Summa contra Gentiles2.92 Chapter XCII. Of the great number of separate substances

It must here be noted that Aristotle attempts to prove that not only some intellectual substances exist apart from a body, but also that they are of the same number, neither more nor less, as the movements observed in the heaven.

Thus, he proves that in the heaven there are no movements that cannot be observed by us, from the fact that every movement in the heaven is on account of the movement of some star, which is perceptible to the senses: since the spheres carry the stars and the movement of the carrier is on account of the movement of the carried. Again he proves that there are no separate substances from which some movement does not result in the heaven: because, since the heavenly movements are directed to the separate substances as their respective ends; if there were any separate substances besides those which he enumerates, there would be certain movements directed to them as an end: otherwise such movements would be imperfect. Wherefore he concludes from these premisses that separate substances are not more numerous than the movements that are and can be observed in the heaven: and all the more since there are not several heavenly bodies within the same species, so that there might also be several movements unknown to us.

But this argument is not cogent. For in things directed to an end, necessity depends on the end, as he himself teaches (2 Phys.), and not vice versa. Wherefore if as he states the heavenly movements are directed to separate substances as their respective ends; we cannot necessarily conclude the number of the aforesaid substances from the number of the movements. For it might be said that there are some separate substances of a higher nature than those which are the proximate ends of the heavenly movements; even as, if tools be on account of the men who work by means of them, this does not hinder there being other men who do not work immediately with those tools, but direct the workers. Hence Aristotle himself adduces this argument, not as cogent but as probable: for he says Wherefore it is reasonable to reckon stick to be the number of unchangeable substances and principles: for we may leave it to more capable persons to decide the point with certainty.

It remains, then, to be shown that the intellectual substances that are separate from bodies are far more numerous than the heavenly movements. For intellectual substances transcend, in their genus, all corporeal nature. Wherefore we must mark the degrees of the aforesaid substances according to their transcendency above corporeal nature. Now some intellectual substances are raised above corporeal substance in their generic nature alone, and are nevertheless united to bodies as forms, as shown above. And since the being of intellectual substances, as regards its genus, is nowise dependent on a body, as we have proved, we find a higher grade of the aforesaid substances, which, though not united to bodies as forms, are nevertheless the proper movers of certain definite bodies. In like manner the nature of an intellectual substance does not depend on its causing movement, since to move is consequent upon their principal operation which is to understand. Hence there will be a yet higher grade of intellectual substances, which are not the proper movers of certain bodies, but are raised above movers.

Moreover. Even as that which acts by its nature, acts by its natural form, so that which acts by its intelligence acts by its intellectual form, as instanced in those who act by their art. Accordingly, as the natural agent is proportionate to the patient by reason of its natural form, so the intelligent agent is proportionate to the patient and to the thing made, through the form of its intellect; so that, in effect, the intellective form is such that it can be induced by the agent’s action into the matter which receives it. Hence the proper movers of the spheres,—since they move by their intellect (if we wish to uphold the opinion of Aristotle on this point)—must needs have such intelligences as are in harmony with the movements of the spheres, and reproducible in natural things. But above these intelligible concepts we can apprehend some that are yet more universal: because the intellect apprehends the forms of things in a manner that is more universal than is their being in things: for which reason we find that the form of the speculative intellect is more universal than that of the practical intellect, and among the practical arts, the concept of the commanding art is more universal than that of the executive art. Now we must assign degrees to intellectual substances according to the degree of intellectual operation proper to them. Therefore there are some intellectual substances above those which are the proper and proximate movers of certain definite spheres.

Again. Seemingly the order of the universe requires that whatever is more noble among things should exceed in quantity or number the less noble: since the less noble would seem to be for the sake of the more noble. Hence the more noble things, as existing for their own sake, should be as numerous as possible. Hence we find that incorruptible, i.e. the heavenly, bodies so far surpass corruptible, i.e. the elemental, bodies, that the latter are inconsiderable in quantity as compared with the former. Now just as the heavenly bodies, being incorruptible, are more noble than the elements which are corruptible, so intellectual substances are more noble than all bodies, even as the immovable and the immaterial is more noble than the movable and material. Therefore separate intellectual substances surpass in number the whole multitude of material things: and consequently they are not confined to the number of heavenly movements.

Again. The species of material things are multiplied not through their matter but through their form. Now, forms existing apart from matter, have a more complete and universal being than forms existing in matter: because forms are received into matter according to the receptivity of matter. Wherefore seemingly forms existing apart from matter, which we call separate substances, are not less in number than the species of material things.

Yet we do not therefore say that separate substances are the species of these sensible things, as the Platonists maintained. For since they could not attain to the knowledge of the aforesaid substances except from sensibles, they supposed those substances to be of the same species as these, or rather to be the species of these latter: even as a person who had not seen the sun, moon, and stars, and heard that they were incorruptible bodies, might call them by the names of these corruptible bodies, thinking them to be of the same species as these: which would not be possible. In like manner it is impossible that immaterial substances be of the same species as material, or that they be the species of the latter substances: because the specific nature of these sensible things requires matter, though not this matter, which is the proper principle of the individual: even as the specific nature of man requires flesh and bones, but not this flesh and these bones, which are the principles of Socrates and Plato. Accordingly we do not say that separate substances are the species of these sensibles, but that they are other species more noble than these, forasmuch as the pure is raised above the mixture. And thus those substances must needs be more numerous than the species of these material things.

Further. The possibility of multiplication applies to a thing in its intelligible being rather than in its material being. For we grasp, with our intellect, many things which cannot have being in matter; the result being that any straight line can be produced mathematically, but not in nature; while it is possible for the rarefaction of bodies, the velocity of movements, the diversity of shapes to be multiplied indefinitely in thought, although it is impossible in fact. Now, separate substances have intelligible being by their nature: and consequently a greater multiplicity is possible in them than in material substances, taking into account their respective properties and natures. Now in things everlasting there is no distinction between actual and possible beingTherefore the multitude of separate substances surpasses that of material bodies.

Holy Writ bears witness to this. For it is stated (Dan. vii. id): Thousands of thousands ministered to Him, and ten thousand times a hundred thousand stood before Him. And Dionysius {Coel. Hier. xiv.) says that the number of those substances surpasses all material multitude.

Hereby we set aside the error of those who said that the number of the separate substances corresponds to the number of heavenly movements, or of the heavenly spheres: as well as the error of Rabbi Moses, who said that the number ascribed by Scripture to the angels is not the number of separate substances, but of forces in this lower world; as if one were to give to the concupiscible power the name of spirit of concupiscence, and so on.