The complete sentence in Aristotle reads Ὕστερον δὲ τὸ παρὰ φύσιν τοῦ κατὰ φύσιν, καὶ ἔκστασίς τίς ἐστιν ἐν τῇ γενέσει τὸ παρὰ φύσιν τοῦ κατὰ φύσιν — literally, "What is contrary to nature is later than what is in accord with nature, and what is contrary to nature is some deviation in its generation from what is in accord with nature." You might prefer J. L. Stocks's less literal translation: "The unnatural is subsequent to the natural, being a derangement of the natural which occurs in the course of its generation" (
The Internet Classics Archive | On the Heavens by Aristotle).
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