Understanding “what something is” is a project that has long occupied philosophers. Perhaps no thinker in the Western tradition has had more influence on how we approach this question than Aristotle, whose Metaphysics remains the locus classicus of rigorous examinations into the nature of being. Now, in an elegantly argued new study, Aryeh Kosman reinterprets Aristotle’s ontology and compels us to reexamine some of our most basic assumptions about the great philosopher’s thought.

For Aristotle, to ask “what something is” is to inquire into a specific mode of its being, something ordinarily regarded as its “substance.” But to understand substance, we need the concept of energeia—a Greek term usually translated as “actuality.” In a move of far-reaching consequence, Kosman explains that the correct translation of energeia is not “actuality” but “activity.” We have subtly misunderstood the Metaphysics on this crucial point, says Kosman. Aristotle conceives of substance as a kind of dynamic activity, not some inert quality. Substance is something actively being what it is.

Kosman demonstrates how this insight significantly alters our understanding of a number of important concepts in Aristotelian thought, from accounts of motion, consciousness, and essence to explanations of the nature of animal and divine being. Whether it is approached as an in-depth introduction to Aristotle’s metaphysics or as a highly original reassessment sure to spark debate, there can be no argument that The Activity of Being is a major contribution to our understanding of one of philosophy’s most important thinkers.

Virtues of Thought is an excursion through interconnecting philosophical topics in Plato and Aristotle, under the expert guidance of Aryeh Kosman. Exploring what these two foundational figures have to say about the nature of human awareness and understanding, Kosman concludes that ultimately the virtues of thought are to be found in the joys and satisfactions that come from thinking philosophically, whether we engage in it ourselves or witness others’ participation.

Kosman examines Aristotle’s complex understanding of the role that reason plays in practical choice and moral deliberation, and the specific forms of thinking that are involved in explaining the world and making it intelligible to ourselves and others. Critical issues of consciousness and the connection between thinking and acting in Aristotle’s philosophical psychology lead to a discussion of the importance of emotion in his theory of virtue. Theories of perception and cognition are highlighted in works such as Aristotle’s Posterior Analytics. When his focus turns to Plato, Kosman gives original accounts of several dialogues concerning Plato’s treatment of love, self-knowledge, justice, and the complex virtue known as sophrosyne in such texts as Charmides and the Republic.

Bringing together in a single volume previously unpublished essays along with classics in the field, Virtues of Thought makes a significant contribution to our study of ancient Greek philosophy.