Posterior Analytics

A treatise in two books, part of the Organon, on what scientific knowledge is and how it is reached. It opens by saying that all teaching and learning start from knowledge already held. To know something scientifically is to know its cause and that it could not be otherwise, and such knowledge comes through demonstration: a deduction from premises that are true, primary and immediate, better known than and prior to the conclusion, and explanatory of it. Aristotle distinguishes knowing that something is so from knowing why, and argues against both an infinite regress of proofs and circular proof: not everything can be demonstrated, so first principles must be known in another way. Book II relates definition to demonstration and shows how the middle term of a deduction identifies a cause. The last chapter explains how first principles are grasped: perception leads to memory and experience, and by induction we reach the universal, like a rout in battle halted as one soldier after another makes a stand.

It is the first theory of scientific explanation and of how knowledge rests on foundations, and the regress argument it answers still drives debates in epistemology.