Abstract: In the Protagoras Socrates argues that akrasia is impossible and virtue is knowledge of goodness. In contrast, in the Republic he argues in effect that virtue is the harmony of the parts of the soul, and he seems to take the possibility of akrasia for granted. Despite these differences, I argue that we can trace a gradual development in Socrates' views in these dialogues. In Chapter One, I argue that Socrates' identification of virtue and knowledge in the Protagoras has some counterintuitive implication with the assumption of the dichotomy of virtue/knowledge and vice/ignorance, together with some further assumptions about the teachability of virtue. In the Meno, I argue, Socrates solves this difficulty by introducing virtue as true belief, people who act outstandingly but cannot teach their virtue are virtuous because of their true belief about goodness. In Chapter Two, I argue that Socrates' commitment to hedonism in his argument against akrasia in the Protagoras is only dialectical, and that he gives the reader enough hints to reconstruct his argument without hedonism (but only with the unity of goodness). I also argue that Socrates is committed to what I call a strong version of psychological agathism: the thesis that everyone does what he/she believes to be best overall in the given situation. In Chapter Three, I argue that Socrates in the Republic still maintains the basic tenet of psychological agathism: that every agent does what the agent believes to be good in some way. I examine his theory of the tripartite soul and argue that the parts of the soul are agent-like parts, and a weaker form of psychological agathism applies to these parts. In Chapter Four, I examine Socrates' characterization of the three parts of the soul as the wisdom-loving, the honor-loving, and the money-loving part. I argue that they are characterized in that way in accordance with the objects they would pursue when and if they should function relatively well. With these characterizations, the virtue of the wisdom-lover as well as the limited excellence of the honor-lover and the money-lover can be explained.