I used “witches” instead of “magicians” in the title, because, to us, a magician is a card sharp, but some still know of the supernatural feats of witches. We might also use psychics.
1 There have been some who say that works of this kind, which are astonishing to us when accomplished by the arts of magic, are not performed by spiritual substances but by the power of celestial bodies. An indication of this is seen in the fact that the precise position of the stars is carefully noted by those who perform these works. Moreover, they make use of certain herbs, and other corporeal things, as aids in the preparation, as it were, of low-grade matter for the reception of the influence of celestial power.
2 But this view is clearly opposed by the apparitions. Indeed, since it is not possible for understanding to be caused by corporeal principles, as we proved above, it is impossible for effects peculiar to intellectual nature to be caused by the power of a celestial body.
Now, among these workings of the magicians some events appear which are the proper functions of a rational nature. For instance, answers are given concerning things removed by theft, and concerning other such matters, and this could be done only through understanding. So, it is not true that all effects of this kind are caused solely by the power of celestial bodies.
Notes This is where psychics—and not mental magicians—enter. It’s very easy to fake real magic by use of techniques like “cold reading”. We are thinking here of real and not faked cases.
3 Again, speech is itself an act peculiar to a rational nature. Now, certain agents that speak to men appear in these performances, and they reason discursively about various matters. Therefore, it is not possible for things like this to be done solely by the power of celestial bodies.
4 Now, if someone says that apparitions of this kind do not work through external sensation, but only through the imagination, then, first of all, this does not seem true. In fact, imaginary forms do not look like true things to an observer unless there be a loss of discriminatory power in the external senses. For it is impossible for a person to be made to regard images as things unless the natural power of sense discrimination has been overcome. But these vocal messages and apparitions are made to men who exercise their external senses freely. So, it is not possible for these visions and auditory responses to be solely a matter of imagination.
5 Then, too, from imaginary forms it is not possible for intellectual knowledge beyond the natural or acquired ability of the intellect to come to a person. This is clear even in the case of dreams, in which, though there may be some premonition of future events, not everyone who experiences dreams is able to understand their meaning.
But, through these visions or auditory messages which appear in the performances of magicians, intellectual knowledge of things which surpass the capacity of his understanding often comes to a person. Examples are the revealing of hidden treasures, the showing of future events, and sometimes true answers are given concerning scientific demonstrations. So, it must be that either these apparitions and vocal messages are not grasped through the imagination only, or, at least, that this case of a man being brought to a knowledge of such matters through imaginary presentations of this kind is done by the power of a higher understanding, and is not done solely by the power of celestial bodies.
Notes Do not dismiss all your dreams.
6 Again, what is done by the power of celestial bodies is a natural effect, for the forms that are caused in lower bodies by the power of celestial bodies are natural. So, that which cannot be natural for anything cannot be done by the power of celestial bodies. But some such things are said to be done during the aforementioned performances; for instance, in the presence of a certain man, the bolt of any door is opened for him, a certain person can become invisible, and many other such things are reported. Therefore, it is not possible for this to be done by the power of celestial bodies.
7 Besides, whenever a subsequent perfection is conferred on a subject by the power of the celestial bodies, what is prior to this perfection is also conferred. Now, the power of self-movement is subsequent to the possession of a soul, for it is proper to animated beings for them to move themselves. So, it is impossible for something inanimate to be made able to move itself by the power of celestial bodies. But it is said that this can be done by the arts of magic; that a statue, for instance, can move itself, or even speak. So, it is not possible for the effect of the arts of magic to be done by celestial power.
8 Now, if it is suggested that this statue receives a principle of life from the power of celestial bodies, this is impossible. In fact, the principle of life in all living things is the substantial form, “for living beings, to live is to be,” as the Philosopher says in Book II  of On the Soul. But it is impossible for a thing to receive a new substantial form without losing the form which it previously possessed, “for the generation of one thing is the corruption of another thing.” Now, in the process of making a statue no substantial form is ejected; rather, what is accomplished is a change of shape only, and this is accidental; the form of copper, or other material, remains. So, it is not possible for these statues to receive a principle of life.
Notes Again, we’re not talking fakery here. That kind of “magic” was mostly unknown during Aquinas’s day.
9 Again, if anything is moved by a principle of life, it must have sense power: the mover is, in fact, sense or understanding. Now, understanding is not present in things subject to generation and corruption, without sensation. But sensation cannot be present where there is no touch, nor can touch be without an organ that has a balanced mixture of sensory qualities. Now, such a balanced mixture is not found in stone, or wax, or metal, from which a statue is made. Therefore, it is not possible for these statues to be moved by a principle of life.
10 Besides, perfect living things are not generated by the celestial power alone, but also from semen, “for man, together with the sun, generates a man.” On the other hand, things generated without semen, by the celestial power alone, are animals generated from putrefaction, and they are the lower type of animals. So, if these statues receive a principle of life, whereby to move themselves, through the celestial power alone, they must be the lowest grade of animals. Yet this would be false if they work through an internal principle of life, for noble operations appear among their activities, since they give answers about hidden things.
11 Moreover, it is possible for a natural effect produced by the power of celestial bodies to be accomplished without the operation of an art. For, though a man might work by means of some artful device for the purpose of generating frogs, yet it happens that frogs are generated without any artificial device. So, if these statues that are made by the art of necromancy receive their principle of life from the power of celestial bodies, there should be a possibility of finding a case of the generation of such statues apart from art of this kind. But such a case is not found. It is obvious, then, that these statues do not have a principle of life, nor are they moved by the power of a celestial body.
Notes And here we have genetics!
12 The position of Hermes is disposed of by these considerations, for he spoke as follows, as Augustine reports it in the City of God [VIII, 23]: “Just as God is the maker of the celestial gods, so man is the maker of the gods who are in the temples, content in their nearness to man. I mean the animated statues, endowed with sense and spirit, that do such great and unusual things; statues that foresee future events, predicting them from dreams and from many other things, that cause weaknesses in men and also cure them, that give sorrow and joy, in accord with one’s merits.”
13 This view is also refuted by divine authority, for it is said in the Psalm (134:15-17): “The idols of the Gentiles are silver and gold, the works of men’s hands. They have a mouth and they do not speak… neither is there any breath in their mouths.”
14 However, it does not seem necessary to deny altogether that some power may be present in the aforementioned objects, resulting from the power of the celestial bodies—only it will be for those effects, of course, which any lower bodies are able to produce by the power of celestial bodies.