The Posterior Analytics is Aristotle’s main account of the nature and structure of scientific explanation. Much of its second book is concerned with scientific explanations of the essences of things. In the standard interpretation of these chapters, Aristotle is chiefly concerned with showing how scientific research moves from a partial understanding of some natural kind to a scientifically adequate understanding of that kind. Mr. Goldin argues against this, showing instead that Aristotle’s main project is the deepening and elaboration of the theory of scientific explanation that is presented in the first book of the Posterior Analytics.