The purpose of Thomas Aquinas’ philosophy was to express Greek philosophy in Christian terms. (It must be remembered that the study of psychology was at this time contained within the field of philosophy). The result of this compromise we will look at later, but first let us examine Aquinas’ theories in psychology.

If you were to ask Aquinas how do we know what we do, he would answer you by saying: sensation. That is, the body and soul working in harmony together receive stimulations from the external world. This is possible since the soul has the natural ability to take sensations, to sort them out, and to determine which sensations belong to which objects. By this means of associations one gains a knowledge of the objects around him.

We must notice here his emphasis on sensation. Sensation can only come to a person from material objects. Thus, it follows that it would seem impossible to know the spiritual.

Nevertheless, Aquinas maintains that there is within man a natural desire to know God. At this point we would think that this natural desire, which is placed within all men by God, must be in vain since man can not know God Who is Spirit. To this he would say that this is not the case at all for the following reasons. First, one can know God by means of His works in creation. These works act upon material objects which one can sense with the soul. Thus, one can know God indirectly. Second, one can know that these works are of God since the very nature of man’s soul is oriented towards good; notice not only the Good God, but anything which is good.

Man, who has a desire to know God, can know God in this life although that knowledge is imperfect. The corruption of the body can not affect the soul if it permits itself to be guided by reason. The means by which the soul is able to do this can only be by the work of grace. Man can not attain to the knowledge of God by his own efforts. Therefore, if man permits his reason, which is enlightened by the grace of God, to be his guide, he will attain that knowledge. Only when man does this is he acting in accordance with God’s will or invitation, and thus he is virtuous.

Why man strives for the attainment of the knowledge of God is because that is happiness for him. God is the source of man’s goodness and happiness. To know the good means that man will do it because that results in man’s happiness. However, if man willfully rejects doing the good, he sins. Man tries not to sin because it may result in punishment both from without and from within. Punishment comes from without by means of the civil authorities. And, punishment comes from within as a result of the conflict in the soul between the natural desire of goodness and sin.

Aquinas’ psychology differed from the Greeks’ in the following points. First, although the greeks spoke of a natural desire of all men to seek a god, they did not speak of grace because they denied the total depravity of man and they were not seeking God but rather an idol. Second, they did not speak of an individual conscious life after death in which man’s imperfect knowledge becomes perfect. Third, they did not speak of sin because they held to the principle of what we call today “situation ethics”. Fourth, that God permits sin in that man of his free will might reason to seek the good, and thus love and serve God of his own free choice.

Aquinas’ psychology was like Greeks’ in the following aspects. First, both held to the same composition of the soul; refer to part II “Conflict”. Second, both maintained that the union of body and soul is for the good of the soul. Third, both said that the soul is immortal, in other words, not able to die. Fourth, both concluded that man’s reason must and is able to guide man to goodness and happiness which he desires to seek. Fifth, both acknowledged the fact that outward conformity to civil authorities is necessary to avoid punishment.

However, Aquinas’ psychology is not Scriptural. God does not give a grace which is common to all men and which enables them to desire to know God. This we all know and can clearly see when we study Scripture in Its entirety. Aquinas knew that man apart from the grace of God holds the Truth, which is made manifest to him in creation, down in unrighteousness. The result of trying to harmonize philosophy and theology, as we have seen in the case of Aquinas, is a grace freely given to all, an invitation to salvation by means of knowing God, and a god who is dependent upon the creature for the ultimate choice.