Defeasibility and Pragmatic Indeterminacy in Law

Abstract

In one standard sense, defeasibility is a feature of inferences, and one that seems to defy classical first order logic: An inference is defeasible when its putative conclusion is rendered doubtful by the addition of premises (thus violating monotonicity). The main argument of this paper is that certain types of inferences are defeasible in ways that render the putative conclusion genuinely indeterminate. The discussion, and most of the examples, focus on pragmatic inferences, legal inferences and on some overlapping cases, that is, cases in which legal defeasibility is actually a matter of pragmatics. I also argue that legal presumptions and the open-endedness of possible exceptions to legal rules behave differently, and are not susceptible to the kind of defeasibility discussed here. The upshot of the discussion is to show that defeasibility in law sometimes generates a genuine kind of legal indeterminacy. From a legal point of view, the conclusion would be neither here nor there. In such cases, decision-makers must make their judgments on the basis of considerations not dictated by the relevant law.