Vol I No. 7
Daily Thought

Whether the Soul is a Body?

by William J. Martin


  aw Jan Van Eyck (1395-1441) — Portrait of a Woman

Whether the soul is a body?


Objection 1: It would seem that the soul is a body. For the soul is the moving principle of the body. Nor does it move unless moved. First, because seemingly nothing can move unless it is itself moved, since nothing gives what it has not; for instance, what is not hot does not give heat. Secondly, because if there be anything that moves and is not moved, it must be the cause of eternal, unchanging movement, as we find proved Phys. viii, 6; and this does not appear to be the case in the movement of an animal, which is caused by the soul. Therefore the soul is a mover moved. But every mover moved is a body. Therefore the soul is a body.


The soul is the moving principle of the body. But the soul does not move unless it is moved. It cannot impart or share what it does not have since it can only yield an effect if it possesses the effect is contained within the cause. What is hot gives heat. What is moved moves. Only God moves but is not moved by another. However, when a body moves, it is moved by its soul. The soul is in the body. The soul is a mover that is moved in and through the body. Only bodies move and thus the soul must be a body if it is moved. Thus the soul is a body.


Objection 2: Further, all knowledge is caused by means of a likeness. But there can be no likeness of a body to an incorporeal thing. If, therefore, the soul were not a body, it could not have knowledge of corporeal things.


All knowledge is an effect of something similar or like it. Knowledge begins with what is closest to us in the external and visible world. But a body is not like any incorporeal thing. It must generate its like or what is similar to it. Bodies impress upon the soul a likeness. So when we come to know, the cause is found in bodies and the likeness is of bodies. If the soul were not a body it could have no knowledge of corporeal things. For in order to register the impression and to come closest to its likeness it must be a body. Therefore the soul is a body.


Objection 3: Further, between the mover and the moved there must be contact. But contact is only between bodies. Since, therefore, the soul moves the body, it seems that the soul must be a body.


Between what moves and what is moved there must be a contact or a mediator. But there can be contact only between bodies. For if the soul is not a body that body cannot have contact with it. Bodies are what we understand as substances that either contact with one another or expand and isolate from one another. If the soul moves the body, it must be a body since if it were not, it could not have contact with and move the body.

On the contrary, Augustine says (De Trin. vi, 6) that the soul “is simple in comparison with the body, inasmuch as it does not occupy space by its bulk.”


St. Augustine tells us that the soul is simple when compared to the body. It does not occupy space by its bulk. For example, there is no expansion or contraction of the soul in a body. We don’t say that the soul expands and fills more space. We don’t say that it contracts and becomes less and smaller. The soul is not bodily in this way. Its nature is not measured or determined by quantity. We don’t say that more soul refers to a larger amount of soul or that a larger amount of soul will ensure greater joy or happiness.


I answer that, To seek the nature of the soul, we must premise that the soul is defined as the first principle of life of those things which live: for we call living things “animate,” [*i.e. having a soul], and those things which have no life, “inanimate.” Now life is shown principally by two actions, knowledge and movement. The philosophers of old, not being able to rise above their imagination, supposed that the principle of these actions was something corporeal: for they asserted that only bodies were real things; and that what is not corporeal is nothing: hence they maintained that the soul is something corporeal. This opinion can be proved to be false in many ways; but we shall make use of only one proof, based on universal and certain principles, which shows clearly that the soul is not a body.


The soul is the first principle of life in all things that live. Things that are alive have souls. Things that are not alive do not have souls. We find life through two activities, knowledge and motion or movement. The Pre-Socratic philosophers thought that soul or the principle of life was some material substance because only bodies were real things. So Thales said that Water is the cause of all that is or that lives. Anaximander said that the first cause is Unbounded Space. Anaximenes said that all is air, and so forth. For these thinkers what is not corporeal or bodily and material is nothing. So they believed that the soul is a body or is corporeal.


However, it is manifest that not every principle of vital action is a soul, for then the eye would be a soul, as it is a principle of vision; and the same might be applied to the other instruments of the soul: but it is the “first” principle of life, which we call the soul. Now, though a body may be a principle of life, or to be a living thing, as the heart is a principle of life in an animal, yet nothing corporeal can be the first principle of life. For it is clear that to be a principle of life, or to be a living thing, does not belong to a body as such; since, if that were the case, every body would be a living thing, or a principle of life. Therefore a body is competent to be a living thing or even a principle of life, as “such” a body. Now that it is actually such a body, it owes to some principle which is called its act. Therefore the soul, which is the first principle of life, is not a body, but the act of a body; thus heat, which is the principle of calefaction, is not a body, but an act of a body.


Now the soul is not every principle of vital action. For there are material movers like the eye that are involved in generating eyesight. However, these bodily movers are not the first principle of life. What this means is that material causes cannot explain and define the nature of a substance’s being. Water, fire, air, and so forth do not explain a creature’s true being. To be living does not belong to bodies as bodies since then every body would be a living thing and a principle of life. But those creatures that are alive are alive because of an act or a series of acts that congeal in the respective soul of each creature. So the soul is the act or the activity of the body. It is what enlivens and quickens the body through movement. As the prime mover of a body it brings it into being and sustains it through lesser movers. It is the principle of life as applied to particular creatures. Thus it moves a vegetable plant as a vegetative soul. It moves an animal as a sensitive soul. It moves man as an intellective soul. In all cases we can see that the soul as the first principle is an activity that ensures the creatures well being.


Reply to Objection 1: As everything which is in motion must be moved by something else, a process which cannot be prolonged indefinitely, we must allow that not every mover is moved. For, since to be moved is to pass from potentiality to actuality, the mover gives what it has to the thing moved, inasmuch as it causes it to be in act. But, as is shown in Phys. viii, 6, there is a mover which is altogether immovable, and not moved either essentially, or accidentally; and such a mover can cause an invariable movement. There is, however, another kind of mover, which, though not moved essentially, is moved accidentally; and for this reason it does not cause an invariable movement; such a mover, is the soul. There is, again, another mover, which is moved essentially—namely, the body. And because the philosophers of old believed that nothing existed but bodies, they maintained that every mover is moved; and that the soul is moved directly, and is a body.


To be moved means to pass from potency to act, from potential being to actual being. But if this process goes on indefinitely then we can find not unchanging and stable cause of all things. We would go on forever in motion. But that motion might be defined and understood there must be an unmoved mover in whom the motion stops and finds its ultimate cause and meaning. All things that are moved give themselves over to movers who bring them into a state of perfection. All things that are moved finally return to the Unmoved Mover as the source of thought and understanding, which is always a conclusion and not an activity. This means that the Unmoved Mover or God knows all particulars in themselves and in relation to one another as a unified whole of unchanging understanding. God moves essentially. Created souls move accidentally. Bodies move essentially. God and bodies by nature move essentially or according to their natures. Created souls move accidentally, which is to say that they move along with bodies. The soul moves the body as rowers move a boat. The body moves just as the boat moves. The soul or the rowers move along with it without any necessity. A vegetative soul, or a sensitive soul, or an intellective soul are things apart from bodies as the principles of life. The soul is immobile, incorporeal, and it is not in a place. Movement and change do not belong to the soul in itself. God moves but does not change. Bodies move and change. Souls do not move and do not change as souls. This is to say that they are the same in essence or nature. What changes is their quality or their character.

Reply to Objection 2: The likeness of a thing known is not of necessity actually in the nature of the knower; but given a thing which knows potentially, and afterwards knows actually, the likeness of the thing known must be in the nature of the knower, not actually, but only potentially; thus color is not actually in the pupil of the eye, but only potentially. Hence it is necessary, not that the likeness of corporeal things should be actually in the nature of the soul, but that there be a potentiality in the soul for such a likeness. But the ancient philosophers omitted to distinguish between actuality and potentiality; and so they held that the soul must be a body in order to have knowledge of a body; and that it must be composed of the principles of which all bodies are formed in order to know all bodies.


         The likeness of created things exist in man’s soul potentially but not actually. They are potentially known in the mind in a way suitable to the human soul. That is to say that all created things are potentially knowable and known in the soul that tries to understand their natures intellectually and not sensibly. The ancients thought that the soul had to be a body with all the parts of all created bodies in it if the bodies on the outside were to be known in man’s soul on the inside. But what they failed to see is that all things can be known potentially. Potential knowledge is that kind of knowledge that understands things intellectually and by way of abstracting for the sake of the soul’s perfection in the body. Knowledge is not perfect identy of one being with another.


As one author puts it: The soul knows bodies through the intellect by a knowledge that is immaterial, universal and necessary, although only God can understand all things. The cognitive soul has the potential to form principles of understanding and principles of sensation. Individual objects of our knowledge are not derived from Platonic forms but rather from the mind of God. Intellectual knowledge is formed by a conjunction of the passive senses and the active intellect. It is impossible for the intellect to understand anything without the mind forming phantasms, that is, mental images. (Spark Notes, T. Aquinas,


Reply to Objection 3: There are two kinds of contact; of “quantity,” and of “power.” By the former a body can be touched only by a body; by the latter a body can be touched by an incorporeal thing, which moves that body.


         Bodies touch bodies and this is quantitative contact. There is however a kind of contact whereby a body can be touched by a power that moves it intellectually. To be moved intellectually means that bodies are moved by causes and reasons that are transcendental. Bodies are moved by souls. Bodies are moved by principles of life that summarize and describe the movement that ensures their creation and preservation. These principles of life are abstracted from creatures as conclusions. Yet these conclusions are at the same time the causes and movers that moves bodies but are not essentially but only accidentally moved by them.