show us pleasures and pains in their true proportion. This art of
mensuration is a kind of knowledge, and knowledge is thus proved once more
to be the governing principle of human life, and ignorance the origin of
all evil: for no one prefers the less pleasure to the greater, or the
greater pain to the less, except from ignorance. The argument is drawn out
in an imaginary 'dialogue within a dialogue,' conducted by Socrates and
Protagoras on the one part, and the rest of the world on the other.
Hippias and Prodicus, as well as Protagoras, admit the soundness of the
conclusion.

Socrates then applies this new conclusion to the case of courage--the only
virtue which still holds out against the assaults of the Socratic
dialectic. No one chooses the evil or refuses the good except through
ignorance. This explains why cowards refuse to go to war:--because they
form a wrong estimate of good, and honour, and pleasure. And why are the
courageous willing to go to war?--because they form a right estimate of
pleasures and pains, of things terrible and not terrible. Courage then is
knowledge, and cowardice is ignorance. And the five virtues, which were
originally maintained to have five different natures, after having been
easily reduced to two only, at last coalesce in one. The assent of
Protagoras to this last position is extracted with great difficulty.

Socrates concludes by professing his disinterested love of the truth, and
remarks on the singular manner in which he and his adversary had changed
sides. Protagoras began by asserting, and Socrates by denying, the
teachableness of virtue, and now the latter ends by affirming that virtue
is knowledge, which is the most teachable of all things, while Protagoras
has been striving to show that virtue is not knowledge, and this is almost
equivalent to saying that virtue cannot be taught. He is not satisfied
with the result, and would like to renew the enquiry with the help of