As we have explained, the common law develops from specific narrow rules to broader precepts, a classic process of inductive reasoning. Yet, to understand induction, it is best to first learn deduction. Hence we put the deductive cart before the inductive horse with some introductory observations on deductive reasoning. Formal deductive logic is an act of the mind in which, from the relation of two propositions to each other, we infer, that is, we understand and affirm, a third proposition. In deductive reasoning, the two propositions which imply the third proposition, the conclusion , are called premises.
Logical argument is a means of determining the truth or falsity of a purported conclusion.
We do this by following well established canons of logical order in a deliberate and intentional fashion. In law we must think and reason logically. We must follow a thinking process that emancipates us from impulsively jumping to conclusions, or frees us from argument supported only by strongly felt emotions or superstitions. The classic means of deductive reasoning is the syllogism. Special rules of the syllogism serve to inform exactly under what circumstances one proposition can be inferred from two other propositions.