The Natural of Human Person in Saint Thomas Aquinas

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What is to be said about the union of soul and body? The soul, the principle of intellectual life, is the form of the body. Every human being has his or her own soul; and there is not one universal soul for all human beings, as some erroneously thought. There is just one soul in every human being; but the intellectual soul in men and women is capable of the sensitive and nutritive activity of plant and animal souls respectively. There is no other substantial form in human beings except the intellectual soul. The soul is united to its body because the soul derives its knowledge initially through the bodily senses. The human soul is joined immediately to its body, there being no connecting link between the two. The soul is present in the whole body and in every part of the body.[4]

- The faculties of soul

A faculty is the power of the soul to perform a specific operation. The faculties of the soul are distinct from its essence. There are several faculties of the soul which are distinguished according to the operations which they produce and the objects toward which they are oriented. Some faculties serve the others; in humans, for example, the senses serve the intellect which draws its ideas from the data furnished by the senses, and the intellect serves the will by guiding it. Some faculties, like the intellect and will, are to be found only in the soil; but the vegetative and sensitive faculties are rooted in the composite of soul and body. The latter can be exercised only as long as the composite lasts, that is, until death.

Thomas distinguishes five general categories within the faculties of the human soul: the vegetative, the sensitive, the appetitive, the locomotive and the intellectual faculties. Humans have some faculties in common with plants and animals; but some are proper to themselves. Humans have vegetative faculties in common with plants and animals. The vegetative faculties have, as their primary purpose, the inception and protection of life through generation, growth and nutrition. Humans have sensitive faculties prizing the senses of sight, hearing, smell, taste and touch, and the four internal senses which are the common sense, the imagination, the estimative faculty and the sense memory. The operations of the estimative faculty and sense memory are analogous to those of the intellect, but they fifer by reason of the particular character and material limitations of their objects. Over and above the vegetative and sensitive principles of activity, men and women have two faculties which are the operational powers of intellect and will, of knowledge and volition. Actually, men and women have two intellects, the passive of possible intellect and the active intellects. Both are faculties of the soul. The passive or possible intellect is called by this name because it receives its knowledge. It is, as it were, a tabula rasa, a blank page, on which nothing is written at the beginning of an individual’s existence. The active intellect abstracts the universal content of the data presented by the senses and impresses it upon the passive intellect. Perhaps we might compare the active intellect to a secretary who transcribes information from a book (sense data) onto the pages of a notebook (the passive intellect). However, it is the passive intellect which actually knows in virtue of the universal content abstracted from the sense data by the active intellect.

There are several things which seem to be distinct intellectual faculties, but really are not. Memory is one of them. Memory is a function of the passive intellect which preserves the ideas of things. Intelligence and reason do not denote separate intellectual faculties, but rather different acts of the passive intellect. Intelligence is a simple, direct knowledge of the truth, like understanding that the whole is equal to the sum of its parts. Reason is the gradual apprehension of the truth whereby the intellect proceeds from one thing known to another, like reasoning from the contingency of creatures to the existence of God. The higher and lower reasons which Augustine distinguished are not separate faculties. The higher reason, according to Augustine, contemplates eternal truths while the lower reason thinks on temporal things. The speculative and practical intellects are not different faculties; rather, the former designates the intellect insofar as it simply considers the truth, while the latter denotes the intellect insofar as it directs human activity. Synderesis is the habit of the first principles of morality by which we are inclined to do well and avoid evil. Conscience is an act of the intellect, the faculty of knowledge; it is the application of knowledge to act, the practical judgment of the intellect as to what is right and wrong. Next Thomas turns to the appetitive powers in human beings. In all creatures, he maintains, there is a tendency, a thrust, a driving force toward that which perfects, and is good for, the creature in question. In those things which lack knowledge, this tendency is called a natural appetite. In those things which have sense knowledge, such as animal, in thrust is called a sensitive appetite. In those things which have intellectual knowledge, such as men and angels, this thrust, or driving force is called an intellectual appetite or will. Thus, men and women have two appetites following upon their knowledge: an intellectual appetite or will, corresponding to their sense knowledge; and a sensitive appetite, corresponding to their sense knowledge.

The human will necessarily seeks what is good, that is to say, what fulfills desire and affords happiness. However, the will is free to choose among particular goods presented to it by the intellect. These particular goods are not good from every point of view; hence, they do not draw the will irresistibly. The intellect moves the will in the sense that it presents to the will what is good and desirable and moves it as an end. On the other hand, the will moves the intellect in the sense that is applies the intellect to the consideration of this or that object.[5]

- The activity of the soul

The activity of the soul proceeds immediately from the faculties of the soul. At this point, however, St. Thomas considers only the activity of the intellect. Because of its ethical significance, the activity of the will and sensitive appetite is dealt with later in the treatise on morals in the second part of the Summa.

How does the soul understand material things which are beneath it? The process of knowing begins when we contact a material object through the external senses, that is to say, when we see or hear or touch it. What we sense in this way is singular and concrete. A sensible image or phantasm of the object is produced