To Florus 5.20

To ask closely and briefly: when the apostle Paul called it the natural use of the female, do you think he indicated both its possibility and its propriety, or only its possibility? In other words, by ‘natural’ did he mean an act that could and should occur, or one that could occur but should not? If you say, ‘One that could occur, although it should not,’ as happens in adultery, then that other shameful act will not be contrary to nature either, since it is performed with natural organs. But if, recoiling in alarm, you reply with the truth—that the apostle called natural an act directed toward offspring, which could and should be performed honorably because naturally, with the bodies of one woman or several as permitted according to the circumstances of the time—you will undoubtedly confess your argument foolish. By ‘natural use,’ blessed Paul indicated not fornication, as you thought, but the honorable and legitimate union of bodies arranged for fertility.

We therefore rightly defend in general what the Manichaean accused in general. You say this pleasurable union of the sexes was instituted by the devil, is the cause of original sin, and necessitates all crimes. You thus accuse nature itself. What could we more consistently have done than, with the Teacher of the Gentiles as witness, defend on the general ground of nature, and assign to God’s work, what you called naturally evil? Thus, to refute you, we proved that what you call diabolical was naturally instituted. This is the proper and learned way to answer: defend in particular what is accused in particular, and vindicate in general what is accused in general. Mani understood this too. You equal him in crime but not in intelligence. That is why he assigns the whole substance of bodies to the devil; you assign not all of it but, as we said in the preceding book, the better part. Truth has therefore triumphed, surrounded by sacred defenses. Proving through the apostle that married people’s activity is natural, and therefore belongs to God as nature’s creator, it has shattered the inventions of you who swear it comes from transgression, not nature (compare Romans 1:27).