[TT] FOURTH, the truth of their turning humans into beasts is explained.

[AG 1] As for how this happens, it is argued on the basis of Chapter “Episcopi” from the Council of Acquira (26, Q. 5) that it is not possible for this to happen: “Whoever believes that a creature can be created or changed for the better or worse or turned into a different variety or appearance except by the Creator Himself Who made everything and through Whom everything was made is without a doubt an infidel and worse than a pagan.” Let us use the arguments of St. Thomas in the Commentary on Pronouncements, Bk. 3, Dist. 8 (“Whether demons can make an impression on the bodily senses by deceiving them through acts of conjuring.” [Sent. 2.8.5.Ag4]), where he first405 argues that they do not. For the form of the animal that is seen ought to exist somewhere, but it cannot exist merely in the sense of perception because a sense holds no image except what it has received from objects. There cannot exist a real beast there on the cited authority of the Canon, nor again can it exist in the object that is seen, for instance when a woman is seen as a beast, because two essential forms cannot exist in the same place at one and the same time. Therefore, since that animal shape that is seen cannot exist anywhere, it cannot be the case that an illusion of conjuring is being made in the eye of the viewer, since vision must necessarily be determined by some shape.

[AG2] Also, if it is said that the shape in question is in the surrounding air, | this cannot be so, because the air is not receptive of some form (image), because the air around that person cannot always remain one and the same on account of its fluid nature, especially when it moves, and also because in that case the transformation would be seen by everyone, which nonetheless does not happen because it seems to be the case that the demons do not deceive the eyes of holy men, at any rate.