Sixthly, there are two reasons why devils molest men at certain phases of the Moon. First, that they may bring disrepute on a creature of God, namely, the Moon, as S. Jerome and S. John Chrysostom say. Secondly, because they cannot, as has been said above, operate except through the medium of the natural powers. Therefore they study the aptitudes of bodies for receiving an impression; and because, as Aristotle says, the brain is the most humid of all the parts of the body, therefore it chiefly is subject to the operation of the Moon, which itself has power to incite humours. Moreover, the animal forces are perfected in the brain, and therefore the devils disturb a man’s fancy according to certain phases of the Moon, when the brain is ripe for such influences.
And there are two reasons why the devils are present as counsellors in certain constellations. First, that they may lead men into the error of thinking that there is some divinity in the stars. Secondly, because they think that under the influence of some constellations corporeal matter is more apt for the deeds that they counsel.
And as to what S. Augustine says in De Ciuitate Dei, XXXVI: Devils are attracted by various kinds of stones, herbs, trees, animals, songs, and instruments of music, not as animals are attracted by food, but as spirits by signs, as if these things were exhibited to them as a sign of Divine honour, for which they are themselves eager.
But it is often objected that devils can be hindered by herbs and music from molesting men; as it is alleged in the argument from Saul and the music of the harp. And hence an attempt is made to argue that some men can work witchcraft through certain herbs and occult causes, without the help of devils, buy only of the influence of the stars, which have more direct power over matter corporeal for corporeal effects than over the devils for effects of witchcraft.
Now, though this must be answered more widely, it is to be noted that herbs and music cannot by their own natural virtue entirely shut out the molestation which the devil can inflict upon men, with the permission of God and the Angels. Yet they can mitigate that molestation; and this can even be of so slight a nature that they can entirely remove it. But they would do this, not by acting against the devil himself, since he is a separate spirit against whom nothing corporeal can naturally act, but by acting against the actual molestation of the devil. For every cause that has limited power can produce a more intense effect on a suitable than upon an unsuitable material. See Aristotle De Anima. They who act do so upon a predisposed patient. Now the devil is an agent of limited power; therefore he can inflict a fiercer affliction on a man disposed to that affliction or to that which the devil means to inflict, than upon a man of a contrary disposition. For example, the devil can induce a fiercer passion of melancholy in a man disposed to that humour than in a man of the contrary disposition.
Moreover, it is certain that herbs and music can change the disposition of the body, and consequently of the emotions. This is evident in the case of herbs, since some incline a man to joy, some to sadness, and so with others. It is evident also in the case of music, as Aristotle shows (Politics, VIII), where he says that different harmonies can produce different passions in a man. Boethius also mentions this in his Music, and the author of the Birth of Knowledge, where he speaks of the usefulness of music, and says that it is of value in the cure or alleviation of various infirmities. And thus, other things being equal, it may help to weaken the affliction.
But I do not see how herbs or music can cause a man to be of such a disposition that he can in no way be molested by the devil. Even if such a thing were permissible, the devil, moving only in local vapour of the spirit, can grievously affect men supernaturally. But herbs and harmonies cannot of their own natural virtue cause in man a disposition by which the devil is prevented from creating the aforesaid commotion. Nevertheless it sometimes happens that the devil is permitted to inflict only so small a vexation on a man that, through some strong contrary disposition, it may be totally removed; and then some herbs or harmonies can so dispose a man’s body to the contrary that the vexation is totally removed. For example, the devil may at times vex a man with the affliction of sadness; but so weakly that herbs or harmonies which are capable of causing a swelling and uplifting of the spirits, which are contrary emotions to sadness, can totally remove that sadness.
Moreover, S. Augustine, in his Second Book On the Christian Doctrine, condemns amulets and certain other things of which he there writes much, attributing their virtue to magic art, since thy can have no natural virtue of their own. And this is clear from what he says. To this sort belong all amulets and charms which are condemned by the School of Physicians, which condemns very clearly their use, in that they have no efficacy of their own natural virtue.
And as for that concerning 1 Kings 16: that Saul, who was vexed by a devil, was alleviated when David played his harp before him, and that the devil departed, etc. It must be known that it is quite true that by
