Aristotle Rhetoric 3.11.13

[13] But they are excellent when there is a proportional metaphor; for it is possible to liken a shield to the goblet of Ares and a ruin to the rag of a house; to say that Niceratus is a Philoctetes bitten by Pratys, to use the simile of Thrasymachus, when he saw Niceratus, defeated by Pratys in a rhapsodic competition, still dirty with his hair uncut. ¹ It is herein that poets are especially condemned if they fail, but applauded if they succeed. I mean, for instance, when they introduce an answering clause: ² or again, All such expressions are similes, and similes, as has been often said, are metaphors of a kind.