Thomas Aquinas

“ The demons are allured by means of creatures, which were made, not by them, but by God. They are enticed by various objects differing according to the various things in which they delight, not as animals by meat, but as spirits by signs, such as are to each one's liking, by means of various kinds of stones, herbs, trees, animals, songs and rites. ”

“ Some wear round their necks a passage in writing from the Gospel. Yet is not the Gospel read in church and heard by all every day? How then, if it does a man no good to have the Gospels in his ears, will he find salvation by wearing them round his neck? ”

“ In blending together medicinal herbs, it is not lawful to make use of observances or incantations, other than the divine symbol, or the Lord's Prayer, so as to give honor to none but God the Creator of all. ”

“ It belongs to the domain of the divine majesty, to Whom the demons are subject, that God should employ them to whatever purpose He will. But man has not been entrusted with power over the demons, to employ them to whatsoever purpose he will; on the contrary, it is appointed that he should wage war against the demons. ”

“ Further, it is unreasonable to deny that which nearly everybody experiences. Now nearly everyone experiences that certain times, or places, hearing of certain words meetings of men or animals, uncanny or ungainly actions, are presages of good or evil to come. ”

“ Dei x, 11) , that "by herbs, stones, animals, certain particular sounds, words, shapes and devices, or again by certain movements of the stars observed in the course of the heavens it is possible for men to fashion on earth forces capable of carrying into effect the various dispositions of the stars," as though the results of the magic arts were to be ascribed to the power of the heavenly bodies. In fact as Augustine adds (De Civ. Dei x, 11) , "all these things are to be ascribed to the demons, who delude the souls that are subject to them." ”

“ Even in the case of incantations of serpents or any animals whatever, if the mind attend exclusively to the sacred words and to the divine power, it will not be unlawful. Such like incantations, however, often include unlawful observances, and rely on the demons for their result, especially in the case of serpents, because the serpent was the first instrument employed by the devil in order to deceive man. ”

“ Such things seem fearsome to those who do not understand them." Again, one should take care lest it contain anything false, because in that case also the effect could not be ascribed to God, Who does not bear witness to a falsehood. ”

“ To seek knowledge of the future from the demons is a sin not only because they are ignorant of the future, but also on account of the fellowship entered into with them, which also applies to the case in point.
Art. 2 - Whether observances directed to the alteration of bodies, as for the purpose of acquiring health or the like, are unlawful? ”