A Heap of Precedents

Julian Sanchez at Reason on Kelo and Raich.

There's a famous philosophical puzzle, originally attributed to Eubulides of Miletus, known as the sorites paradox or heaps problem. It goes like this: Two or three grains of sand obviously don't constitute a "heap" of sand. And it seems absurd to suppose that adding a single grain of sand could turn something that wasn't a heap into a heap. But apply that logic repeatedly as you add one grain after another, and you're pushed to the equally absurd conclusion that 100,000 grains aren't a heap either. (Alternatively, you can run the logic in the other direction and prove that three grains of sand are a heap.)

It's not a terribly deep puzzle, of course: It simply illustrates that some of our everyday concepts, like that of a heap, are vague or fuzzy, not susceptible to such precise definition. Try to define such concepts in too much detail and absurdity results.

The problem is, concepts like "interstate commerce," "public use," "unreasonable search," and "cruel and unusual" are similarly fuzzy. And stare decisis, the principle that cases are to be decided by reference to previous rulings, means that the Court's interpretation of those rulings looks an awful lot like a process of adding one grain at a time without ever arriving at an unconstitutional heap—an instance of what law professor Eugene Volokh has called an "attitude altering slippery slope." Jurisprudence is all about distinguishing cases, explaining why some legal principle applies in situation A, but not in apparently similar situation B. But if the grains are fine enough—the differences from case to case sufficiently subtle—plausible distinctions become harder to find.
[...]
These two decisions prompted outrage not because either was a radical departure from precedent —neither was—but because they called attention to just how many grains of precedent had been piled atop the terms "public use" and "interstate commerce," reaching so far from the common-sense meanings of those terms as to seem preposterous if one is only eyeballing the heap, rather than attending to the process.
[...]
[L]legal rules, to be legitimate, should also reflect a shared public understanding. That's not to say the polls must vindicate each particular court ruling. But when stability begins to undermine the public's sense that they understand the most fundamental rules by which they're governed, it's a sign that jurists need to be willing to step back and see the heap.