxford: Clarendon Press, 1899–1907. Volume I has appeared in a second edition, edited by E.A. Duke, W. F. Hicken, D. B. Robinson, and J. C. G Strachen, 1995, and a new edition of the Republic has appeared as Platonis Respublica, edited by S.R. Slings, New York: Oxford University Press, 2003. There are also editions of the Greek text with French translations in the "Les Belles Lettres" series (13 vols. in 25 parts, Paris: Les Belles Lettres, 1920–1956), and with English translations in the Loeb series (12 vols., London and New York: Harvard University Press, 1921–1935). The best English translations are collected in J. M. Cooper, ed., Plato: Complete Works (Indianapolis, IN: Hackett, 1997).

Modern Editions and Translations of Individual Dialogues

Adam, James. The Republic of Plato. 2 vols. Cambridge, U.K.: Cambridge University Press, 1902.

Burnyeat, Myles. The Theaetetus of Plato. Translated by M. J. Levett. Indianapolis, IN: Hackett, 1990.

Cornford, F. M. Plato and Parmenides. Translation of the Parmenides with commentary. London: Routledge & Kegan Paul, 1939.

Cornford, F. M. Plato's Cosmology. Translation of the Timaeus with Commentary (1937). Indianapolis, IN: Hackett, 1997.

Cornford, F. M. Plato's Theory of Knowledge. Translation of the Theaetetus and Sophist with commentary. London: Routledge & Kegan Paul, 1935.

Morrow, G. R. Plato's Epistles. Indianapolis, IN: Bobbs-Merill, 1962.

Plato. Gorgias. Translation and commentary by E. R. Dodds. Oxford: Clarendon Press, 1959.

Plato. Meno, edited with translation and commentary by R. W. Sharples. Warminster, U.K.: Aris & Phillips, 1985.

Plato. Parmenides. Translated by M. L. Gill and P. Ryan with an introduction by M. L. Gill.Indianapolis, IN: Hackett, 1993.

Plato. Phaedo. Translated with commentary by D. Gallop. Oxford: Clarendon Press, 1975.

Plato. Phaedo, edited by C. J. Rowe. Cambridge, U.K.: Cambridge University Press, 1993.

Plato. Phaedrus, edited with translation and commentary by C. J. Rowe. Warminster, U.K.: Aris & Phillips, 1986.

Plato. Philebus. Translated with Introduction by D. Frede. Indianapolis, IN: Hackett, 1993.

Plato. Statesman, edited with translation and commentary by C. J. Rowe. Warminster, U.K.: Aris & Phillips, 1995.

Plato. Symposium, edited by K. J. Dover. Cambridge, U.K.: Cambridge University Press, 1980.

Plato. Symposium, edited with translation and commentary by C. J. Rowe. Warminster, U.K.: Aris & Phillips, 1998.

Plato. Timaeus. Translated with introduction by D. J. Zeyl. Indianapolis, IN: Hackett, 2000.

works about plato

General Accounts

Crombie, I. M. An Examination of Plato's Doctrines. 2 vols. London: Routledge & Kegan Paul, 1962–1963.

Friedländer, P. Plato. Translated by H. Meyerhoff. 3 vols. London: Routledge & Kegan Paul, 1958–1969.

Grote, G. Plato and the Other Companions of Socrates. 2nd ed., 3 vols. London: Murray, 1867.

Grube, G. M. A. Plato's Thought (1935). Indianapolis, IN: Hackett, 1980.

Guthrie, W. K. C. A History of Greek Philosophy. Vols. 3–5. Cambridge, U.K.: Cambrdige University Press, 1969–1978.

Kraut, R., ed. Cambridge Companion to Plato. Cambridge, U.K.: Cambridge University Press, 1992.

Robin, Léon. Platon Paris: F. Alcan, 1935.

Shorey, Paul. What Plato Said. Chicago: University of Chicago Press, 1933.

Taylor, A. E. Plato: The Man and His Work. London: Methuen, 1926.

Willamowitz-Moellendorff, Ulrich von. Platon. 2 vols. (1919). 3rd ed., vol. I. Berlin: Weidmann, 1948.

Zeller, Eduard. Die Philosophie der Griechen. 6th ed. Hildesheim, 1963.

Particular Aspects of Plato's Work

Allen, R. E., ed. Studies in Plato's Metaphysics. London: Routledge & Kegan Paul, 1965.

Bambrough, Renford, ed. New Essays on Plato and Aristotle. London: Routledge & Kegan Paul, 1965.

Bobonich, C. Plato's Utopia Recast: His Later Ethics and Politics. Oxford: Oxford University Press, 2002.

Burnyeat, M. "Plato on Why Mathematics is Good for the Soul." Proceedings of the British Academy 103 (2000): 1–81.

Cherniss, H. F. Aristotle's Criticism of Plato and the Academy. Baltimore, MD: Johns Hopkins Press, 1944.

Cherniss, H. F. The Riddle of the Early Academy. Berkeley: University of California Press, 1945.

Frede, M. "Prädikation und Existenzaussage." Hypomnemata 18. Göttingen: Vandenhoeck and Ruprecht, 1967.

Gosling, J. C. B., and C. C. W. Taylor. The Greeks on Pleasure. Oxford: Oxford University Press, 1982.

Irwin, T. Plato's Moral Theory (1977). Revised as Plato's Ethics. Oxford: Oxford University Press, 1995.

Kahn, C. H. Plato and the Socratic Dialogue: The Philosophical Use of a Literary Form. Cambridge, U.K.: Cambrdige University Press, 1996.

Klosko, G. The Development of Plato's Political Theory. New York: Methuen, 1986.

Meinwald, C. C. Plato's Parmenides. Oxford: Oxford University Press, 1991.

Morrow, G. R. Plato's Cretan City: A Historical Interpretation of the Laws. Princeton, NJ: Princeton University Press, 1960.

Patterson, R. Image and Reality in Plato's Metaphysics. Indianapolis, IN: Hackett, 1985.

Robinson, Richard. Plato's Earlier Dialectic. 2nd ed. Oxford: Clarendon Press, 1953.

Ross, W. D. Plato's Theory of Ideas. Oxford: Clarendon Press, 1953.

Santas, G. X. Plato and Freud: Two Theories of Love. Oxford: Blackwell, 1988.

Skemp, J. B. The Theory of Motion in Plato's Later Dialogues. Cambridge, U.K.: Cambridge University Press, 1942.

Solmsen, Freidrich. Plato's Theology. Ithaca, NY: Cornell University Press, 1942.

Stenzel, Julius. Plato's Method of Dialectic. Translated from the 2nd German edition by D. J. Allan. Oxford: Clarendon Press, 1940.

Vlastos, G. Introduction to Plato's Protagoras. New York: Liberal Arts Press, 1956.

Vlastos, G. Platonic Studies. 2nd ed. Princeton, NJ: Princeton University Press, 1981.

Vlastos, G. Studies in Greek Philosophy. Vol. 2. Princeton, NJ: Princeton University Press, 1995.

Wedberg, A. E. C. Plato's Philosophy of Mathematics. Stockholm: Almqvist & Wiksell, 1955.

On Socrates

Gigon, O. Sokrates, sein Bild in Dichtung und Geschichte. Bern: A. Francke, 1947.

Momigliano, A. The Development of Greek Biography Cambridge, MA: Harvard University Press, 1971.

Patzer, A., ed. Der Historische Sokrates. Darmstadt: Wissenschaftliche Buchgellschaft, 1987.

Vlastos, G. Socrates, Ironist, and Moral Philosopher. Cambridge, U.K.: Cambridge University Press, 1991.

On the Early Academy

Dillon, J. The Heirs of Plato: A Study of the Old Academy. Oxford: Clarendon Press, 2003.

Ostwald, M., and J. P. Lynch. "Plato's Academy." Cambridge Ancient History VI, 602–616. 2nd ed. Cambridge, U.K.: Cambridge University Press, 1994.

On the Chronology of the Dialogues

Brandwood, L. The Chronology of Plato's Dialogues. Cambridge, U.K.: Cambridge University Press, 1990.

Campbell, L. The Sophistes and Politicus of Plato. Oxford: Clarendon Press, 1867.

Kahn, C. H. "On Platonic Chronology." New Perspectives on Plato, Modern and Ancient, edited by J. Annas and C. Rowe, 93–127. Cambridge, MA: Harvard University Press, 2002.

Ritter, C. Untersuchungen über Plato. Stuttgart: n.p., 1888.

Bibliographies

Brisson, Luc, and Benoît Castelnérac. Platon, 1995–2000: Bibliographie. Paris: Vrin, 2004.

Brisson, Luc, and Frédéric Plin. Platon, 1990–1995: Bibliographie. Paris: Vrin, 1999.

Cherniss, H. F. "Plato Studies, 1950–1957." Lustrum 4 (1959): 5–308; 5 (1960): 323–648.

Rosenmeyer, T. G. "Platonic Scholarship, 1945–1955." Classical Weekly 50 (1957): 172–182, 185–196, 197–201, 209–211.

Saunders, Trevor, and Luc Brisson. Bibliography on Plato's Laws, revised and completed with an additional Bibliography on the Epinomis by Luc Brisson. Sankt Augustin, Germany: Academia Verlag, 2000.

Charles H. Kahn (2005)