Julian makes the excellent point that precedent-based decisionmaking in the presence of vague terms can lead to a slippery slope. I consider this point excellent, of course, because Mario Rizzo and I said essentially the same thing in our article, “The Camel’s Nose Is in the Tent: Rules, Theories, and Slippery Slopes” (see section III for the relevant analysis).
The bigger picture is that precedent is a double-edged sword: Precedent can constrain, but it can also enable. In the vagueness-slope described by Julian, a sequence of small marginal decisions eventually leads to applications of an idea (e.g., a rule or term) in circumstances radically different from those of the original case. Without the intermediate precedents, the decisionmaker would be unable to reach the undesirable conclusion in the present case; the intervening precedents enable the bizarre outcome. But it’s not hard to think of other processes in which precedent-based decisionmaking plays an enabling role.
One such process is what Mario and I dub the “Humean beneficence process” (see section IV-C). This is a reference to David Hume’s observation that beneficence is a concrete virtue: people tend to be most forgiving and beneficent toward others when they are faced with concrete circumstances – e.g., a destitute neighbor, a starving baby, or a sympathetic plaintiff. Justice, on the other hand, is an abstract virtue whose desirability typically lies in the overall system it creates, rather than the particular circumstances of any given case. A tension between the two arises because judges are asked to apply abstract rules of justice to concrete cases. In many individual cases, they may be tempted to depart from the usual rules of justice in the name of pity or compassion. For instance, the judge may wish to make an insurance company pay damages to a poor individual to cover his significant medical costs, even if those costs were not plausibly caused by the insurance company’s client.
That temptation alone would not be sufficient to create a slippery slope. The problem arises from the fact that any exception-making decision can serve as a precedent for future decisions. We can imagine that, early on in the process, adherence to precedent would generally constrain most judges. Seeing few if any exception-making precedents, their benevolence is held in check and they follow the general rule. But if one or two judges are tempted strongly enough, they may indulge their benevolent impulses and make exceptions. Future judges, facing similar temptations, will now have a stronger legal basis for doing likewise. Exception-making decisions accumulate further, so that eventually precedent enables change as much or more than it impedes it. The long-run effect is the erosion of bright-line rules in favor of vague balancing rules.