Protagoras provides what is probably the best exposition of a central doctrine of Socratic philosophy: that virtue is knowledge, and that evil is merely another name for ignorance. This makes comprehensible the immense importance Socrates (and also Plato) grants to the subject of education. If virtue is knowledge, then education—the instruction of youth—is, in a very real sense, the creation or destruction of virtuous souls. One of the key arguments of Protagoras consists of a re-examination of what is entailed in the experience commonly referred to as being overcome by pleasure. Socrates argues that the idea that pleasure can dissuade one from doing what one knows to be right is absurd, for what is right is always what is most pleasurable. Knowledge (or virtue) is then the ability to perceive what will bring most pleasure.

There is a strange inconsistency in the progression through these concepts: the analysis of virtue demands an analysis of knowledge; Socrates's consideration of knowledge states that knowledge is an awareness of how to attain pleasurable ends. But this seems to require the further step of examining precisely what these pleasurable ends are. What people take pleasure in is clearly not a constant thing. Socrates's arguments place a great deal of conceptual weight on the notion of pleasure, but this notion remains unexamined. But this failure to complete the course of reasoning is characteristic of Socrates, and occurs repeatedly in Protagoras. Indeed, even the analysis of knowledge is rather incomplete: Socrates does not adequately differentiate what he means by knowledge from what Protagoras means by the kinds of knowledge he claims to be able to teach at the beginning of the dialogue.

However, this pattern of absences does not entail that Protagoras is in any way a badly written philosophical text. Rather, it points to a conception of knowledge as a process, not as something that can be abstracted from life and written down once and for all. If we can learn the knowledge of virtue from Protagoras, we cannot learn it by waiting for Socrates to provide us with all the answers. The unfinished arguments, apparent contradictions and absent conceptual explanations are in fact the spaces in this dialogue from which true knowledge can be acquired.