SUMMA THEOLOGICA. Thomas Aquinas
than another; and the same applies to other species, because differences which divide a "genus" are contrary to one another. Contraries, however, are compared to one another as the perfect to the imperfect, since the "principle of contrariety is habit, and privation thereof," as is written Metaph. x (Did. ix, 4). The same would follow if the aforesaid substances were composed of matter and form. For if the matter of one be distinct from the matter of another, it follows that either the form is the principle of the distinction of matter---that is to say, that the matter is distinct on account of its relation to divers forms; and even then there would result a difference of species and inequality of nature: or else the matter is the principle of the distinction of forms. But one matter cannot be distinct from another, except by a distinction of quantity, which has no place in these incorporeal substances, such as an angel and the soul. So that it is not possible for the angel and the soul to be of the same species. How it is that there can be many souls of one species will be explained later ( Question [76], Article [2], ad 1).
Reply to Objection 1: This argument proceeds from the proximate and natural end. Eternal happiness is the ultimate and supernatural end.
Reply to Objection 2: The ultimate specific difference is the noblest because it is the most determinate, in the same way as actuality is nobler than potentiality. Thus, however, the intellectual faculty is not the noblest, because it is indeterminate and common to many degrees of intellectuality; as the sensible faculty is common to many degrees in the sensible nature. Hence, as all sensible things are not of one species, so neither are all intellectual things of one species.
Reply to Objection 3: The body is not of the essence of the soul; but the soul by the nature of its essence can be united to the body, so that, properly speaking, not the soul alone, but the "composite," is the species. And the very fact that the soul in a certain way requires the body for its operation, proves that the soul is endowed with a grade of intellectuality inferior to that of an angel, who is not united to a body.
OF THE UNION OF BODY AND SOUL (EIGHT ARTICLES)
We now consider the union of the soul with the body; and concerning this there are eight points of inquiry:
(1) Whether the intellectual principle is united to the body as its form?
(2) Whether the intellectual principle is multiplied numerically according to the number of bodies; or is there one intelligence for all men?
(3) Whether in the body the form of which is an intellectual principle, there is some other soul?
(4) Whether in the body there is any other substantial form?
(5) Of the qualities required in the body of which the intellectual principle is the form?
(6) Whether it be united to such a body by means of another body?
(7) Whether by means of an accident?
(8) Whether the soul is wholly in each part of the body?
Whether the intellectual principle is united to the body as its form?
Objection 1: It seems that the intellectual principle is not united to the body as its form. For the Philosopher says (De Anima iii, 4) that the intellect is "separate," and that it is not the act of any body. Therefore it is not united to the body as its form.
Objection 2: Further, every form is determined according to the nature of the matter of which it is the form; otherwise no proportion would be required between matter and form. Therefore if the intellect were united to the body as its form, since every body has a determinate nature, it would follow that the intellect has a determinate nature; and thus, it would not be capable of knowing all things, as is clear from what has been said ( Question [75], Article [2]); which is contrary to the nature of the intellect. Therefore the intellect is not united to the body as its form.
Objection 3: Further, whatever receptive power is an act of a body, receives a form materially and individually; for what is received must be received according to the condition of the receiver. But the form of the thing understood is not received into the intellect materially and individually, but rather immaterially and universally: otherwise the intellect would not be capable of the knowledge of immaterial and universal objects, but only of individuals, like the senses. Therefore the intellect is not united to the body as its form.
Objection 4: Further, power and action have the same subject; for the same subject is what can, and does, act. But the intellectual action is not the action of a body, as appears from above ( Question [75], Article [2]). Therefore neither is the intellectual faculty a power of the body. But virtue or power cannot be more abstract or more simple than the essence from which the faculty or power is derived. Therefore neither is the substance of the intellect the form of a body.
Objection 5: Further, whatever has "per se" existence is not united to the body as its form; because a form is that by which a thing exists: so that the very existence of a form does not belong to the form by itself. But the intellectual principle has "per se" existence and is subsistent, as was said above ( Question [75], Article [2]). Therefore it is not united to the body as its form.
Objection 6: Further, whatever exists in a thing by reason of its nature exists in it always. But to be united to matter belongs to the form by reason of its nature; because form is the act of matter, not by an accidental quality, but by its own essence; otherwise matter and form would not make a thing substantially one, but only accidentally one. Therefore a form cannot be without its own proper matter. But the intellectual principle, since it is incorruptible, as was shown above ( Question [75], Article [6]), remains separate from the body, after the dissolution of the body. Therefore the intellectual principle is not united to the body as its form.
On the contrary, According to the Philosopher, Metaph. viii (Did. vii 2), difference is derived from the form. But the difference which constitutes man is "rational," which is applied to man on account of his intellectual principle. Therefore the intellectual principle is the form of man.
I answer that, We must assert that the intellect which is the principle of intellectual operation is the form of the human body. For that whereby primarily anything acts is a form of the thing to which the act is to be attributed: for instance, that whereby a body is primarily healed is health, and that whereby the soul knows primarily is knowledge; hence health is a form of the body, and knowledge is a form of the soul. The reason is because nothing acts except so far as it is in act; wherefore a thing acts by that whereby it is in act. Now it is clear that the first thing by which the body lives is the soul. And