To Florus 2.59

Let us leave that aside and crush, by reason’s strength, the argument it seems you could offer at this point. You may say that Scripture describes this union by saying that the two become one flesh, and that in this sense the apostle said ‘through one man’ to indicate the joined bodies of those who beget (Romans 5:12). I will answer that this too counts against your impiety. For it does not say, ‘The two human beings will become one human being,’ but, ‘The two will become one flesh’ (Genesis 2:24). The language of union teaches that this pleasure of those coupling, this desire which affects their sensation and stirs their organs—which, as that wise man understood, strives to make one flesh—was instituted by God and implanted in their bodies before sin.