The Clarendon Aristotle Series is designed for both students and professionals. It provides accurate translations of selected Aristotelian texts, accompanied by incisive commentaries that focus on philosophical problems and issues. The volumes in the series have been widely welcomed and favourably reviewed. Important new titles are being added to the series, and a number of well-established volumes are being reissued with revisions and/or supplementary material. This volume presents a new translation by Thomas Kjeller Johansen of Aristotle's Metaphysics Books A and a, a signature text within Aristotle's writings, of immense importance for the formation of Western metaphysics and for our understanding of early Greek philosophy. Aristotle's Metaphysics was the first work to define metaphysics as a distinct discipline, the study of the principles of being. When philosophers today discuss the basic questions of being in terms of categories, matter and structure, parts and wholes, identity and continuity, powers and actualities, causes and effects, necessity and contingency, they are pursuing questions first clearly articulated and brought together in Aristotle's Metaphysics. Book A introduces metaphysics or 'wisdom' as the study of first principles and explains why we should pursue it. Aristotle sets out the views of his predecessors and shows that, while they recognised one or more of the four causes, no-one understood any or all of them with sufficient clarity. In Book a, Aristotle further explores the status of the four causes as first principles, explains why it is so difficulty to achieve knowledge of them, and sets out the sorts of accuracy we should expect of various kinds of disciplines. This volume provides a commentary exploring the details of Aristotle's argumentation and its philosophical significance, along with an introduction to Books A and a, explaining their place within the Metaphysics and Aristotle's philosophy as a whole.