Whether the demons' intellect is darkened by privation of the knowledge of all truth?

❌ Objection 1 : It would seem that the demons' intellect is darkened by being deprived of the knowledge of all truth. For it they knew any truth at all, they would most of all know themselves; which is to know separated substances. But this is not in keeping with their unhappiness: for this seems to belong to great happiness, insomuch as that some writers have assigned as man's last happiness the knowledge of the separated substances. Therefore the demons are deprived of all knowledge of truth.

❌ Objection 2 : Further, what is most manifest in its nature, seems to be specially manifest to the angels, whether good or bad. That the same is not manifest with regard to ourselves, comes from the weakness of our intellect which draws its knowledge from phantasms; as it comes from the weakness of its eye that the owl cannot behold the light of the sun. But the demons cannot know God, Who is most manifest of Himself, because He is the sovereign truth; and this is because they are not clean of heart, whereby alone can God be seen. Therefore neither can they know other things.

❌ Objection 3 : Further, according to Augustine (Gen. ad lit. iv, 22), the proper knowledge of the angels is twofold; namely, morning and evening. But the demons have no morning knowledge, because they do not see things in the Word; nor have they the evening knowledge, because this evening knowledge refers the things known to the Creator's praise (hence, after "evening" comes "morning" [Gn. 1]). Therefore the demons can have no knowledge of things.

❌ Objection 4 : Further, the angels at their creation knew the mystery of the kingdom of God, as Augustine says (Gen. ad lit. v, 19; De Civ. Dei xi). But the demons are deprived of such knowledge: "for if they had known it, they would never have crucified the Lord of glory," as is said 1 Cor. 2:8. Therefore, for the same reason, they are deprived of all other knowledge of truth.

❌ Objection 5 : Further, whatever truth anyone knows is known either naturally, as we know first principles; or by deriving it from someone else, as we know by learning; or by long experience, as the things we learn by discovery. Now, the demons cannot know the truth by their own nature, because, as Augustine says (De Civ. Dei xi, 33), the good angels are separated from them as light is from darkness; and every manifestation is made through light, as is said Eph. 5:13. In like manner they cannot learn by revelation, nor by learning from the good angels: because "there is no fellowship of light with darkness [*Vulg.: 'What fellowship hath . . . ?']" (2 Cor. 6:14). Nor can they learn by long experience: because experience comes of the senses. Consequently there is no knowledge of truth in them.