Simplicius' commentary on Aristotle's "Categories" falls into two parts. First, it examines the six categories dealt with in chapter 9 of "Categories", namely acting, undergoing, being in a position, when, where, and having. Secondly, it examines the so-called "Postpraedicamenta" consisting of chapter 10-15, which treat four kinds of opposition (relatives, contraries, possession, and privation, affirmation and negation), along with priority, simultaneity, movement and (again) having.