Abstract
At the beginning of the first book of Posterior Analytics, Aristotle‟s feature of demonstrative knowledge involves a certain concept of “necessity”. The traditional interpretation tends to associate this concept with modal necessity, which is found in the Prior Analytics and De interpretatione. The present article aims to show in which way the sixth chapter of book A of Posterior Analytics presupposes a set of essentialist theses that claims to base the necessity of scientific knowledge on predicative relations of essential character. To acknowledge this essentialist background and simultaneously support a modal interpretation of scientific necessity urges us to attribute serious drawbacks to Aristotle‟s theory of demonstration, forcing us to reassess this interpretative tendency