One of my favorite daily reads is the Volokh conspiracy, a blog by a group of law professors. As one would expect, their arguments are exquisitely reasoned, honed by years of classroom teaching, academic writing, and litigation. Although they have a definite philosophical point of view (libertarian), these scholars apply the law with intellectual integrity, developing their arguments logically from existing law and precedent. However, I cannot help but wonder about the use of logic in law.
In formal logic, the starting point is an axiomatic system, a set of statements assumed as true (axioms) that defines a particular field. The rules of logic are then used to derive theorems within that field. The most famous example is the field of Euclidean geometry, which is built upon Euclid's axioms. When developing an axiomatic system, mathematicians want a system that is consistent, independent, and complete. For our purposes here, we can ignore independence and completeness. The crucial property is consistency: axioms within an axiomatic system should not contradict one another.
Legal analysis applies the rules of logic (for example, A implies B, B implies C, hence A implies C), but it does so outside of anything resembling an axiomatic system. Laws, statutes, and precedents vaguely resemble axioms in the sense that they are assumed to be true. But the legal system is rife with contradictions. When an axiomatic system is not consistent, it contains at least one statement that is simultaneously true and false, and from that statement one can derive an unlimited number of other statements that are simultaneously true and false. In law, one can reduce the inconsistencies by only considering those laws that are deemed relevant to a particular case. No matter which subset of laws one gets to work with, it is virtually impossible for it to be anywhere near a consistent axiomatic system. Formal logic seems doomed in legal reasoning.
In spite of their mutual resemblance, legal logic lives in a universe quite different from formal logic. Legal logic is about convincing others of the merits of a case. A legal argument is successful only if accepted by some authority, and this acceptance lasts only until a higher authority overturns it. With every decision, legal authorities help shape the nature of successful legal argument. This creates a legal logic that evolves over time and reflects the nature of the power of the state. The law is about power, not logic... Who knew?