Vitae philosophorum

Diogenes Laertius

Diogenes Laertius. Hicks, R. D., editor. Cambridge, MA.: Harvard University Press; London: William Heinemann Ltd., 1925.

Of these the former is a proposition, the latter a conception. Now where he has a firm grasp Plato expounds his own view and refutes the false one, but, if the subject is obscure, he suspends judgement. His own views are expounded by four persons, Socrates, Timaeus, the Athenian Stranger,[*](In the Laws.) the Eleatic Stranger.[*](In the Sophist and the Statesman.) These strangers are not, as some hold, Plato and Parmenides, but imaginary characters without names,[*](That the Eleatic Stranger is not Parmenides is decisively proved by Soph. 241 e.) for, even when Socrates and Timaeus are the speakers, it is Plato’s doctrines that are laid down. To illustrate the refutation of false opinions, he introduces Thrasymachus, Callicles, Polus, Gorgias, Protagoras, or again Hippias, Euthydemus and the like.

In constructing his proofs he makes most use of induction, not always in the same way, but under two forms. For induction is an argument which by means of certain true premisses properly infers a truth resembling them. And there are two kinds of induction, the one proceeding by way of contradiction, the other from agreement. In the kind which proceeds by contradiction the answer given to every question will necessarily be the contrary of the

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respondent’s position, e.g. My father is either other than or the same as your father. If then your father is other than my father, by being other than a father he will not be a father. But if he is the same as my father, then by being the same as my father he will be my father.

And again: If man is not an animal, he will be either a stick or a stone. But he is not a stick or a stone; for he is animate and self-moved. Therefore he is an animal. But if he is an animal, and if a dog or an ox is also an animal, then man by being an animal will be a dog and an ox as well. This is the kind of induction which proceeds by contradiction and dispute, and Plato used it, not for laying down positive doctrines but for refutation. The other kind of induction by agreement appears in two forms, the one proving the particular conclusion under discussion from a particular, the other proceeding by way of the universal [by means of particular facts]. The former is suited to rhetoric, the latter to dialectic. For instance, under the first form the question is raised, Did so-and-so commit a murder? The proof is that he was found at the time with stains of blood on him.

This is the rhetorical form of induction, since rhetoric also is concerned with particular facts and not with universals. It does not inquire about justice in the abstract, but about particular cases of justice. The other kind, where the general proposition is first established by means of particular facts, is the induction of dialectic. For instance, the question put is whether the soul is immortal, and whether the living come back from the dead. And this is proved in the dialogue On the Soul by means of a certain general proposition, that opposites proceed

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from opposites. And the general proposition itself is established by means of certain propositions which are particular, as that sleep comes from waking and vice versa, the greater from the less and vice versa. This is the form which he used to establish his own views.

But, just as long ago in tragedy the chorus was the only actor, and afterwards, in order to give the chorus breathing space, Thespis devised a single actor, Aeschylus a second, Sophocles a third, and thus tragedy was completed, so too with philosophy: in early times it discoursed on one subject only, namely physics, then Socrates added the second subject, ethics, and Plato the third, dialectics, and so brought philosophy to perfection. Thrasylus says that he published his dialogues in tetralogies, like those of the tragic poets. Thus they contended with four plays at the Dionysia, the Lenaea, the Panathenaea and the festival of Chytri.[*](Pots.) Of the four plays the last was a satiric drama; and the four together were called a tetralogy.