Question Four of Chapter Two of the Third Decade
What operations of life a demon exercises in an assumed body
It is asked whether demons exercise true operations of life in assumed bodies.
To this it is answered that those operations which belong to a living body insofar as it is living—that is, insofar as it is animated by a form which is a part of the composite—do not belong to good or evil angels in bodies assumed by them.
For, as we have said, the bodies assumed by them do not live, since those spirits are not united to such bodies as forms.
Therefore, since seeing, sensing, eating, hearing, generating, and things of this kind belong to a body insofar as it is living, they do not properly belong to angels in bodies assumed by them, except by way of likeness.
Hence they do not see through the eyes; rather, their cognitive power is signified through the eyes.
Nor are they properly said to eat, because eating properly imports the taking of food which can be converted into the substance of the one eating through the digestion of the food descending to the stomach. This does not belong to a body assumed by an angel, since it is not of such a nature that nourishment can be converted into it.
For this reason the angel said to Tobias in Tobias, chapter 12: “When I was with you, I indeed appeared to eat and drink with you, but I use invisible food and drink which cannot be seen by human beings.”
And one must speak in the same way concerning the other operations, the powers of the other senses, and the powers of the bodies assumed by angels.
Nor does generation belong to them in such a way that someone is born from them as though from intercourse and their own seed.
Nevertheless, generation can be completed through the act of an evil angel alone, insofar as demons could become succubi to a man and receive seed, then incubi to a woman, and thus place human seed in a suitable location and complete generation in this way. We read that this was done in the case of the giants before and after the Flood, and Augustine adduces it in Book XV of The City of God, chapter 23.
Nevertheless, children born in this way will not be called children of demons, but of those from whom the seed had been elicited.
And if it is said that angels speak, as is evident in many places of Sacred Scripture, while speech is an operation of a living thing, since it is made through a voice, which is sound brought forth from the mouth of an animal, according to Book II On the Soul, it is answered that angels do not speak through assumed bodies.
Rather, they effect something similar to speech insofar as they form in the air sounds similar to human voices, as is evident in a gnat and a mosquito.
If it is likewise said that they are moved and walk—which are operations of life according to Book II On the Soul, as is evident when they went with the younger Tobias and with Abraham—it is said that they were not moved properly.
For that motion was not joined to the angelic mover as to a form. Rather, they were said to be moved accidentally at the motion of the bodies, just as movers are moved in movable things—for example, a sailor at the motion of the ship.
Those operations, however, which belong to a movable body insofar as it is movable—such as to move, to impel, to divide, and things of this kind—belong to them in themselves, since corporeal nature obeys them at will with respect to corporeal motion, as will be said below.
All these things are from the doctors in Book II of the Sentences and Thomas in the First Part, question 51.