Q: Whether Heavenly Bodies Can Act on the Demons?

A: On the contrary,
The demons are superior in the order of nature, to the heavenly bodies. But the "agent is superior to the patient," as Augustine says (Gen. ad lit. xii, 16). Therefore the demons are not subject to the action of heavenly bodies.

I answer that,
There have been three opinions about the demons. In the first place the Peripatetics denied the existence of demons; and held that what is ascribed to the demons, according to the necromantic art, is effected by the power of the heavenly bodies. This is what Augustine (De Civ. Dei x, 11) relates as having been held by Porphyry, namely, that "on earth men fabricate certain powers useful in producing certain effects of the stars." But this opinion is manifestly false. For we know by experience that many things are done by demons, for which the power of heavenly bodies would in no way suffice: for instance, that a man in a state of delirium should speak an unknown tongue, recite poetry and authors of whom he has no previous knowledge; that necromancers make statues to speak and move, and other like things.

For this reason the Platonists were led to hold that demons are "animals with an aerial body and a passive soul," as Apuleius says, quoted by Augustine (De Civ. Dei viii, 16). And this is the second of the opinions mentioned above: according to which it could be said that demons are subject to heavenly bodies in the same way as we have said man is subject thereto (A. 4). But this opinion is proved to be false from what we have said above (Q. 51, A. 1): for we hold that demons are spiritual substances not united to bodies. Hence it is clear that they are subject to the action of heavenly bodies neither essentially nor accidentally, neither directly nor indirectly.

Reply Obj. 1: That demons harass men, according to certain phases of the moon, happens in two ways. Firstly, they do so in order to "defame God's creature," namely, the moon; as Jerome (In Matt. iv, 24) and Chrysostom (Hom. lvii in Matt.) say. Secondly, because as they are unable to effect anything save by means of the natural forces, as stated above (Q. 114, A. 4, ad 2) they take into account the aptitude of bodies for the intended result. Now it is manifest that "the brain is the most moist of all the parts of the body," as Aristotle says [*De Part. Animal. ii, 7: De Sens. et Sensato ii: De Somn. et Vigil. iii]: wherefore it is the most subject to the action of the moon, the property of which is to move what is moist. And it is precisely in the brain that animal forces culminate: wherefore the demons, according to certain phases of the moon, disturb man's imagination, when they observe that the brain is thereto disposed.

Reply Obj. 2: Demons when summoned through certain constellations, come for two reasons. Firstly, in order to lead man into the error of believing that there is some Divine power in the stars. Secondly, because they consider that under certain constellations corporeal matter is better disposed for the result for which they are summoned.

Reply Obj. 3: As Augustine says (De Civ. Dei xxi, 6), the "demons are enticed through various kinds of stones, herbs, trees, animals, songs, rites, not as an animal is enticed by food, but as a spirit by signs"; that is to say, forasmuch as these things are offered to them in token of the honor due to God, of which they are covetous.