The unity of the soul in Plato’s Republic

Introduction In Book Four of Plato's Republic, Socrates divides the soul. He argues that because one thing cannot do or undergo opposites in the same respect, in the same relation, and at the same time, some cases of psychological conflict can only be explained by supposing that the soul is actually more than one thing. But Socrates does not deny that the soul is a unity. Rather, he holds that the soul, like so many entities, is both a many and a one. He refers to the divisions as parts of the soul, and even when he ascribes actions and attitudes to a part of the soul, he also ascribes them to the whole soul (esp. 439a--b, 439d). Although few souls enjoy the unity that virtue earns, every human soul possesses an unearned unity. What explains this unearned unity? How do reason, spirit, and appetite constitute a single whole? This question has received little attention. My first aim here is to establish that it is an important puzzle, and my second is to venture an answer.