Protagoras responds to Socrates's challenge (how can virtue be taught) by telling a story about the creation of the animals by the gods. The gods entrust Prometheus and Epimetheus to distribute to these animals their appropriate capabilities. Epimetheus goes first, and doles out various attributes to defend each species from the predations of the others. Next, he provides the animals with different methods of protection from environmental elements and with different sources of food. Finally, he establishes the fertility rate of each animal to be consistent with all these qualities. By distributing different characteristics and faculties to the animals, Epimetheus distributes the different kinds of animals so as to ensure the survival of each kind.
When Prometheus inspects Epimetheus's work, however, he discovers that Epimetheus has left humans "unclothed, unshod, unbedded, unarmed" (321c). Prometheus therefore distributes practical wisdom (the knowledge of fire and of the means of procuring sustenance) amongst humans. But humans live as scattered individuals, defenseless against wild animals, because they have not come together as a community to fight off predators. Zeus therefore dispenses the notions of respect and justice to all humans, enabling them to live together in communities. Communities cannot function if only some members know how to live in a community; hence, the civic arts are distributed universally. Further, Zeus orders a law regulating social behavior: those who do not conform to social norms are to be killed. Certain types of skills (those relating to basic livelihood) are therefore possessed only by some, but the civic virtues (politike arete) are possessed by all. The Athenian political system, Protagoras concludes, is based on the recognition of just this fact.
Having reached this position, Protagoras continues on the subject of punitive justice: to punish a wrongdoer for a past deed is illogical, for the punishment cannot undo the crime. Juridical punishment is therefore oriented towards the future, aiming to alter the behavior of misguided citizens by instilling in them the requisite qualities of justice, piety, and so on. The notion that civic virtue is teachable therefore lies at the foundation of the Greek social order, in the institutional form of the principle that citizens can be changed for the better.
Finally, Protagoras responds to Socrates's claim that virtuous fathers do not teach their sons how to be virtuous. Socrates is factually incorrect, Protagoras asserts: all familial discipline aims at instilling virtue, and this process continues once the child enters formal schooling. The educational mechanism of the system of criminal justice is also at work in these more intimate domains. Civic virtue is like one's mother tongue: one does not need to be taught it, because it is learnt through living within a community. Some, however, are better than others at "showing the way to virtue" (328a); and Protagoras claims that he is one of these people who can show the way.
When he asks them whether they want to hear him argue in the mode of a story or of a logical argument, Protagoras relinquishes an important choice to his listeners in formulating his demonstration that virtue is teachable. In separating so sharply what he wishes to argue from the rhetorical form of that argument (thus divorcing his theory from the expression of that theory) Protagoras embodies an attitude of unconcern and disregard for the true importance of philosophy. This attitude is characteristic of the Sophists, at least as they are represented in Plato's dialogues. For Plato, the form an argument takes should be dictated by the requirements and merits of that argument. In the previous section, Protagoras emphasized that he, unlike other Sophists, did not hide his doctrine beneath appearance but stated it plainly and publicly. Here, by deferring to his audience's wishes, he behaves as if his doctrine is indeed all about appearance, and as if this appearance can be changed to suit whomever he presents it to.
If choosing one's words so that they most faithfully and rigorously express one's meaning is a virtue (and Plato would argue that this is indeed the case), then Protagoras is paradoxically being virtuous by allowing his audience to make his choice for him. The only actual evidence he provides that virtue is indeed teachable is the cultural difference between Greeks and others. Even the wickedest Greek is more virtuous than those who "lack education, and law courts and laws" (327d); this difference, Protagoras asserts, suggests that Greeks have been taught to be virtuous. Therefore, if virtue is a function of society, then by asking his audience (a society in microcosm) how he should argue, Protagoras is indeed uniting the form of his argument with the matter that he is arguing.