Chapter 28: The Union Of Soul With Body

[636] The rational soul is the substantial form of the human body, gives that body its own nature, for it is the radical principle by which man lives, vegetatively, sensitively, and intellectively. These various vital acts, since they are not accidental to man, but natural, must come from his nature, from the specific principle which animates his body.

What makes man to be man? Is it his soul alone? No, because each man is aware that he uses not only his mind but also his sense powers. But without body there can be no sense activity. Hence the body too belongs to man's constitution.

But can we not say, with Averroes, that the soul is an impersonal intelligence, united with the body, say, of Socrates, in order to accomplish there that act which we call thinking? No, again, because such a union, being accidental, not essential, would prevent the act of thinking from being in truth the action of Socrates. Socrates would have to say, not: "I think," but instead: "It thinks," somewhat as we say, "It rains." Nor can we say, further, that intelligence is united to the body as motor, to move and guide the body, since thus it would follow that Socrates would not be a natural unity, would not have one nature only. [637].

But can then the rational soul be a spiritual thing, if it is the principle of vegetative and sense life? It can, because, to quote the saint, [638] "the higher a form is, the less it is immersed in matter, the more likewise does it dominate matter, and the higher does its operation rise above materiality." Even the animal soul is endowed with sense activity. Much more then can the rational soul, even as form of the body, dominate that body, and still be endowed with intellectual knowledge. [639] The spiritual soul communicates its own substantial existence to corporeal matter, and this existence is the one and only existence of the human composite. Hence, also, the human soul, in contrast to the soul of beasts, preserves its own existence after the destruction of the body which it vivified. [640] It follows, further, that the spiritual soul, when separated from its body, preserves its natural inclination to union with that body, just as naturally as, to illustrate, a stone thrown into the air still preserves its inclination to the center of the earth. [641].

Is there possibly only one soul for all human bodies? No, because it would follow that Socrates and Plato would be simply one thinking subject, and the one's act of thinking could not be distinguished from that of the other. [642].

Since each individual human soul has an essential relation to its own individual body, it follows that, by this essential relation, the separated soul remains individualized, and hence has a natural desire for reunion with that body, a reunion which, so revelation tells us, will become fact by the resurrection of the body. [643].

Is the rational soul the one and only form of the human body? Yes, because from this one form come both sense life and vegetative life, and even corporeity itself. If there were more than one substantial form in man, man would be, not simply one, but accidentally one. [644] Supposing many substantial forms, the lowest of these forms, by giving corporeity, already constitutes a substance, and all subsequent forms would be merely accidental forms, as is, to illustrate, the form we call quantity when added to corporeal substance. A form is not substantial unless it gives substantial being. [645].

Notice how, throughout these articles too, the saint insistently recurs to the principle of potency and act. "Act united with act cannot make a thing one in nature." [646] On the contrary, "only from act and from potency essentially proportioned to that act can arise a thing of itself one, as is the case with matter and form." [647] This principle of potency and act is the source of the wonderful unity in the Thomistic synthesis.

Is there not contradiction in saying that a form essentially spiritual can, nevertheless, be the source of corporeity? No, because superior forms contain eminently the perfection of inferior forms, as, to illustrate, the pentagon contains the quadrilateral. [648] The rational soul contains, eminently and formally, [649] life sensitive and vegetative, and these qualities are only virtually distinct from one another. There would be contradiction if we said that the soul is the immediate principle of act, intellective, sensitive, and nutritional. But the soul performs these acts by the medium of specifically distinct faculties. [650].

If the rational soul has as object the lowest of intelligible realities, namely, the sense world, what kind of body shall that soul have? Evidently a body capable of sense activity. [651] Thus the body is meant by nature to subserve the soul's intellective knowledge. Only accidentally, particularly as a consequence of sin, is the body a burden to the soul.

A summary of the principles which dominate the question of the natural union of the soul to body is found in the sixteenth of the twenty-four Thomistic theses. It runs thus: [652] This same rational soul is united to the body in such wise that it is the one and only substantial form of that body. To this one soul man owes his existence, as man, as animal, as living thing, as body, as substance, as being. Thus the soul gives to man all degrees of essential perfection. Further, the soul communicates to the body its own act of existence, and by that existence the body, too, exists.

To Thomists this proposition seems demonstrated by the principle of real distinction between potency and act, between essence and existence. Suarez, [653] who has a different understanding of this principle, holds that the proposition, "the soul is the one and only form of the body," is not a demonstrated proposition, but only a more probable one. Here again we see his eclectic tendency.

What we have said of the soul's spirituality, its personal immortality, its union with the body, shows clearly the degree of perfection given by St. Thomas to Aristotle's doctrine, which had been misinterpreted by Averroes as pantheistic. The precision Aquinas has given to Aristotle, particularly on the question of free and non-eternal creation, and on the present question of the soul, justifies the statement that St. Thomas baptized Aristotle. The principle of potency and act explains and defends these important preambles of faith. [654].