Aristotle, Rhetoric
J. H. Freese, Ed.

as the universal to the particular. [16] As to signs, some are related as the particular to the universal, others as the universal to the particular. Necessary signs are called tekmeria; those which are not necessary have no distinguishing name. [17] I call those necessary signs from which a logical syllogism can be constructed, wherefore such a sign is called tekmērion; for when people think that their arguments are irrefutable, they think that they are bringing forward a tekmērion, something as it were proved and concluded; for in the old language tekmar and peras have the same meaning （limit, conclusion）.

[18] Among signs, some are related as the particular to the universal; for instance, if one were to say that all wise men are just, because Socrates was both wise and just. Now this is a sign, but even though the particular statement is true, it can be refuted, because it cannot be reduced to syllogistic form. But if one were to say that it is a sign that a man is ill, because he has a fever, or that a woman has had a child because she has milk, this is a necessary sign. This alone among signs is a tekmērion; for only in this case, if the fact is true, is the argument irrefutable. Other signs are related as the universal to the particular, for instance, if one were to say that it is a sign that this man has a fever, because he breathes hard; but even if the fact be true,
this argument also can be refuted, for it is possible for a man to breathe hard without having a fever. We have now explained the meaning of probable, sign, and necessary sign, and the difference between them; in the Analytics¹ we have defined them more clearly and stated why some of them can be converted into logical syllogisms, while others cannot.

[19] We have said that example is a kind of induction and with what kind of material it deals by way of induction. It is neither the relation of part to whole, nor of whole to part, nor of one whole to another whole, but of part to part, of like to like, when both come under the same genus, but one of them is better known than the other. For example, to prove that Dionysius is aiming at a tyranny, because he asks for a bodyguard, one might say that Pisistratus before him and Theagenes of Megara did the same, and when they obtained what they asked for made themselves tyrants. All the other tyrants known may serve as an example of Dionysius, whose reason, however, for asking for a bodyguard we do not yet know. All these examples are contained under the same universal proposition, that one who is aiming at a tyranny asks for a bodyguard.