SLIPPERY SLOPE ARGUMENTS

"Partial-birth abortion bans are not themselves that bad. But you should oppose them because, if they are enacted, much broader bans on abortion will become more likely." "Letting dying people cut off their lifesaving treatment may seem proper on its own. But if we allow that, it may lead to dying people getting help in actively killing themselves, and then over time to involuntary killing of the comatose or even of the disabled." "Embryonic stem cell research might be OK in itself, but it may lead to people getting pregnant just to get abortions." Such arguments are commonplace in debates on many ethical topics: abortion, euthanasia, genetic engineering, gun control, free speech, privacy, and more.

All these arguments express concern about the slippery slope: the risk that implementing a seemingly modest and worthwhile decision A now will increase the likelihood of a much broader and more harmful decision B later. The arguments are sometimes made by political liberals and sometimes by political conservatives. They sometimes relate to judicial decisions and sometimes to legislative ones. But they are all prudential arguments about long-term consequences.

The slippery slope is not just a form of argument. It is also an asserted real-world phenomenon—the tendency of one decision to increase the likelihood of others. If this phenomenon is real, people may want to consider it when deciding where to stand on policy questions: After all, if a decision today does make likelier other decisions tomorrow, it is prudent to consider this risk when making the first decision.

Analyzing Slippery Slope Arguments

There is no well-established definition for what constitutes a slippery slope. Some limit it to situations where A and B are separated by a long series of incremental steps: first one restriction on gun ownership, then another, then a third, and eventually all guns are banned. Others limit slippery slopes to situations where A and B cannot be easily logically distinguished. Some philosophers define the slippery slope as a form of purely logical argument, that enacting A will logically require the enactment of B.

Still others look to the reason that people worry about slippery slopes. Voters, legislators, judges, and others often face the question, Should I support proposal A, or should I oppose it for fear that it might help bring about B? To answer this, one must consider all the possible ways that A can help lead to B—whether sudden or gradual, logical or political. This entry will therefore use this broad definition: A slippery slope happens whenever one narrow judicial or political decision now (for instance, banning Nazi or Communist speech) increases the likelihood that another, broader decision will be enacted later (for instance, censorship of more speech).

Not We, but They

Why would slippery slopes ever happen? Say that we think gun registration (A) is good but gun confiscation (B) is bad. Why would decision A make decision B more likely? If we dislike gun confiscation now, would we not dislike it as much even after gun registration is enacted?

Social decisions are made by groups composed of individuals—voters, legislators, judges, and so on—who have different views. The slippery slope concern is that our support for decision A today will lead other people to support decision B tomorrow.

For instance, gun registration may make gun confiscation easier because the police will know where the guns are. It may also make confiscation more defensible legally because the police will be able to get warrants to search the homes of those people who have the guns. The cheaper a policy is, the more likely people are to support it. This year a swing group of voters may help enact gun registration because they like registration but not confiscation. But next year the same group might find itself outvoted by another group of voters who conclude that, because guns are now registered, confiscation is cheaper and thus more appealing.

The first group of voters will have fallen victim to the slippery slope: They voted for a modest step A, which they liked, but as a result got outcome B, which they loathe. They may then wish that they had considered the slippery slope dangers before making the first decision.

Different Slippery Slope Mechanisms

How can one evaluate the likelihood that supporting A will indeed lead others to support B? The metaphor of the slippery slope, unfortunately, will not help, precisely because it is just a metaphor. It is necessary to identify the mechanism behind it: How exactly will the first decision change the conditions under which others will evaluate the second proposal? There are several such mechanisms, all of which can be called slippery slopes, but which are analytically different. Here are just a few examples.

COST-LOWERING SLIPPERY SLOPES. The gun registration example is one scenario. If decision A makes decision B cheaper, then it makes B more likely.

EQUALITY SLIPPERY SLOPES. Decision A may lead some people to feel that decision B must be enacted as well for equality reasons. For instance, some people argue that it is unfair to allow the dying to commit assisted suicide while refusing to permit the same release to those who are in great psychological pain but are not dying. The first step A may push some voters, legislators, or judges to support B, not because they like B as such, but because they oppose discrimination between A and B.

ENFORCEMENT NEED SLIPPERY SLOPES. When a modest restriction A—for instance, a mildly enforced prohibition on some drug—is often violated, some people may come to support a much more severe restriction B (for instance, a war on drugs, with harsh punishments and intrusive searches) because they do not like to see the law being flouted. The intermediate position A thus becomes politically unstable, and slippage to B more likely.

ATTITUDE-ALTERING SLIPPERY SLOPES. Thus far this entry has discussed slippery slopes that operate without changing anyone's underlying attitudes. People might have the same attitudes about equality or cost as they did before A—but once A is enacted, those very attitudes lead them to support B, because of changed real-world circumstances.

Some slippery slopes, though, do operate by changing people's attitudes. Many voters, and even some legislators and judges, feel that they know little about certain issues. For instance, if they are asked whether they support some restriction on privacy, they might realize that privacy questions are very difficult, and that they have no good theory about which restrictions are good and which are not. Because they are thus rationally ignorant—they know the necessary limitations of their own knowledge—they may defer to the judgment of other authoritative institutions, such as courts and legislators. So if some kind of surveillance is legally permitted, many voters may therefore conclude that it is also morally proper.

This means that when proposal A is being considered, one must try to predict not only what A will do on its own terms, but also how it will change public attitudes. Will it, for instance, lead voters to alter their views to the point that they will also start supporting broader proposals like B? Will stem cell research on human embryos, for instance, change people's attitudes about the propriety of harvesting older fetuses or even babies for medical purposes? Would it lead people to think of abortions as a good rather than a necessary evil, and thus legitimize (for instance) people's getting pregnant just to harvest the resulting embryos? This sort of psychological prognostication is difficult, but it often has to be done if people are to decide whether the benefits of A indeed exceed its costs.

LEGISLATIVE-LEGISLATIVE, LEGISLATIVE-JUDICIAL, JUDICIAL-LEGISLATIVE, AND JUDICIAL-JUDICIAL SLIPPERY SLOPES. All these slippery slopes may in some measure operate whether decisions A and B are legislative decisions or judicial ones. Slippery slopes are often associated with judicial decision making, in which the doctrine of precedent helps accelerate the slide chiefly by strengthening the equality slippery slope and the attitude-altering slippery slope. But as some of these examples show, slippery slopes can operate even without any formal rule of precedent.

The Slippery Slope Inefficiency

None of these arguments, of course, always carry the day—nor should they. Sometimes we must make decisions even if there is a risk that the decisions will lead others to enact laws of which we disapprove. And yet some policy proposals that may be good on their own do end up being blocked because of eminently reasonable slippery slope concerns; one might call this the slippery slope inefficiency. Some people think this is true of gun registration, which has been blocked by concerns over a slippery slope to gun confiscation. Others think it is true of moderate assisted suicide proposals, which may be blocked by concerns that assisted suicide will become the norm for more and more patients.

Identifying this inefficiency suggests, perhaps surprisingly, that constitutional rights might sometimes enable modest regulation even while they disable broader prohibition. If gun right supporters feel that their right to own guns is constitutionally secure and, thus, that gun confiscation would be struck down by the courts, many of them might well drop their opposition to gun registration—an opposition that may be largely driven by slippery slope risks. If a trustworthy barrier against slippage is erected, then people may be more willing to take the first step out onto the slope.

EUGENE VOLOKH

SEE ALSO Choice Behavior;Decision Theory.

BIBLIOGRAPHY

Rizzo, Mario J., and Douglas Glen Whitman. (2003). "The Camel's Nose Is in the Tent: Rules, Theories, and Slippery Slopes." UCLA Law Review 51(2): 539–592.

Schauer, Frederick. (1985). "Slippery Slopes." Harvard Law Review 99(2): 361–383.

Volokh, Eugene. (2003). "Mechanisms of the Slippery Slope." Harvard Law Review 116(4): 1026–1137.

Walton, Douglas. (1992). Slippery Slope Arguments. New York: Oxford University Press.