the ruler was not infallible but might be sometimes mistaken.

You argue like an informer, Socrates. Do you mean, for example, that
he who is mistaken about the sick is a physician in that he is
mistaken? or that he who errs in arithmetic or grammar is an
arithmetician or grammarian at the me when he is making the mistake, in
respect of the mistake? True, we say that the physician or
arithmetician or grammarian has made a mistake, but this is only a way
of speaking; for the fact is that neither the grammarian nor any other
person of skill ever makes a mistake in so far as he is what his name
implies; they none of them err unless their skill fails them, and then
they cease to be skilled artists. No artist or sage or ruler errs at
the time when he is what his name implies; though he is commonly said
to err, and I adopted the common mode of speaking. But to be perfectly
accurate, since you are such a lover of accuracy, we should say that
the ruler, in so far as he is the ruler, is unerring, and, being
unerring, always commands that which is for his own interest; and the
subject is required to execute his commands; and therefore, as I said
at first and now repeat, justice is the interest of the stronger.

Indeed, Thrasymachus, and do I really appear to you to argue like an
informer?

Certainly, he replied.

And you suppose that I ask these questions with any design of injuring
you in the argument?

Nay, he replied, 'suppose' is not the word--I know it; but you will be
found out, and by sheer force of argument you will never prevail.

I shall not make the attempt, my dear man; but to avoid any
misunderstanding occurring between us in future, let me ask, in what
sense do you speak of a ruler or stronger whose interest, as you were
saying, he being the superior, it is just that the inferior should
execute--is he a ruler in the popular or in the strict sense of the
term?

In the strictest of all senses, he said. And now cheat and play the
informer if you can; I ask no quarter at your hands. But you never
will be able, never.

And do you imagine, I said, that I am such a madman as to try and
cheat, Thrasymachus? I might as well shave a lion.

Why, he said, you made the attempt a minute ago, and you failed.

Enough, I said, of these civilities. It will be better that I should
ask you a question: Is the physician, taken in that strict sense of
which you are speaking, a healer of the sick or a maker of money?