Paul Ziche

The notion of a µéσον, formally defined as the »middle term« in a syllogism, plays a pivotal role in Aristotle’s theory of scientific demonstrations ( πóδειξις) in his Analytica Posteriora. It is via the µéσον that the distinctive traits of a demonstration – the employment of causal notions and of statements concerning the essence of things – enter into demonstrative syllogisms. This, however, raises problems with respect to the provability of statements concerning the essence of things that Aristotle seems to accept in certain passages of the Analytica Posteriora, as opposed to well-known passages in the Metaphysics. It is shown in which sense essences are in fact demonstrated by their being employed – via the µéσον – in a demonstration, without, however, being mentioned in the conclusion of such a demonstration. The importance Aristotle ascribes to the µéσον in Analytica Posteriora suggests a more flexible, less formalistic understanding of Aristotle’s view of science, while still being based on an analysis of the formal structure of the syllogism.