ABSTRACT
Aristotle himself associated simplicity with the categories: every simple term falls into just one category. Yet that account, as he recognized, leaves open the possibility of a sort of combination of items from different categories to produce, not a proposition, but a new predicate falling into no one category. For reasons to be considered in Volume II, he provided only one kind of example of such a predicate, in which substance is combined with accident as man is combined with musical to form musician. Like any term, 'musician' asserts nothing by itself, yet its compound nature shows itself in predication. 'John is a musician' means the same as the compound proposition, 'John is a man and John is musical'. 'Musician' is therefore quite different from 'man', since (even if we accept the traditional definition) 'John is a man' does not fall apart as 'John is an animal and John is rational'. On the Aristotelian view, that is because 'Man is a rational animal' is a 'real definition' of the unitary essence or nature of a species. 'Man' classifies the individual according to its nature, placing it in a natural kind. Musicians, by contrast, do not as such belong to a natural kind with a genuine essence, but to a class arrived at by arbitrary combination. Correspondingly musicians are not natural individuals qua musicians but qua human beings.60
