Objection 1: It would seem that the natural law can be abolished from the heart of man. Because on Rom. 2:14, "When the Gentiles who have not the law," etc. a gloss says that "the law of righteousness, which sin had blotted out, is graven on the heart of man when he is restored by grace." But the law of righteousness is the law of nature. Therefore the law of nature can be blotted out.
Obj. 2: Further, the law of grace is more efficacious than the law of nature. But the law of grace is blotted out by sin. Much more therefore can the law of nature be blotted out.
Obj. 3: Further, that which is established by law is made just. But many things are enacted by men, which are contrary to the law of nature. Therefore the law of nature can be abolished from the heart of man.
On the contrary, Augustine says (Confess. ii): "Thy law is written in the hearts of men, which iniquity itself effaces not." But the law which is written in men's hearts is the natural law. Therefore the natural law cannot be blotted out.
I answer that, As stated above (AA. 4, 5), there belong to the natural law, first, certain most general precepts, that are known to all; and secondly, certain secondary and more detailed precepts, which are, as it were, conclusions following closely from first principles. As to those general principles, the natural law, in the abstract, can nowise be blotted out from men's hearts. But it is blotted out in the case of a particular action, in so far as reason is hindered from applying the general principle to a particular point of practice, on account of concupiscence or some other passion, as stated above (Q. 77, A. 2). But as to the other, i.e. the secondary precepts, the natural law can be blotted out from the human heart, either by evil persuasions, just as in speculative matters errors occur in respect of necessary conclusions; or by vicious customs and corrupt habits, as among some men, theft, and even unnatural vices, as the Apostle states (Rom. i), were not esteemed sinful.
Reply Obj. 1: Sin blots out the law of nature in particular cases, not universally, except perchance in regard to the secondary precepts of the natural law, in the way stated above.
Reply Obj. 2: Although grace is more efficacious than nature, yet nature is more essential to man, and therefore more enduring.
Reply Obj. 3: This argument is true of the secondary precepts of the natural law, against which some legislators have framed certain enactments which are unjust.