<em>The Logic of Essentialism</em> surveys the major interpretations, ancient, medieval and modern, of Aristotle's Modal Syllogistic. It presents a framework within which these competing interpretations are compared and evaluated. A new interpretation is developed, which agrees in large measure with Aristotle's text, including his theses, methods of proof, and use of examples. This interpretation reads Aristotle's modal sentences <em>de re</em>, and attaches considerable importance to his use of <em>ecthesis</em> and counter-examples. It features a formal semantic analysis that makes no reference to possible worlds, and it articulates the links, both theoretical and genetic, between the modal syllogistic and Aristotle's essentialist metaphysics.