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. _______________________
SIXTH ARTICLE [I, Q. 115, Art. 6]
Whether Heavenly Bodies Impose Necessity on Things Subject to Their
Action?
Objection 1: It would seem that heavenly bodies impose necessity on things subject to their action. For given a sufficient cause, the effect follows of necessity. But heavenly bodies are a sufficient cause of their effects. Since, therefore, heavenly bodies, with their movements and dispositions, are necessary beings; it seems that their effects follow of necessity.
Obj. 2: Further, an agent's effect results of necessity in matter, when the power of the agent is such that it can subject the matter to itself entirely. But the entire matter of inferior bodies is subject to the power of heavenly bodies, since this is a higher power than theirs. Therefore the effect of the heavenly bodies is of necessity received in corporeal matter.
Obj. 3: Further, if the effect of the heavenly body does not follow of necessity, this is due to some hindering cause. But any corporeal cause, that might possibly hinder the effect of a heavenly body, must of necessity be reducible to some heavenly principle: since the heavenly bodies are the causes of all that takes place here below. Therefore, since also that heavenly principle is necessary, it follows that the effect of the heavenly body is necessarily hindered. Consequently it would follow that all that takes place here below happens of necessity.
On the contrary, The Philosopher says (De Somn. et Vigil. [*De Divin. per Somn. ii]): "It is not incongruous that many of the signs observed in bodies, of occurrences in the heavens, such as rain and wind, should not be fulfilled." Therefore not all the effects of heavenly bodies take place of necessity.