Aristotle was a systematic writer who often cross-referred to the definitions of terms given elsewhere in his work. Book 5 of the <i>Metaphysics </i>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. <br/>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 <i>Metaphysics</i> as a whole.