Is Defeasibility an Essential Property of Law?*

Abstract

Defeasibility is widespread in law. Lawmakers are not omniscient, and accordingly cannot reliably foresee what the future will bring. Situations will thus arise that were not anticipated, and often could not have been anticipated by even the best of lawmakers. This imperfect view of the future is part of the human condition, and as a consequence legal rules, if literally or faithfully followed, will sometimes generate outcomes that are absurd, silly, unfair, unjust, inefficient, or in some other way suboptimal. When such unfortunate consequences occur as a result of the inevitable overand underinclusiveness of rules, advanced legal systems commonly provide a mechanism by which legal decision-makers may ameliorate the harsh consequences of necessarily coarse rules. But is it necessary that legal systems do so? Is a legal system that fails to do so not a legal system at all, or less of a legal system, or a defective legal system, because of that failure? To put the question directly, is defeasibility necessary to legality? I have argued previously that the defeasibility of legal rules does not necessarily follow from the defeasibility of language, but even if my argument is sound, defeasibility may still emerge as the necessary consequence not of the nature of language, and not of the nature of rules, but of the nature of law. But does it? Is global defeasibility – the defeasibility of all of the rules of a legal system an essential component of any non-defective legal system? That is the question that motivates this paper.