Latin. A Latin derivative meaning first. From what is before. By the prior reason. In logic. An argument proceeding from causes to effects. From the past; from what has previously transpired. Under the law, this means the process of deducing facts that follow from general principles or accepted truths; because these facts are true than these other facts must follow.
- (Logic) Characterizing that kind of reasoning which deduces consequences from definitions formed, or principles assumed, or which infers effects from causes previously known; deductive or deductively. To argue or reason by deduction that because certain facts exist, certain other facts will necessarily follow as a consequence. The reverse of a posteriori.
- (Philos.) Applied to knowledge and conceptions assumed, or presupposed, as prior to experience, in order to make experience rational or possible. A priori, that is, form these necessities of the mind or forms of thinking, which, though first revealed to us by experience, must yet have preexisted in order to make experience possible.