Summa contra Gentiles3.110 Chapter CX. Solution of the aforesaid arguments

Consequently it is not difficult to solve the objections that have been raised.

For we are not forced to say that there was error in the intellect of the separate substance by judging a good not to be good; but through not considering the higher good to which his own good should have been referred. His will through being intent on his own good could be the cause of this lack of consideration: for it is free to the will to turn to this or that.

It is also clear that he desired but one good, and that was his own good: but his sin consisted in his disregarding the higher good, to which his own should have been directed. For just as in us there is sin through our desiring inferior goods, those namely of the body, outside the order of reason, so in the devil was there sin through his not referring his own good to the divine.

It is also clear that he strayed from the mean of virtue, inasmuch as he did not submit to the order of his superior, and so to himself gave more than his due, and to God less than was due to Him, as the sovereign rule to whose order all things should be subject. Consequently it is evident that in this sin the mean was not missed through excess of passion, but merely through inequality of justice which is about operations. For in separate substances there can be operations, but passions not at all.

Nor does it follow, that because in the higher bodies there can be no defects, there can be no sin in separate substances. Because bodies and all irrational beings are acted upon, and do not put themselves in action, for they have no dominion over their actions. Wherefore they cannot escape the first rule that puts them in action and moves them; unless they be unable to receive adequately the rectitude of the supreme rule, owing to an indisposition of matter. Wherefore the higher bodies in which there cannot be any indisposition of matter, can never depart from the rectitude of the first rule. But rational or intellectual substances are not only acted upon, but they also move themselves to their own actions. And this applies to them all the more, according as their nature is the more perfect: since the more perfect a thing’s nature, the more perfect is its power for action. Consequently the perfection of their nature does not prevent the possibility of sin in them in the manner explained above; namely, through adhering to themselves, and disregarding the order of the superior agent.