First published Thu Oct 23, 2003; substantive revision Wed Apr 22, 2009
Ancient philosophical theories of soul are in many respects sensitive to ways of speaking and thinking about the soul [psuchê] that are not specifically philosophical or theoretical. We therefore begin with what the word ‘soul’ meant to speakers of Classical Greek, and what it would have been natural to think about and associate with the soul. We then turn to various Presocratic thinkers, and to the philosophical theories that are our primary concern, those of Plato (first in the Phaedo, then in theRepublic), Aristotle (in the De Anima or On the Soul), Epicurus, and the Stoics. These are by far the most carefully worked out theories of soul in ancient philosophy. Later theoretical developments — for instance, in the writings of Plotinus and other Platonists, as well as the Church Fathers —are best studied against the background of the classical theories, from which, in large part, they derive.
Adopting a bird's-eye view of the terrain that we will be covering, and setting many details aside for the moment, we can describe it as follows. From comparatively humble Homeric beginnings, the word‘soul’ undergoes quite remarkable semantic expansion in sixth and fifth century usage. By the end of the fifth century— the time of Socrates' death — soul is standardly thought and spoken of, for instance, as the distinguishing mark of living things, as something that is the subject of emotional states and that is responsible for planning and practical thinking, and also as the bearer of such virtues as courage and justice. Coming to philosophical theory, we first trace a development towards comprehensive articulation of a very broad conception of soul, according to which the soul is not only responsible for mental or psychological functions like thought, perception and desire, and is the bearer of moral qualities, but in some way or other accounts for all the vital functions that