Article 36

In the thirty-sixth article, the question is raised whether the demons can know all the thoughts of the heart—including images in the imagination or certain concomitant passions in the body.

I think this is true in regard to the thoughts that accompany certain bodily motions. Augustine also says this in the work, The Divination of Demons in which he says: with greatest facility the demons attain in-depth knowledge of the intentions of men whether made known vocally or even when, conceived in thought, they are expressed by the body. (See chapter 5 of De Divinatione Demonum, which Thomas also cites in S.Th., I, q. 57, a. 4.) He also makes mention of this statement in the book of Retractions when he qualifies, I made this declaration more emphatically than I should have. It has, in fact, been made known through the experience of more than one that such thoughts come to be known by demons. But whether there are certain sensible signs that are hidden to us and yet given to the demons through the bodies of those who are thinking or whether the demons come to know [the intentions of men] by some other spiritual power is something that is either most difficult for men to know or is altogether unable to be ascertained. (See the Retractions, book 2, ch. 56.) But if they know thoughts by means of a spiritual power, even more so do they know bodily motions from which even men sometimes know interior dispositions. Accordingly, the second statement does not exclude the first, but goes further. Nevertheless, it does not seem to me that forms of knowledge only existing in the imagination are sufficient for the demons to know human thoughts. After all, by virtue of his reason and free will, man is able to use a species preserved in his imaginative power as a basis for a variety of thoughts and he can even refrain from acting upon it in any way at all.