Slippery Slope Arguments: Conclusion

[For the last month, I've been serializing my 2003 Harvard Law Review article, The Mechanisms of the Slippery Slope, and I'm finishing it up this week.]

Sandra Starr, vice chairwoman of the Princeton Regional Health Commission …, said there is no "slippery slope" toward a total ban on smoking in public places. "The commission's overriding concern," she said, "is access to the machines by minors."

—New York Times, Sept. 5, 1993, § 1, at 52.

Last month, the Princeton Regional Health Commission took a bold step to protect its citizens by enacting a ban on smoking in all public places of accommodation, including restaurants and taverns…. In doing so, Princeton has paved the way for other municipalities to institute similar bans ….

—The Record (Bergen County), July 12, 2000, at L7.

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Let me return to the question with which this article began: When should you oppose one decision A, which you don't much mind on its own, because of a concern that it might later lead others to enact another decision B, which you strongly oppose?

One possible answer is "never." You should focus, the argument would go, on one decision at a time. If you like it on its own terms, vote for it; if you don't, oppose it; but don't worry about the slippery slope. And in the standard first-order approximation of human behavior, where people are perfectly informed, have firm, well-developed opinions, and have single-peaked preferences, slippery slopes are indeed unlikely. People decide whether they prefer 0, A, or B, and the majority's preferences become law without much risk that one decision will somehow trigger another.

Likewise, in such a world, law has no expressive effect on people's attitudes, people's decisions are context-independent, no one is ignorant, rationally or not, and people make decisions based on thorough analysis rather than on heuristics. Policy decisions in that world end up being easier to make and to analyze.

But as behavioral economists, norms theorists, and others have pointed out, that is not the world we live in, even if it is sometimes a useful first-order approximation. The real world is more complex, and this complexity makes possible slippery slopes and their close relative, path dependence. We can't just dismiss slippery slope arguments as illogical or paranoid, though we can't uncritically accept them, either.

The slippery slope is in some ways a helpful metaphor, but as with many metaphors, it starts by enriching our vision and ends by clouding it. We need to go beyond the metaphor and examine the specific mechanisms that cause the phenomenon that the metaphor describes—mechanisms that connect to the nature of our political institutions, our judicial process, and possibly even human reasoning.

These mechanisms and their effects deserve further study, even if paying attention to them will make policy analysis more complex. So long as our support of one political or legal decision today can lead to other results tomorrow, wise judges, legislators, opinion leaders, interest group organizers, and citizens have to take these mechanisms into account.