The Common Law and the Forms of Reasoning

The purpose of this article is to examine how various forms of reasoning both can and should be used to decide cases in the common law tradition. I start by separating positive questions about what the law is from normative questions about what the law ought to be. Next, I present a Peircean account of three main forms of reasoning – deduction, induction and abduction – and examine how they can be used by judges to decide cases in the common law. Finally, I argue that the three forms of reasoning can be used to answer both kinds of questions, but in different ways. All three forms of reasoning can be used to answer questions of positive law, while questions of normative law present a special case that may require the use of aesthetic judgments of taste in the formation of a legal hypothesis.