On Marriage and Concupiscence

A man, however, is much deceived if, while consenting to the lust of his flesh, and then both resolving in his mind to do its desires and setting about it, he supposes that he has still a right to say, “It is not I that do it,” even if he hates and loathes himself for assenting to evil desires. The two things are simultaneous in his case: he hates the thing himself because he knows that it is evil; and yet he does it, because he is bent on doing it. Now if, in addition to all this, he proceeds to do what the Scripture forbids him, when it says, “Neither yield your members as instruments of unrighteousness unto sin,” and completes with a bodily act what he was bent on doing in his mind; and says, “It is not I that do the thing, but sin that dwells in me,” because he feels displeased with himself for resolving on and accomplishing the deed,— he so greatly errs as not to know his own self.

For, whereas he is altogether himself, his mind determining and his body executing his own purpose, he yet supposes that he is himself no longer! [XXIX.] That man, therefore, alone speaks the truth when he says, “It is no more I that do it, but sin that dwells in me,” who only feels the concupiscence, and neither resolves on doing it with the consent of his heart, nor accomplishes it with the ministry of his body.