Soc. Suppose I tell you something which somebody who knows told me.

Phaedr. Certainly.

Soc. May not "the wolf," as the proverb says, claim a hearing"?

Phaedr. Do you say what can be said for him.

Soc. He will argue that is no use in putting a solemn face on these matters, or in going round and round, until you arrive at first principles; for, as I said at first, when the question is of justice and good, or is a question in which men are concerned who are just and good, either by nature or habit, he who would be a skilful rhetorician has; no need of truth-for that in courts of law men literally care nothing about truth, but only about conviction: and this is based on probability, to which who would be a skilful orator should therefore give his whole attention. And they say also that there are cases in which the actual facts, if they are improbable, ought to be withheld, and only the probabilities should be told either in accusation or defence, and that always in speaking, the orator should keep probability in view, and say good-bye to the truth. And the observance, of this principle throughout a speech furnishes the whole art.

Phaedr. That is what the professors of rhetoric do actually say, Socrates. I have not forgotten that we have quite briefly touched upon this matter already; with them the point is all-important.

Soc. I dare say that you are familiar with Tisias. Does he not define probability to be that which the many think?

Phaedr. Certainly, he does.

Soc. I believe that he has a clever and ingenious case of this sort: He supposes a feeble and valiant man to have assaulted a strong and cowardly one, and to have robbed him of his coat or of something or other; he is brought into court, and then Tisias says that both parties should tell lies: the coward should say that he was assaulted by more men than one; the other should prove that they were alone, and should argue thus: "How could a weak man like me have assaulted a strong man like him?" The complainant will not like to confess his own cowardice, and will therefore invent some other lie which his adversary will thus gain an opportunity of refuting. And there are other devices of the same kind which have a place in the system. Am I not right, Phaedrus?

Phaedr. Certainly.

Soc. Bless me, what a wonderfully mysterious art is this which Tisias or some other gentleman, in whatever name or country he rejoices, has discovered. Shall we say a word to him or not?

Phaedr. What shall we say to him?

Soc. Let us tell him that, before he appeared, you and I were saying that the probability of which he speaks was engendered in the minds of the many by the likeness of the truth, and we had just been affirming that he who knew the truth would always know best how to discover the resemblances of the truth. If he has anything else to say about the art of speaking we should like to hear him; but if not, we are satisfied with our own view, that unless a man estimates the various characters of his hearers and is able to divide all things into classes and to comprehend them under single ideas he will never be a skillful rhetorician even within the limits of human power. And this skill he will not attain without a great deal of trouble, which a good man ought to undergo, not for the sake of speaking and acting before men, but in order that he may be able to say what is acceptable to God and always to act acceptably to Him as far as in him lies; for there is a saying of wiser men than ourselves, that a man of sense should not try to please his fellow-servants (at least this should not be his first object) but his good and noble masters; and therefore if the way is long and circuitous, marvel not at this, for, where the end is great, there we may take the longer road, but not for lesser ends such as yours. Truly, the argument may say, Tisias, that if you do not mind going so far, rhetoric has a fair beginning here.

Phaedr. I think, Socrates, that this is admirable, if only practicable.

Soc. But even to fail in an honourable object is honourable.

http://classics.mit.edu/Plato/phaedrus.html