Q: Whether the Demons' Intellect Is Darkened by Privation of the Knowledge of All Truth?

A: On the contrary,
Dionysius says (Div. Nom. iv) that, "certain gifts were bestowed upon the demons which, we say, have not been changed at all, but remain entire and most brilliant." Now, the knowledge of truth stands among those natural gifts. Consequently there is some knowledge of truth in them.

I answer that,
The knowledge of truth is twofold: one which comes of nature, and one which comes of grace. The knowledge which comes of grace is likewise twofold: the first is purely speculative, as when Divine secrets are imparted to an individual; the other is effective, and produces love for God; which knowledge properly belongs to the gift of wisdom.

Of these three kinds of knowledge the first was neither taken away nor lessened in the demons. For it follows from the very nature of the angel, who, according to his nature, is an intellect or mind: since on account of the simplicity of his substance, nothing can be withdrawn from his nature, so as to punish him by subtracting from his natural powers, as a man is punished by being deprived of a hand or a foot or of something else. Therefore Dionysius says (Div. Nom. iv) that the natural gifts remain entire in them. Consequently their natural knowledge was not diminished. The second kind of knowledge, however, which comes of grace, and consists in speculation, has not been utterly taken away from them, but lessened; because, of these Divine secrets only so much is revealed to them as is necessary; and that is done either by means of the angels, or "through some temporal workings of Divine power," as Augustine says (De Civ. Dei ix, 21); but not in the same degree as to the holy angels, to whom many more things are revealed, and more fully, in the Word Himself. But of the third knowledge, as likewise of charity, they are utterly deprived.

Reply Obj. 1: Happiness consists in self-application to something higher. The separated substances are above us in the order of nature; hence man can have happiness of a kind by knowing the separated substances, although his perfect happiness consists in knowing the first substance, namely, God. But it is quite natural for one separate substance to know another; as it is natural for us to know sensible natures. Hence, as man's happiness does not consist in knowing sensible natures; so neither does the angel's happiness consist in knowing separated substances.

Reply Obj. 2: What is most manifest in its nature is hidden from us by its surpassing the bounds of our intellect; and not merely because our intellect draws knowledge from phantasms. Now the Divine substance surpasses the proportion not only of the human intellect, but even of the angelic. Consequently, not even an angel can of his own nature know God's substance. Yet on account of the perfection of his intellect he can of his nature have a higher knowledge of God than man can have. Such knowledge of God remains also in the demons. Although they do not possess the purity which comes with grace, nevertheless they have purity of nature; and this suffices for the knowledge of God which belongs to them from their nature.

Reply Obj. 3: The creature is darkness in comparison with the excellence of the Divine light; and therefore the creature's knowledge in its own nature is called "evening" knowledge. For the evening is akin to darkness, yet it possesses some light: but when the light fails utterly, then it is night. So then the knowledge of things in their own nature, when referred to the praise of the Creator, as it is in the good angels, has something of the Divine light, and can be called evening knowledge; but if it be not referred to God, as is the case with the demons, it is not called evening, but "nocturnal" knowledge. Accordingly we read in Gen. 1:5 that the darkness, which God separated from the light, "He called night."

Reply Obj. 4: All the angels had some knowledge from the very beginning respecting the mystery of God's kingdom, which found its completion in Christ; and most of all from the moment when they were beatified by the vision of the Word, which vision the demons never had. Yet all the angels did not fully and equally apprehend it; hence the demons much less fully understood the mystery of the Incarnation, when Christ was in the world. For, as Augustine observes (De Civ. Dei ix, 21), "It was not manifested to them as it was to the holy angels, who enjoy a participated eternity of the Word; but it was made known by some temporal effects, so as to strike terror into them." For had they fully and certainly known that He was the Son of God and the effect of His passion, they would never have procured the crucifixion of the Lord of glory.

Reply Obj. 5: The demons know a truth in three ways: first of all by the subtlety of their nature; for although they are darkened by privation of the light of grace, yet they are enlightened by the light of their intellectual nature: secondly, by revelation from the holy angels; for while not agreeing with them in conformity of will, they do agree, nevertheless, by their likeness of intellectual nature, according to which they can accept what is manifested by others: thirdly, they know by long experience; not as deriving it from the senses; but when the similitude of their innate intelligible species is completed in individual things, they know some things as present, which they previously did not know would come to pass, as we said when dealing with the knowledge of the angels (Q. 57, A. 3, ad 3).