Chapter Three of the Third Decade
On the power of demons, concerning which six little questions will be resolved
Question One of Chapter Three of the Third Decade
Whether demons can enter the bodies of human beings and animals
It is asked whether demons can enter the bodies of human beings and of other animals.
To this it first appears that one must respond negatively.
For two created spirits cannot be in one and the same place and coexist exactly in the same space, for they would coexist in the same site, which is contrary to philosophy.
But the soul is in every part of the body, since according to the argument it is whole in the whole and whole in every part. Therefore a demon cannot enter the bodies of animals or of human beings.
Furthermore, if demons could enter the bodies of animals or human beings, they would be united to them in the manner of a vivifying form. But it was proved above that an incorporeal intellectual nature, formally subsisting in itself, cannot be united to a corporeal nature in the manner of a form. Therefore, and so forth.
To this question it is answered that both good and evil angels can enter and move the bodies of animals, and there exercise acts of a rational or irrational soul, because corporeal nature obeys good and evil angels at will with respect to local motion.
For, as Dionysius says in chapter 7 of The Divine Names, divine wisdom has joined the ends of the first things to the beginnings of the second things.
From this it is evident that an inferior nature at its highest point is touched by a superior nature.
Corporeal nature is beneath spiritual nature, and therefore at its highest point it is joined to the superior spiritual nature.
Now, among all corporeal motions, local motion is the higher and more perfect, as is proved in Book VIII of the Physics.
The reason is that through local motion itself a movable thing is not in potency toward anything intrinsic to the thing. Therefore every corporeal nature is naturally apt to be moved and touched immediately by an intellectual nature with respect to local motion, as though moved by it.
Hence the philosophers also held that the highest bodies are moved locally by spiritual substances.
Hence we see that the soul moves the body first and principally by local motion.
And because a good or evil angel operates where it is, it can therefore be within natural bodies and consequently within human bodies, insofar as angels enter into them and move them.
To the first argument it must be said that it is not incongruous for two created spirits to be in the same body if one is there not as in a place but as form in matter, as the soul is in the body, while the other is there as in a place definitively, not circumscriptively, as we shall say concerning good or evil angels which have entered bodies.
To the second argument it is answered that, so far as the present purpose is concerned, a spiritual nature can conceivably enter and be united to a corporeal nature in two ways.
In one way, it can do so in the manner of a form or of a vivifying soul. In this way neither a good angel nor a demon can enter, be united to, or go within natural bodies, whether those of irrational or rational animals.
The reason is, as we have said, that the nature of each angel is a rational substance personally and completely subsisting in itself and consequently is a person, in whose power it does not lie to depersonalize itself. Therefore it cannot be a part of a composite.
In a second way, a created spirit can enter and be united to a natural body, whether irrational or rational, not formally but coexistentially. It does so in such a manner that it exercises in that body all its corporeal powers pertaining to local motion, insofar as it also moves the organs of a rational or irrational animal toward exterior acts similar to the acts of a rational or irrational soul.
And in this way any good or evil angel can do so, as is evident concerning the good angel in the speech of Balaam’s ass in Numbers, chapter 22, and concerning the evil angel in the speech of the serpent to Lady Eve in Genesis, chapter 3, and concerning both in many other places of Sacred Scripture.
These things are from Saint Thomas and Henry of Assia.
Take note that, when the author says that a demon can exercise acts of life, whether of a rational or irrational soul, you should not understand that it can operate directly upon the intellect and will, because only corporeal things obey angels and demons, but indirectly—namely, upon the body which is also informed by the rational soul.