Introduction to the Philosophy of St. Thomas Aquinas
In Aristotle's view the study of the soul is an integral part of the investigation of nature, in a way a preliminary to biology. We need not wonder, then, that Aristotle devotes comparatively small consideration to the operations of our highest, that is, our spiritual faculties, intellect and will. St. Thomas, whose almost every philosophical inquiry is undertaken in furtherance of a theological matter, gives much more attention to this part of his psychology. We shall follow his example. Believing, moreover, that the detailed analysis of the operations of the will is more suitably left to moral philosophy, we shall devote the greater part of our consideration of the spiritual soul to matters pertaining to the intellect. Indeed, it may well seem that we have given more space to problems of the intellect than one should expect in an introductory study. We felt it necessary, however, to go into some detail on several points, not only because they are too important to be dismissed with generalities, but also because for the most part they are too summarily treated in other manuals of comparable scope and purpose.
Aristotelian psychology - perhaps "anthropology" or the science of the human organism would be more exact - centers around the well-known affirmation that the soul is the form of the body. Its main preoccupation lies in determining the relationship between the two basic realities of which man is constituted. We have endeavored, on our part, to give this question the emphasis it deserves; above all, we have tried to make it very clear that in one way or another all of man's activity depends on this body-soul relationship.
Still, it must be admitted that to define the soul as the form of the body does not tell the whole story of man's nature, since the soul of man is not merely a form, but a form that can exist by itself. A pneumatology, if that is the word, or a science of spiritual being would therefore seem to be a necessary complement to the hylomorphic consideration of the soul, seeing that the study of the soul as form retains a strong biological impress to the end. In this additional undertaking Aristotle was both halting and obscure. St. Thomas was in a more favorable position, having before him the example of St. Augustine, himself the beneficiary of all those new discoveries of the soul made, or made possible, by revealed truth. St. Thomas, therefore, presents a forthright doctrine of mens or spirit as such, together with its unique powers and activities, like the power to reflect on and know itself, indirectly in its present condition, but directly and without intervening medium in the future state of separation from the body. This is the reason why we have stressed such matters as the knowledge by which the soul knows itself through itself, and the knowledge it has in the state of separation. Such questions together with their answers open up new vistas, reaching far beyond the horizons of Peripateticism.
But the psychology of St. Thomas goes even further, looking to the world beyond for the light that will discover the innermost structure of the human soul, for it is the light of revelation that discloses the mark of divine resemblance in the soul's being. Though more reserved than St. Bonaventure, who construes many aspects of man as the image of God, St. Thomas nevertheless believes that the ultimate explanation of our being lies in its being kindred with God. Homo ad imaginem Dei factus: man is made to the image of God. These, it should be remembered, are the words with which St. Thomas introduces his prologue to the Prima Secundae, in which he treats of the rational creature's return to his Principle and Beginning.