Plato then explains the opinions which he entertains himself, and refutes false ones; and about doubtful matters he suspends his judgment. His opinions of matters as they appear to him he puts into the mouth of four persons, Socrates, Timæus, an Athenian poet, and an Eleatic stranger. But the strangers are not, as some people have supposed, Plato and Parmenides, but certain nameless imaginary characters. Since Plato asserts as undeniable axioms all the opinions which he puts into the mouth of Socrates or Timæus. But when he is refuting false propositions, he introduces such characters as Thrasymachus, and Callicles, and Polus, and Gorgias, and Protagoras, Hippias too, and Euthydemus, and men of that stamp. But when he is demonstrating anything, then he chiefly uses the inductive form of argument, and that too not of one kind only, but of two. For induction is an argument, which by means of some admitted truths establishes naturally other truths which resemble them. But there are two kinds of induction; the one proceeding from contraries, the other from consequents. — Diogenes Laertius, *Lives of Eminent Philosophers*, Book III, Section XXXIII, trans. C. D. Yonge (1853). **Surface Gloss:** Against skeptics who claim Plato never states positive doctrines, Diogenes explains that Plato speaks his own views through four specific dramatic characters, exposes falsehood through named sophists, and uses two distinct types of induction—one to trap opponents, another to build his own proofs. [Note: Yonge translates *Athenaios xenos* ("Athenian stranger") as "an Athenian poet," misreading or emending *xenos*.] **Separate Your Demolition Voice from Your Architect Voice:** Never use the same rhetorical persona or logical tool to tear down bad ideas and to build your own system. Use sharp binary dilemmas ("from contraries") to expose a rival's incoherence, but switch to cumulative pattern-building ("from consequents") when laying down your own constructive doctrine.
— In our words · Source: Lives of Eminent Philosophers (Diogenes Laertius)