Abstract
The central notion of Aristotle's metaphysical system is his concept of substance, which he explicates by means of a number of technical concepts, one of which is being prior in being. Unfortunately, the interpretation of priority in being has proven particularly controversial. In the Categories and the Metaphysics, Aristotle claims that compound substances can be without things in other categories and not vice versa. If we adopt an existential interpretation of the verb ‘to be’ in these claims, it is hard to see how they can be defended. However, alternative interpretations fall prey to a number of objections, especially that they risk conflating priority in being with priority in definition.