Read the excerpt from The Republic by Plato. Why, I said, that which is healthy causes health, and that which is unhealthy causes disease. Which rhetorical device is used in this excerpt?

The sentence sets opposing ideas against each other: “healthy” causes “health,” while “unhealthy” causes “disease.” This balanced contrast is antithesis, so the correct choice is antithesis. Zeugma links different words to one shared word, synecdoche uses a part to represent a whole, and asyndeton omits conjunctions in a list; none is the main device here.

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