Book Three — Providence, Chapter 105 — Summa Contra Gentiles
[1] Now, it remains to investigate where the arts of magic get their efficacy. Indeed, this can easily be thought out if attention is paid to their method of operation.
[2] As a matter of fact, in their performances they use certain significant words in order to produce given effects. But a word, as endowed with meaning, has no force except as derived from some understanding: either from the understanding of the speaker or from the understanding of the one to whom it is spoken. As an example of such dependence on the understanding of the speaker, suppose an intellect is of such great power that a thing can be caused by its act of conception, and that the function of the spoken word is to present, in some way, this conception to the effects that are produced. As an example of dependence on the understanding of the person to whom the speech is directed, take the case of a listener who is induced to do something, through the reception in his intellect of the meaning of the word. Now, it cannot be claimed that these meaningful words spoken by magicians get their efficacy from the understanding of the speaker. Indeed, since power results from essence, a diversity of power manifests a diversity of essential principles. But the intellect of men in general is so disposed that its knowledge is caused by things, instead of it being able to cause things by its act of conception. So, if there be any men who, by their own power, can change things by the words which express their intellectual thought, they will belong to a different species and will be called men in an equivocal sense.
[3] Moreover, the power to do something is not acquired by study, but only the knowledge of what to do. Now, some men acquire through study the ability to produce these magical performances. So, there is no special power in them to produce effects of this kind, but only knowledge.
[4] Now, if someone says that men like this, in distinction from other men, receive the aforesaid power from birth, due to the power of the stars, so that, no matter how much instruction is given to other men, if they do not possess this from birth, they cannot be successful in works of this kind, our first answer must be that the celestial bodies are not able to make an impression on the understanding, as we showed above. Therefore, no intellect can receive from the power of the stars such a power that the expression of its thought through speech is capable of producing something.
[5] But, if it be said that even the imagination produces something when it utters meaningful words, and that the celestial bodies can make an impression on this utterance since this action is performed by means of a bodily organ, this cannot be true in regard to all the effects produced by these arts. It has been shown that not all of these effects can be produced by the power of the stars. Neither, then, can a man receive from the power of the stars this power to produce such effects.
[6] So, we are left with the conclusion that effects of this kind are accomplished by some understanding to which the speech of the person uttering these words is addressed. An indication of this fact is that meaningful words such as the magicians use are called invocations, supplications, adjurations, or even commands, implying that one person is speaking to another.
[7] Again, in the practices of this art they use certain symbols and specially shaped figures. Now, shape is the principle of neither action nor passion; if it were, mathematical bodies would be active and passive. Hence, it is not possible to dispose matter by special figures so that it will be receptive to a natural effect. So, the magicians do not use figures as dispositions. The conclusion remains, then, that they may use them only as signs, for there is no third possibility. Now, we do not use signs except in regard to other intelligent beings. Therefore, the arts of magic get their efficacy from another intelligent being to whom the speech of the magician is addressed.
[8] Now, if someone says that some figures are proper to certain celestial bodies, and so lower bodies are marked by certain figures for the reception of the influences of the celestial bodies, this does not seem a reasonable answer. In fact, a patient is not ordered to the reception of the influence of an agent, unless it be because it is in potency. So, only those things whereby a thing becomes potential, in some way, determine it to receive a special impression. But matter is not disposed by figures so that it is in potency to any form, because figure, according to its rational meaning, abstracts from all sensible matter and form, for it is a mathematical object. Therefore, a body is not determined by figures or symbols for the reception of any influence from a celestial body.
[9] Moreover, certain figures are assigned as proper to celestial bodies, as their effects; for the shapes of lower bodies are caused by the celestial bodies. But the aforesaid arts do not use characters or figures like the effects of celestial bodies. Rather, they are the productions of man, working by means of art. So, the assigning of certain figures as proper to celestial bodies seems to contribute nothing to the discussion.
[10] Furthermore, as we have shown, natural matter is not in any way disposed toward form by figures. So, the bodies on which these figures are put have the same readiness to receive the celestial influence as any other bodies of the same species. Now, the fact that a thing acts on one of a group of things equally disposed, because of something specially assigned to that agent which is to be found on that object and not on another, is not indicative of an agent which acts by natural necessity, but, rather, of one which acts through will. It is clear, then, that arts of this sort which use figures to produce certain effects do not get their efficacy from a natural agent, but from some intellectual substance that acts through understanding.
[11] Indeed, the very name that they give to such figures demonstrates this point, for they call them characters. As a matter of fact, a character is a sign. By this usage we are given to understand that they do not use these figures except as signs addressed to some intellectual nature.
[12] However, since figures are like specific forms for art objects, some person could say that nothing prevents the construction of a figure, which specifies an image, as result of some power due to celestial influence, not as a figure, but as it specifies the artifact which obtains its power from the stars. However, concerning the letters with which something is written on an image, and the other characters, nothing else can be said than that they are signs. Hence, they are directed only to some intellect. This is also shown by the offerings, prostrations, and other similar practices which they use, for they can be nothing but signs of reverence addressed to some intellectual nature.
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