Humanist Perspectives: issue 152: he Famous, or Infamous, Slippery Slope

practical philosophy
The Famous, or Infamous, Slippery Slope
by Trudy Govier

It’s alleged that legalizing assisted suicide will lead to legalizing murder, and for that reason we should not legalize assisted suicide. Or, it is feared, such legalization will lead to the de-valuing of the lives of the weak and handicapped, and ultimately to killing and a cult of death. This type of argument is referred to as the slippery slope, and is prominent in many discussions of assisted suicide. Slippery slope arguments go along the following lines: actions of a certain type may seem all right, but if we permit them, we will be led to permit further actions of related types, which are not all right; therefore, we shouldn’t permit the first actions. Doing something that seems legitimate can lead us to do further, apparently similar, things that are not legitimate. Because we need to avoid the illegitimate actions, we should refrain from doing the apparently legitimate ones.

Although slippery slope arguments are taken seriously in some quarters, they have a generally negative reputation among logicians. The label slippery slope is generally used to name a fallacy. Other labels for such arguments include the thin edge of the wedge, the floodgates and the camel’s nose.

Slippery slope arguments occur in many public debates. Readers may recall their prominence in discussions of abortion. Once we have legitimized abortion, won’t we accept infanticide? Where will we draw the line? How can we mark a moral distinction between abortion at ten weeks and abortion at five months?

We also find slippery slope arguments used against same sex marriage. The idea here is that once the law departs from monogamous heterosexual marriage, it will come to include bigamy, polygamy, incest and bestiality.

Many who allege slippery slopes have a recognizable theological perspective. They may use the slippery slope as cover for ideas that find their real source in religious teaching.

Allegedly, permitting same sex marriage will launch us on an unstoppable slide to generalized perversion and social chaos. So although it might be acceptable in its own right, same sex marriage should not be made legal.

The perceived seriousness of slippery slope arguments may vary depending on our political perspective. Few humanist readers will take seriously allegations of general social deterioration due to permitting abortion or same sex marriage. On these topics, many who allege slippery slopes have a recognizable theological perspective. They may use the slippery slope as cover for ideas that find their real source in religious teaching. Nevertheless, slippery slope arguments on other topics may seem more plausible.

Consider, for instance, the idea that a country is justified in going to war on the grounds that it is, pre-emptively, defending itself. (That was claimed by the United States in 2002.) What about this slippery slope argument against the doctrine of pre-emptive defense. ‘If one country claims pre-emptive defense as a legal basis for war, others will do the same. The rationale of pre-emptive defense will come to seem normal and will be widely accepted. States will more readily resort to violence and the ultimate result of this generalized slide will be chaos on the international scene. Therefore the doctrine of pre-emptive defense should not be accepted.’ Given the relationship between international law and the practice of nations, this particular slippery slope may have some credibility.

If we accept one slippery slope argument, are we, by the logic of consistency, required to accept them all? Are we sliding unstoppably down towards mental decline, committed to the acceptance of more and more questionable arguments?

Reasoning by appealing to relevantly similar cases is highly important in law, administration, and ethics. In general, this kind of case-based reasoning is acceptable. It’s referred to as reasoning from precedent. In slippery slope arguments, precedent reasoning is used incorrectly. The problem is that these arguments assume that cases that are legitimate are relevantly similar to other cases that are not legitimate. But if one sort of action is legitimate and another is illegitimate, there must be a relevant difference between them. And there are relevant differences. Think about it. Abortion is relevantly different from infanticide; lesbian marriage is relevantly different from incest; assisted suicide is relevantly different from murder.

Slippery slope arguments assume that people will regard one sort of thing as a precedent for others — despite relevant differences that exist between the cases. The claim underlying the slippery slope is that because they will ignore relevant differences, people will come to endorse illegitimate actions as a result of their acceptance of legitimate ones. Such carelessness will put them (or all of us) on an unstoppable slide to the degenerate bottom of a moral hill.

The claim that differences will not be noticed is a broadly empirical claim. It needs to be supported by evidence. But in most slippery slope arguments, no such evidence is given. Claims that moral slippage is going to occur are undefended at best, and wildly implausible at worst.

In a recent article scheduled to appear soon in the Harvard Law Review, Eugene Volokh questions the idea that slippery slope arguments are fallacious. He suggests that arguers should qualifier their conclusions and claims, and can avoid fallacy by doing that. People should assert not that accepting x will lead to accepting y and z, but rather that accepting x can make accepting y and z more likely. Significantly, Volokh contends that people who argue on the basis of slippery slopes need to show some plausible mechanism by which the moral slippage would occur. Often no such mechanism could plausibly be proposed. Many slippery slope arguments amount to no more than scare tactics. But in some cases, the prospects of slippage and careless appeals to precedent are realistic. Volokh discusses an amazing number of plausible mechanisms, including desensitization, administrative ease, lowered cost, legal precedent, following the crowd, ignorance and limited rationality.

One can hardly deny that following the crowd, ignorance, and limited rationality are real features of human thinking. Do we need to question the standard philosopher’s assumption that slippery slope arguments are fallacious?

Suppose that x is acceptable and that y and z are unacceptable. Now suppose that there is a plausible mechanism explaining why we would be likely to condone y and z once we had accepted x. If all these conditions held, then one consideration against allowing x would be that accepting x may make the acceptance of y and z more likely. Carefully amended and qualified in this way, a slippery slope argument would not be a fallacy. But the amendments allow that it is far from a compelling argument. It only gives one consideration supporting the claim that illegitimate actions might come to be condoned.

We can apply these themes to the question of assisted suicide. The burden of proof is on people who appeal to slippery slope arguments to argue against assisted suicide. They need to buttress their arguments by explaining just how and why people would be led from supporting assisted suicide to supporting the killing of the handicapped and to de-valuing life itself. They then need to recognize that in exploring the likelihood of unintended consequences, they have entered the territory of probabilities and the balancing of pros and cons. At that point, they will enter into a debate with supporters of assisted suicide where they will be engaged in considering reasons, risks and safeguards.

Slippery slope arguers might escape allegations of fallacy — but they can only do that by engaging in realistic debate about attitudes and consequences.

Trudy Govier is a philosopher and author of many books, including Forgiveness and Revenge, Dilemmas of Trust and A Practical Study of Argument.