Summa Theologica

The soul is the form of the body, form being defined as that by which a thing is. The soul is what animates or gives life to the body. Form is also that which makes things different. What differentiates man from other creatures is his rational nature, derived from the intellectual principle which is his soul. All this reinforces the idea that the soul is united to body in a very intricate union. In fact, the soul is in each and every part of the body, informing it substantially. 

The soul’s power (the operation or work that it does) is distinct from its essence, as is true of every created thing; only in God are essence and power identical. Thus, unlike God, who has one single power through his essence, the soul is endowed with several separate powers. These powers are distinguished by their acts and objects. There is a natural order or hierarchy among them. The intellectual powers are superior to the sensitive powers, whereby we apprehend things through our senses. These are in turn superior to the nutritive powers, whereby the body receives nourishment from food. When the body dies, the sensible parts of the soul do not remain in it, but intellect and will do. 

Here Aquinas deals with the powers of the soul. The soul is divided into three parts:

nutritive (the principle of receiving nourishment from food)

augmentative (the principle of growth)

generative (the principle of reproduction)

The soul has different powers or senses, which Aquinas divides into exterior and interior. The exterior senses are sight, hearing, smell, touch, and taste; these senses depend on a bodily organ to do their work. The interior senses are common sense, imagination, estimative sense, and memorative sense. They do not depend on a bodily organ, and their purpose is to call things to mind in their absence so that the creature can make judgments and plans about them. For example, a sheep recognizes a wolf as dangerous and runs away from it, because its common sense (instinct) tells it that this is the right thing to do.

When the external senses operate, the perceived object causes a change inside the soul. In some senses, this is a natural change: For example, a person’s hand becomes warm by holding it close to the fire. In other senses, it is a spiritual change: For example, in sight, the eye receives an image of the object but does not physically change. 

This question outlines Aquinas’ theory of knowledge, based largely on Aristotle.

The intellect is a power of the soul, not its very essence (the latter is true only of God). The intellect has a passive and an active part. Before we understand anything, we have the potentiality toward understanding; we are like “a clean tablet on which nothing is written” (415). The active part of the intellect, the agent intellect, makes things actually intelligible by abstracting their form from their material conditions. Through this act of the agent intellect, our passive knowledge is made active, and the soul has understanding. The agent intellect helps us go from a knowledge of concrete particulars to a knowledge of abstract concepts. The agent intellect is ultimately moved by God; thus, we can say that our intellect is in potentiality to the active power of God. The passive part of the intellect is called the possible intellect.

God is necessarily part of the equation because our intellect is imperfect and “there must be some higher intellect, by which the soul is helped to understand” (417).

Memory and reason are powers of the intellect. To reason is “to advance from one thing understood to another, so as to know an intelligible truth” (421). Reasoning is the work we do in order to understand. In a broader sense, intellect and mind also describe the same concept.

Aquinas distinguishes a higher reason, which contemplates eternal things for their own sake, and lower reason, which disposes temporal things. Synderesis is the name for the habit of reason.

Conscience is an act of the soul by which it observes and judges his actions. 

Appetite, in its Latin root, means a seeking after or inclination toward something. Thus, the appetite is a power of the soul that desires or tends to something. There are two distinct appetitive powers in the soul: the sensitive appetite, which desires the things that are attractive to the senses; and the intellectual appetite, which desires the things apprehended by the intellect, the same as the will. 

Sensuality is “the appetite of things pertaining to the body” (429). It is further divided into two powers, the irascible and the concupiscible. The concupiscible has to do with seeking pleasure and avoiding pain, and the irascible has to do with resisting and overcoming obstacles. The two powers are related inasmuch as the irascible power seeks to safeguard the goods sought by the concupiscible power. The irascible power includes such passions as anger, hatred, and vengeance. The irascible and concupiscible appetites, which are among the lower parts of human nature, are subject to reason and intellect. 

Absolutely speaking, the intellect is a higher power than the will. This is because the intellect first grasps the end or goal (truth or the good) for the will to act upon. Nevertheless, the two powers work closely together, and we can say in a sense that the will can move the intellect as well as the intellect moving the will.

Our will is not predetermined, yet because we have a natural inclination toward God and the good, we may say that the will desires the good of necessity. This desire is not contrary to the will, but natural to it. The intellect has a more universal scope than the will, because the intellect looks at the whole or universal good, while the will looks at individual actions that will help achieve the good. Thus, the will is not programmed by necessity to choose one particular thing over another. In the next question, Aquinas will look more closely at the will’s freedom of choice.

The will desires all things under the aspect (or appearance) of good; thus, even evil is chosen as an apparent good.

As a creature endowed with intellect, man has the power of free choice. Moreover, only human beings act by a judgment rooted in the power of knowledge. Some things act without knowledge or judgment, but merely by a natural tendency, like a stone rolling down a hill. Other things act from a judgment that is natural instinct, like an animal avoiding a predator.

Free choice in an act, but it can also be described as a power of the soul. Free choice is subject to the grace of God, which helps it to choose what is good. Further, free choice belongs to the appetitive part of the soul. The intellect (cognitive power) proposes to the will what is to be chosen as means to the final end, then the will makes a free choice based on that information.

The soul knows bodily things through the intellect, which mentally extracts the idea of what the thing is from its physical nature. There is no need to posit, as Plato did, the existence of universal immaterial Forms through which the soul knows things. If this were true, then there would be no reason for the soul to be united to the body and to receive information through it. Nor does the soul have innate knowledge of things, as Plato claimed; rather, the intellect is like a blank slate, as Aristotle said, and it is in potency to all outside forms.

We get our intellectual knowledge from things perceived through our senses. The senses convert the objects of its perception into “phantasms” or mental images, and from these we abstract intellectual knowledge. Thus, it follows that if our senses are impaired (even momentarily, as through sleep), our intellectual knowledge will be hindered. 

In this question Aquinas presents his theory of mind—an account of the process by which the mind understands things.

Our knowledge proceeds from sense to intellect. The sense powers receive sensible types of objects, then convert these into phantasms (images). The active power of the intellect extracts, or abstracts, from these phantasms the intelligible type of the object, conveying its essential nature to us. From here, the process of reasoning can begin, which is a process of comparison, composition, and division, aimed at discovering the truth.

The senses perceive the particular, while the intellect perceives the universal. In sense knowledge, we move from the particular to the universal. However, in intellectual cognition the reverse happens: We move from the universal to the particular. We perceive first that a man is approaching us, before we perceive various details about him.

The intellect cannot err in the basic cognition of its object. If mistakes come about, it is further along in the reasoning process. Different human beings have different intellectual abilities, so we do not all understand everything to the same degree. This may depend partly on the aptness of the sensory organs.

We can understand multiple things, but not simultaneously, because the intellect cannot be informed by more than one form at once. Rather, we grasp complex ideas as a unity (under one single form). This is also true of God: He has a simultaneous knowledge of all things through the form of his own substance. 

In this question Aquinas presents his theory of mind—an account of the process by which the mind understands things.

Our knowledge proceeds from sense to intellect. The sense powers receive sensible types of objects, then convert these into phantasms (images). The active power of the intellect extracts, or abstracts, from these phantasms the intelligible type of the object, conveying its essential nature to us. From here, the process of reasoning can begin, which is a process of comparison, composition, and division, aimed at discovering the truth.

The senses perceive the particular, while the intellect perceives the universal. In sense knowledge, we move from the particular to the universal. However, in intellectual cognition the reverse happens: We move from the universal to the particular. We perceive first that a man is approaching us, before we perceive various details about him.

The intellect cannot err in the basic cognition of its object. If mistakes come about, it is further along in the reasoning process. Different human beings have different intellectual abilities, so we do not all understand everything to the same degree. This may depend partly on the aptness of the sensory organs.

We can understand multiple things, but not simultaneously, because the intellect cannot be informed by more than one form at once. Rather, we grasp complex ideas as a unity (under one single form). This is also true of God: He has a simultaneous knowledge of all things through the form of his own substance. 

Aquinas follows Aristotle’s doctrine that “the universal is known by reason, and the singular is known by sense” (461). Matter creates individuality in things, but our intellect understands a thing by abstracting its intelligible form (or type) from its material conditions. For example, when we look at a dog, we grasp it at once as “a dog,” and not merely as an assemblage of fur, teeth, etc. Thus, we know immediately the universal rather than the singular. However, after understanding the intelligible type, the intellect then turns to phantasms in the mind, and thus it arrives at a knowledge of the singular (this dog rather than dog in general).

Our intellect cannot actually know the infinite, because we gain our knowledge from sensible and material things. We can potentially understand infinitude in the sense that we can understand an infinite succession of things. It is true that we can know God, who is infinite; but in this life we only know him from his material effects, and not in his essence.

We can know contingent things (things that are uncertain or conditional), and we can know future things under certain conditions. For example, scientific knowledge of universal causal principles allows us to predict future events with some accuracy. However, only God knows the future considered in itself. 

Aquinas considers how we understand our own understanding. The intellectual part of the soul knows itself not by its essence, but by its act. In other words, we understand our own act of understanding, while it is happening. This is because in this life we cannot know spiritual things in their essence, and the intellect is a spiritual thing.

Aquinas’ other major point is that the intellect and the will are closely involved with each other; one is in a sense the principle of the other. Thus, what is in the will is also in the intellect, and thus the intellect understands the acts of the will. 

Here Aquinas turns his attention to whether, and how, the human soul can know spiritual substances—namely, the angels and God. In this life we cannot understand spiritual substances in themselves (in their essence). Through material things we can “rise to some kind of knowledge of immaterial things, but not to the perfect knowledge of them” (472). Although God is the first principle of all things, he is not the first thing known to the human mind. Rather, we first know material things, and from those we rise to a knowledge of God. 

Separated souls are those that have been separated from the body, or souls of the dead. What things are separated souls able to know? The difficulty of the question is that for Aquinas it is natural for the soul to be joined to the body—in contrast to Plato, who held that the soul merely uses the body for convenience. Aquinas concludes that although it is most proper and natural for the human soul to be united to a body, separated souls are able to know and understand things, albeit in a different way—namely, like the angels, by the “influx of the Divine light” (476).

Thus, separated souls are able to know other spiritual substances (devils and angels), each other, some singulars, some natural things, and the retain the knowledge acquired in this life. As to whether separated souls know what happens on earth, opinion is divided, but Aquinas sides with the view that the souls of the blessed do have knowledge of all that happens here. 

Aquinas argues the following points about the human soul: that it was created by God out of nothing, rather than coming directly from God’s substance; that it was created directly by God, and not through the angels; and that it was created in tandem with the body, not before. 

Aquinas strives prove the nobility and fittingness of the human body, and that the creation of the body is appropriately described in Genesis. The description of man as having been made from the slime of the earth reflects the fact that man’s body is made up of the four elements. God made the human body perfect according to the purpose that he set for it. All the members and senses of the body serve the higher operation of man’s understanding and show his nobler status compared with the plants and animals. 

God, for the perfection of human nature, created human beings as male and female. Man and woman are complementary, with woman a helper to man in the process of generation. The first woman was fittingly created from a rib of the first man to signify their close union and to prefigure the sacramental union of Christ and the church. 

Man bears the image of God, but since it is an imperfect image, there is no equality between man and God. Thus, it is best to say, with scripture, that man is made “to” God’s image, to convey that man approaches the divine likeness. Only the Son of God is a perfect image and likeness of God. The angels bear the image of God more perfectly than man, because their intellectual nature is more perfect.

Being an image of God means being imbued with a certain dignity. Man is the image of God chiefly in his intellectual nature—allowing him to know and love God—and secondarily in his ability to procreate. Thus, irrational creatures (such as heavenly bodies and other animals) are not the image of God, but even creatures that fall short of that image bear a vestigial likeness to him. Aquinas states: “Thus every creature is an image of its exemplary type in the Divine mind” (493).

The human soul reflects traces of the Trinity in its structure—for example, in the threefold faculties of memory, understanding, and will.

Aquinas considers the kind of knowledge that Adam, the first man, enjoyed in Paradise (the state of innocence before the Fall).

Although Adam did not see God in his essence (if he did, he would not have sinned), he knew God more perfectly and clearly than we do. Adam’s will and faculties were perfectly ordered to God. His lower powers were perfectly subject to the higher and he was able to contemplate God without being distracted by things of sense. Adam, before he sinned, was incapable of being deceived, having a divinely infused knowledge of all things that were necessary to his state of life. The Fall upset this balance, so that now we must reason our way to God from his sensible effects.

In sum, the first man was happy in Paradise, but not with that perfect happiness to which we are ultimately destined and which consists in the Beatific Vision. Adam enjoyed a state of natural, rather than supernatural bliss. 

Adam was created with God’s grace infused in him. Consequently, his moral inclinations were perfectly ordered to God. Passions and corresponding virtues existed in him, although not in the same way as in us. For example, temperance moderated lawful pleasure, not lust or concupiscence. Likewise, faith and hope existed for Adam, since he was not in possession of the perfect (supernatural) vision of God.

Aquinas asks whether the actions of man in the state of innocence had greater merit than ours. He concludes that Adam’s actions had greater merit in an absolute sense because he enjoyed a more perfect possession of grace. Our actions have greater merit in a proportional sense, however, insofar as good deeds are more difficult for us since our nature has been corrupted by sin. 

Man, in the state of innocence, had dominion over the animals. He did not need them for food or clothing or transport, but rather in order to know their natures as created by God. Animals perfectly obeyed man, even if different animals preyed on each other.

In the state of innocence, human beings would not have been equal in every respect, showing differences in bodily strength, beauty, and knowledge, among other things. Man was a social being from the beginning, and thus there would have been social relationships in which human beings were placed at the head of other human beings. Yet these relationships would not have been ones of domination, but rather of leadership and service. 

Original sin caused pain and death. Man, in the state of innocence, did not suffer pain, but he did experience change (he was passible). Man was susceptible to bodily danger, but he was preserved from it by his reason and by God’s Providence. Aquinas argues that man in the state of innocence was immortal, but he possessed this immortality not intrinsically through his body (because the body is naturally corruptible) but by his soul through the grace of God. The immortality was finite in the sense that it had to be continually replenished by taking nourishment. It was a natural immortality. The kind of immortality we will achieve in heaven is of a different, supernatural order and is perfect incorruptibility. 

Aquinas argues that propagation of the human species would have been necessary in the state of innocence, as it is for us. This was not to preserve the human race (because human beings were immortal), but rather to multiply it and fill the world. Propagation would have come about through sexual intercourse, but a version untainted by lust and better ordered to reason. 

Here Aquinas disposes of two erroneous notions: that children in the state of innocence would have possessed full strength of their faculties immediately after birth; and that women would not have been born. He argues that God disposes all defects for a greater good, including the natural growth of children’s abilities and faculties. God’s plan for the perfection of the universe included the male and female sexes and the procreative act as a natural endowment and activity of human beings. 

Aquinas argued earlier that the first man was created in a state of original justice—i.e., a fundamental moral rightness or rectitude before God. He now concludes that this state of original justice would have been passed along to man’s offspring, had he not sinned. However, the children would not have been confirmed in this state of justice—that is, ensured from ever falling into sin. Even if Adam and Eve had not sinned, their children or descendants might have sinned. This is because, unlike the angels, man’s choices are not binding forever; he has the power to reverse the course of his actions.

In the state of innocence, children would have had to progress in knowledge and the use of reason, because this is a part of human nature.

They would not have been born with perfect knowledge, but “in course of time they would have acquired knowledge without difficulty by discovery or learning” (523). 

Aquinas insists that Paradise (the Garden of Eden) was a physical place and not purely a spiritual state or metaphor. It is a spiritual reality founded upon a historical reality. Further, Paradise was perfectly suited to man as a composite of bodily and spiritual natures. Man was not created in Paradise; rather, he was created first, then placed there, so as not to suggest that his blessed state was a result of his own nature instead of being a gift of God’s grace.