many?' To which Protagoras is now disposed to reply, that four out of the
five virtues are in some degree similar; but he still contends that the
fifth, courage, is unlike the rest. Socrates proceeds to undermine the
last stronghold of the adversary, first obtaining from him the admission
that all virtue is in the highest degree good:--

The courageous are the confident; and the confident are those who know
their business or profession: those who have no such knowledge and are
still confident are madmen. This is admitted. Then, says Socrates,
courage is knowledge--an inference which Protagoras evades by drawing a
futile distinction between the courageous and the confident in a fluent
speech.

Socrates renews the attack from another side: he would like to know
whether pleasure is not the only good, and pain the only evil? Protagoras
seems to doubt the morality or propriety of assenting to this; he would
rather say that 'some pleasures are good, some pains are evil,' which is
also the opinion of the generality of mankind. What does he think of
knowledge? Does he agree with the common opinion that knowledge is
overcome by passion? or does he hold that knowledge is power? Protagoras
agrees that knowledge is certainly a governing power.

This, however, is not the doctrine of men in general, who maintain that
many who know what is best, act contrary to their knowledge under the
influence of pleasure. But this opposition of good and evil is really the
opposition of a greater or lesser amount of pleasure. Pleasures are evils
because they end in pain, and pains are goods because they end in
pleasures. Thus pleasure is seen to be the only good; and the only evil is
the preference of the lesser pleasure to the greater. But then comes in
the illusion of distance. Some art of mensuration is required in order to