One can start to make heads and tails of Socrates’s discussion of the unity of virtue with Protagoras once one introduces the concept of moral perfection. Written in 1969, John Passmore’s book, The Perfectibility of Man, remains a touchstone on this subject. Moral perfection, which is but one kind of perfection and which is not to be confused with the seven other kinds he discusses, is to be ‘entirely without moral defect.’ A morally perfect agent acts flawlessly in that he always does the right thing.

What makes it possible for one to always act virtuously? And not so according to the best possible luck or owing to the gods. This is Socrates’s question. He would likely grant Protagoras’s intuitive views that habit and feeling help to cultivate virtues in a young person and that many community members are teachers of some virtue or other in this sense. But that is not what Socrates is after. He wants to discover a teacher who, knowing what virtue is, always acts virtuously and so can teach others to always act virtuously themselves. And so far he has found none and not even, or especially, himself.

It is against this intellectual background of moral perfection that one can make pretty decent sense of Socrates’s Unity of Virtue thesis. In his important paper, ‘The Unity of the Virtues in the “Protagoras,”‘ Gregory Vlastos argues that

1.) If I have one of the virtues, then I have all of the virtues.

2.) Wisdom is a necessary condition for my having any other virtue.

3.) Wisdom is a sufficient condition for my having any other virtue.

So, in the virtuous life wisdom is sovereign. If the question is, ‘How is it possible for me to always (i.e., in any circumstances in which I find myself) act virtuously?,’ the answer is: ‘I must be wise.’ And if I’m wise, then I’m temperate (etc.). And since I’m temperate, I’m also pious, just, and brave.

So far, so good. It is not at all puzzling to conceive of John’s wise justice, his wise temperance, wise courage, and wise piety. Yet what is puzzling is whether each virtue must be instantiated on every occasion. Vlastos says so: ‘Justice is not only wise, but also temperate, brave, and pious.’ Does he mean that one act can be described as wise, temperate, brave, and pious? Or does he mean that on occasion X, justice is justice that it could be temperate justice. I’m not sure which he is saying, but the latter sounds more persuasive.

I am inclined to return to ‘having’ without necessarily instantiating a virtue on a certain occasion. If I have any virtue, then surely I have the rest. But it doesn’t follow that all virtues are instantiated on any given occasion. Of course, a single act could be wise, just, and brave: imagine, given the right circumstances, a general seeking to save a fellow soldier caught behind enemy lines. And there is no reason to doubt that a wisely pious act couldn’t also be temperate. And so on.

Vlastos is right that, for Socrates of the Protagoras, each virtue requires its own definition, wisdom must reign supreme, and all the virtues are connected by means of interentailment. The Socratic morally perfect agent would use his knowledge (i.e., his wisdom) to direct him to act exactly as and how the particular situation requires. The juxtaposition between the fallibilist Socrates who keeps inquiring while knowing that he may be wrong or in error and the morally perfect being who always acts virtuously is a striking image with which to conclude.