Simplicius' commentary on Aristotle's Categories is the most comprehensive philosophical critique of the work ever written, representing 600 years of criticism. In his Categories, Aristotle divides what exists in the sensible world into ten categories of Substance, Quantity, Relative, Quality and so on.. Simplicius starts with a survey of previous commentators, and an introductory set of questions about Aristotle's philosophy and about the Categories in particular. The commentator, he says, needs to present Plato and Aristotle as in harmony on most things. Why are precisely ten categories...