The Metaphysics of Aristotle

...which proceeds through opposite arguments, and also of that which is alone conversant with the confutation of the false. Hence, Socrates exercises young men like a god, confirming (as in the Theaetetus) whether that which appears to every one is true or not, and whether science is sense or not. In the Lysis, also, where he investigates what a friend is, at one time he evinces that the similar is a friend to the similar, and at another time, that the contrary is a friend to the contrary. And, at one time, that the lover is a friend, and at another the beloved. An exercise of this kind, therefore, is adapted to young men who are lovers of learning, and who possess a manly strength of mind, that they may not be wearied in their investigations. But, when he contends with the Sophists, who pretend to be skilled in all sciences and arts, he employs the elenctic elenctic: Relating to the Socratic method of refutation by cross-examination. modes of dialectic, evincing, that in their assertions they contradict themselves, till, being vanquished on all sides by this artifice, (original: "παρακρουομενοι" — translated: being led into error/thwarted), they are made sensible of their own false wisdom, and become purified from erroneous opinion. The Gorgias, too, and Protagoras are full of this kind of dialectic, and such other dialogues as are intended as a defence against the attacks of the Sophists, such as the contests in the Republic with Thrasymachus. But when the persons of the dialogue neither require reproof, nor exercise, he extends the first energy, and genuinely unfolds the truth of dialectic; as when Socrates in the Phaedo, establishing certain hypotheses, and investigating things consequent to these, shows that the soul is not the recipient of that which is contrary to itself, viz. death; and, having demonstrated this to those who are present, he again refers them to the first hypotheses, and desires them to consider whether they are true.

The dialectic energy therefore is triple, either subsisting through opposite arguments, or alone unfolding truth, or alone confuting falsehood: