Abstract: Focuses on two themes in Aristotle's philosophy and their interconnection. The first is his account of the meaning (or signification) of terms such as ‘man’, ‘fish’, and ‘eclipse’, which refer to kinds of objects or processes. The second is his theory of the essences of these kinds, what we refer to in defining them, and what makes them what they are. For Aristotle, the meaning of such terms is determined by a distinctive type of efficient causal connection between the kind and thoughts with which the terms are associated. However, although these terms signify existing kinds with essences, one who has the relevant thoughts need not know either that the kind exists or that, if it exists, it has an essence of a given type. In consequence, Aristotle's account of the essence of kinds has to be grounded in his metaphysics and not in his theory of the mastery of natural kind terms. Aristotle's essences are specified in our definitions of kinds because they determine the kind's distinctive nature and necessary properties. They simultaneously ground the identity of the kind and explain its necessary, but non-essential, features. In these respects, Aristotelian essentialism, which plays a central role in his scientific and metaphysical writings, is distinct both from twentieth-century attempts to revive essentialism (such as are to be found in the writings of Kripke and Putnam) and from the views criticized by anti-essentialists (such as Locke and Quine). This book aims to set out and critically evaluate Aristotle's distinctive form of essentialism.

Keywords: ancient philosophy, Aristotle, biological classification, causal explanation, David Charles, essence, essentialism, explanation, kind term, meaning, natural kinds, philosophy, scientific enquiry, signification