Plutarch De E apud Delphos 6

[6] Nicander having delivered these words, our friend Theon, whom you know, asked Ammonius if he might have liberty to plead for logic, which was so highly injured. And Ammonius bidding him speak and defend it, he said: Now that this God is a most expert logician many of his oracles show; for it is, to wit, the part of the same artist to dissolve and frame ambiguities. Moreover, as Plato said, when an oracle was given to the Greeks that they should double the altar in Delos, which is a work of the utmost perfection in geometry, that the God did not order the doing of that very thing, but commanded the Greeks to apply themselves to geometry; so the same God, by giving ambiguous oracles, honors and recommends logic, as necessary to those who desire to understand him aright. Now this conjunction El, or if, has a very great efficacy in logic, as forming the most rational proposition; for how can it be otherwise, since the very brutes have indeed the knowledge of the substance of things, but to man only has Nature given the consideration and judgment of consequence? For that there is both day and light, wolves and dogs and birds are sensible. But that if it is day there must be light, no other animal understands but man, who only has the conception of antecedent and consequent, of the significance and connection of these things with one another, and of their habitude and difference, from which demonstrations take their principal beginnings. Now since philosophy is conversant about truth, since the light of truth is demonstration, and the beginning of demonstration this connection of propositions; the faculty which contains and effects this was by wise men, with good reason, consecrated to the God who most of all loves truth. Now the God indeed is a prophet, and the art of prophesying is a divination concerning the future from things that are present and past. For neither is the original of any thing without a cause, nor the foreknowledge of any thing without reason. But since all things that are done follow and are connected to those that have been done, and those that shall be done to those that are done, according to the progress proceeding from the beginning to the end; he who knows how to look into the causes of this together, and naturally connect them one with another, knows also and divines And Homer indeed excellently well places first things that are present, and afterwards what is future and past. For by the very nature of the connection the argument is based on that which now is. Thus, if this is, that preceded; and again, if this is, that shall be. For the knowledge of the consequence is, as has been said, an artificial and rational thing; but sense gives the assumption to reason. Whence (though it may seem indecent to say it) I will not be afraid to aver this, that the tripod of truth is reason, which recognizes the dependence of the consequent on the antecedent, and then, assuming the reality of the antecedent, infers the conclusion of the demonstration. If then the Pythian Apollo delights in music, and is pleased with the singing of swans and the harmony of the lute, what wonder is it that, for the sake of logic, he embraces and loves this argumentative particle, which he sees the philosophers so much and so frequently to use? Hercules indeed, not having yet unbound Prometheus, nor conversed with the sophisters that were with Chiron and Atlas, but being still a young man and a plain Boeotian, at first abolished logic and derided this word EI; but afterwards he seemed by force to have seized on the tripod, and contended with our God himself for the pre-eminence in this art; for being grown up in age, he appeared to be the most expert both in divination and logic.