Protagoras is a dialogue by Plato. The traditional subtitle (which may or may not be Plato's) is "or the Sophists". The main argument is between the elderly Protagoras, a celebrated Sophist, and Socrates. The discussion takes place at the home of Callias, who is host to Protagoras while he is in town, and concerns the nature of Sophists, the unity and the teachability of virtue. A total of twenty-one people are named as present.