Whereas the Prior Analytics derives the theorems of a science from its axioms, the Posterior Analytics is concerned with the nature of the axioms themselves, and hence the general form of an axiomatized deductive science. A science is meant to systematize our knowledge of its subject-matter, so its component axioms and theorems must be propositions which are known and satisfy the conditions set upon knowledge. ‘Knowledge’ reveals these. The first condition is one of causality. Clearly, the axioms must be true. Equally clearly, they must be ‘immediate and primary’. The axioms must be ‘more known’ than the theorems and, finally, they must be ‘prior to and causes of the conclusion’.