Aristotle was a systematic writer who often cross-referred to the definitions of terms given elsewhere in his work. Book 5 of the Metaphysics is important because it consists of definitions of the main uses of key terms in Aristotle's philosophy, and it is extremely valuable to have a commentary on this important text by Alexander of Aphrodisias, the leading commentator of his school. Alexander provides a detailed commentary on all of the thirty terms analysed in Book 5, weighing alternative interpretations of what Aristotle says one against another, defending Peripatetic views against actual and possible criticisms, and attempting to integrate what is said in Book 5 into the context of the Metaphysics as a whole.