303. Human Nature (54). -- The soul is the substantial form of the body. It is the man, and not the soul alone, that is the proper object of scholastic psychology. Now man is a substantially compound being, of which the soul is the substantial form, the body the primal matter. This at once shows the solidarity of the two constituent elements of our being: their mutual relations are explained by the general theory of hylemorphism (286). Thus it is that the soul gives the body its substantial perfection, its actual existence, its life; and that it is, in the human nature ("id quod agit"), the formal principle ("id quo agit") of all human activities. The thirteenth century definitively rejected the Augustinian doctrines of the preceding period.^{1}

If, however, all the great scholastic doctors agreed in explaining human nature by the hylemorphic theory, each of them drew on his own metaphysics to decide whether the formal causality of the spiritual soul excluded the presence of other substantial forms in the composite individual, and notably of the "plastic mediator" or forma corporeitatis. It was in psychology, as may easily be understood, that the respective partisans of the unity and the plurality of forms fought their fiercest fights. The reader is already aware of the view St. Thomas defended in this matter, in spite of the determined opposition of his contemporaries (286): that view finally prevailed, but the contrary doctrine was never wholly abandoned.

The soul is spiritual and immortal. If scholasticism disowned Plato and St. Augustine in their theory of the union of soul and body, it availed of their arguments in establishing the spirituality of the soul. Those scholastics who claimed for human reason the power of demonstrating the spirituality of the soul -- and they were the great majority -- appealed, above all, to its independence as regards matter, in its highest operations.^{2} Breaking with Aristotle, scholasticism attributed immateriality not to the active intellect or to a faculty of the soul merely, but to its very substance; and since immortality has for its intrinsic foundation the immateriality of our intellectual cognitions, and of our volitions, what will survive the body is not the active intellect, sterile in its isolation (Aristotle), but the soul in the full enjoyment of its conscious life and the full exercise of its higher activities.^{3}

St. Augustine's waverings between traducianism and creationism had awakened echoes down into the twelfth century. But from the commencement of the thirteenth the scholastics appear to have taught unanimously that the direct and daily intervention of the Creator can alone call into existence souls destined to animate human bodies. There can be no need to observe that creationism has nothing in common with the Platonic doctrine of the preexistence of souls, nor with the system of Aristotle which makes the human body and the intellectus possibilis subject to the laws of natural generation, while attributing to the intellectus agens an ill-defined extrinsic origin (thurathen).

{1} The theory of the spiritus physicus, bequeathed to the Middle Ages by Grecian antiquity, was still maintained; but this spiritus was now no longer, as it had been with Alan of Lille for example, a third factor serving as a sort of connecting-link between soul and body; nor was it identified with the human soul as in the materialistic psychology of the Renaissance; it was conceived as springing from the informing principle, and disposing the brute matter for the activities of inorganic life.

{2} St. Thomas brings forward. this other argument, little in harmony with his thesis on the natural union of soul and body, and which seems very like a concession to traditional views: He remarks that the more the soul frees itself from the body, the more capable it becomes of the work of high speculation. Whence he concludes that death, or complete detachment from the body, cannot be for the soul the signal of its annihilation (Contra Gentiles, ii., 79. Cf. 243).

{3} More solicitous for philosophical truth than historical accuracy, the medieval doctors readily excused Aristotle, and forced the meaning of his theories. Speaking of the corruptibility of the possible intellect, ST. BONAVENTURE says: "Illud verbum Philosophi debet pium habere intellectum" (II. Sent., d. 19, a. s, q. i, ad 3. Cf. ST. THOMAS S. Theol., i., q. 89, a. 1 ad 1. Cf. 281).