To Florus 6.19

Someone may say here: What then? Do you deny that the innocence in which he was created was corrupted by committing a voluntary sin? Even if committing injustice does not destroy the possibility of returning to good, it is still certain that the standing of innocence with which human life begins perishes through a fault of will. I do not deny that this is so. But what I want these examples to illuminate is this: the qualities by which we are called good and evil were made to operate under the will’s authority. This was established so firmly that even innocence, which precedes the will’s activity because of the author’s dignity and is natural, has no power to preserve itself in a resisting mind. Therefore this principle must apply far, far more strongly on evil’s side: a fault adopted voluntarily must acquire no tyranny that destroys reason.

If the good quality with which humanity was made was not unchangeable—for someone unable to vary his own movements would falsely be called free—much less could an evil quality become unchangeable in a rational being. Otherwise the principle of freedom would suffer from evil’s side a restriction that, to preserve its condition, it had not suffered even from goodness’s side.