Summa Theologica

Religious teaching aims to inform us about God as he is in himself and as he relates to creation, being its beginning and end. Aquinas considers the question of God’s existence. The statement “God exists” is self-evident in the sense that God is existence itself. God’s existence must be argued, however, because it is not self-evident to us, allowing for assertions of his non-existence. Aquinas rejects the idea that one cannot demonstrate God’s existence because it is a matter of faith, instead arguing that God’s existence can be demonstrated through natural reason the cause of various effects. Aquinas concedes, however, that we can know God as he is absolutely in his essence. Among the many ways to describe God, he is “that thing than which nothing greater can be conceived” (11).

Aquinas presents his five ways to prove the existence of God. They are:

1.  From motion: Whatever is in motion is put in motion by something else, but because infinite regression is impossible, a first mover must exist, which is God.

2.  From efficient causes: Everything that happens is caused by something else, but because infinite regression is impossible, a first efficient cause must exist, which is God (13).

3.  From possibility and necessity: In the world we find things that are contingent (conditional, or possible to be and not to be). Everything that exists was brought into existence by something else that previously existed, but because infinite regression is impossible, something necessary must exist, and this is God.

4.  From degrees or gradations: In the world we judge things to be more or less good, true, and noble, but this implies that there is an exemplar from which to judge—one that is the best, noblest, and truest. This exemplar is God.

5.  From the way nature is governed: All actions are directed toward an end, and they seem to achieve their end not by chance but by design (e.g., animals acting on instinct). Thus, some ultimate intelligent being must exist by whom all things are ordered to their end. This is God.

In summation, all things that are changeable or capable of defect must be traced back to an immovable, perfect, self-necessary first principle, which is God. 

Aquinas begins his discussion of the attributes of God, ranging over several questions. We cannot grasp who God is in his essence. For the most part, we understand him negatively—in terms of what he is not. The first negative way of understanding God is in terms of his simplicity. God is not a body; he is purely spiritual. Bible passages which seem to attribute physical aspects to God must be understood as figures of speech describing his spiritual powers. Just as God is not a body, so also God is not composed of matter and form. He is pure act, without the potentiality that exists in matter (see Index of Terms).

God is the same as his essence or nature. He is life itself. This is in contrast to created things composed of matter and form, which consist of an essence and accidental qualities which inhere in it. Man is not the same as his humanity, but God is his very Godhead. God is pure being. Aquinas writes: “In God existence is not an accidental quality, but subsisting truth (17). Not only is God his own essence, he is his own being. All created things receive their being from something else, but God has his being in himself.

God has no accidents (see Index of Terms). As absolute being, God can have nothing added to him, just as heat can have nothing in addition to heat. There can be nothing caused in God—as, for example, laughter is caused in man—because God is the first cause of all things. Although wisdom, virtue, and other qualities are predicated of God, they are predicated differently than they are of us.

Aquinas discusses the absolute simplicity of God. God does not have separate parts to him; he is a unity. He does not undergo change, and his essence does not differ from his being. Complex things have component parts, which pre-exist them; but God is the first being and first cause. There is no part of him which is not God. Something that enters into the composition of something else does not itself act, but the composite acts; for example, a hand does not act, but a man acts by his hand. God is neither a composite nor part of a composite because he is first act. 

The second attribute of God to be examined is his perfection. Since God is the efficient cause of all things, he must be most perfect. God lacks nothing; he has within himself the perfection of all things. Creatures can be like God. However, while we may say that some creature is like God, we cannot say the opposite, that God is like a creature; the likeness is not mutual. This is because a mutual likeness may exist between things of the same order, but not between a cause and an effect.

Before considering the goodness of God (the subject of the following question), Aquinas considers the good in general.

Aquinas argues that good and being are the same. The only difference is that good “presents the aspect of desirableness” (23). The mind first perceives that a thing is before it perceives anything else about it, so being precedes good as an idea. Good, however, can precede being in the sense of its nature as an end or final cause for things. Although being is good and good is being, we may sometimes speak of non-being as a good and desirable, insofar as it involves the removal of an evil.

Every being, as being, is good. No being, as being, is evil; it is only lacking good (see Themes). Since good is that which all things desire, good is the final end or cause of all things. It thus relates to appetite, or the capacity for desiring something. Aquinas references St. Augustine, “We are because God is good” (26). The notion of good is involved with the concepts of mode, species, and order—in which are part of everything God made (26). Following earlier thinkers, Aquinas divides the good into the categories of fitting (virtuous), useful, and pleasant. 

Goodness belongs especially to God. Aquinas states: “All things, by desiring their own perfection, desire God Himself” (28). We can know God in different ways and to different degrees: as he is in himself; through some participation in his goodness; and in our having a natural inborn desire for him. God is the supreme good, but “supreme” does not imply his comparison with things in another genus because God is outside genus. Supreme also does not imply that anything has been added to God to make him more, which would compromise God’s simplicity. That God is “supreme good” means only that other things are deficient in comparison with him. Only God is good through his own essence. All other things are good by virtue of participating in this perfection of goodness. Qualities that in lesser beings belong as accidents belong to God essentially—such as power, wisdom, etc. 

God is infinite—meaning not bound by the limits placed on a thing by matter, substance, or place. Things other than God can be relatively infinite, but not absolutely infinite. For example, wood is relatively infinite since it has the potential to become an infinite number of shapes. Although God has infinite power, he cannot make anything to be absolutely infinite, because this implies a contradiction; any created thing is by nature finite. 

Aquinas looks more closely at the concept of infinity as it applies to God. God is in all things, because he works in all things. Since God is being itself, he necessarily causes being in other things, just as fire causes things to ignite. God not only causes things to be, he maintains and preserves their being. Aquinas states: “Therefore as long as a thing has being, God must be present to it” (35).

God is everywhere; he is in all things as giving them being and power. In this sense, he fills every place, albeit not in the sense that a physical thing does. This power of God means that he can be in one or in many places. He is indivisible—meaning that his power extends itself to everything in every place. God is wholly in all things, in the same sense that the soul is in every part of the body (36). Aquinas rejects the conclusions of heretical thinkers who asserted that material things were evil (and thus God was not in them) or that inferior things were not subject to God’s providence. We speak both of God being in all things and, conversely, of things being in God, since they are contained by him. Both figures of speech express a truth about God and creation. He is in all things, and all things are in him. 

Aquinas considers whether God is subject to change. God is changeless (immutable):

1) because he is pure act, with no potency at all, and anything that is changed is in some way in potency (see Index of Terms)

2) because anything that changes, changes in one of its parts only; and there is no composition in God, since he is altogether simple

3) because everything that changes acquires something that it did not have before; but God is infinitely perfect. Bible passages that speak of God as moveable must be understood metaphorically.

Next, Aquinas considers whether only God is immutable. He concludes: “God alone is altogether immutable, while, every creature is in some way mutable” (39). This is clear from the fact that created things are brought from non-being into being by God, while God is the uncaused cause. 

Eternity is outside of time; it has no present, past, or future, and is “simultaneously whole.” God, the eternal being, has no past, present, or future, and thus no beginning and no end. He exists in an eternal Now. We understand eternity in negative terms: as the absence of time, time being “the numbering of movement by before and after” (41). Just as we progress from corporeal things to the knowledge of spiritual things, and as we understand divine things through metaphors, so we come to a knowledge of eternal things by means of time. God’s eternity follows from his immutability. Because he is not subject to change, he possesses eternal life. Further, God is his own eternity, just as he is his own being or essence. In this he resembles no other being.

God alone is eternal, but creatures may receive immutability and eternity from him. Logical and mathematical propositions are not eternal in themselves, since they derive from the divine intellect. Aquinas asserts that in Hell, true eternity does not exist, but rather endless time. Time and eternity are separate things. Eternity is whole, while time has parts—a before and an after. Eternity is the measure of permanent being, while time is the measure of movement. Eviternity (aeviternity) is an intermediate state between eternity and time. It is associated with things that have a beginning but are changeless, such as the heavenly bodies, angels, and the soul. 

Before considering the unity of God, Aquinas looks at unity in general. To say that something is one is merely to negate division; “one” is not a quality in addition to being. The being of anything consists in its unity or oneness. However, this is different from one as the principle of number. We can demonstrate in three ways how God is one:

1) His simplicity. God alone is his own nature. Therefore, there cannot be many Gods.

2) His perfection. If there were many Gods, they would differ from each other, and thus some would not have complete perfection.

3) From the unity of the world. The first principle which reduces all the diverse things of the world into one order should be only one; and this is God. 

Up to now Aquinas has considered God as he is in himself; now he will consider God as he is known by creatures. God is able to be known by the human mind. If this were not so, human beings would not be able to find their ultimate fulfillment, which is to know and love God. Thus, the blessed souls in heaven see the essence of God. Although there is a wide distance between God and man, the two relate to each other as cause to effect, and act to potency. In this way, there is communication between them.

Our minds can grasp God since God created them. This is because in order to see anything, there must be some likeness between the seer and the thing seen. God cannot be seen by bodily senses or by the imagination, but only by the mind. God is both the author of our intellectual power and the thing that the mind sees. The human mind cannot see the essence of God by its own natural power, but only with the aid of God’s grace. This is because the thing known is in the knower according to the mode of the knower, and God’s mode of being far exceeds that of human nature.

In order for the human mind to see God, it must be raised up by grace, enlightening the mind. Some minds will see God more perfectly than others, according to their level of love and desire.

Even though the human mind is capable of seeing God, it will not see every aspect or action of God. In this life, we are able to see God as the cause of his effects, rather than what God is in his essence. This because our earthly knowledge takes its starting point from the senses.

Grace gives us a more perfect knowledge of God than what we have through natural reason. Human knowledge consists in seeing images of sensible objects, then forming abstract concepts from them. Even here grace plays a part, strengthening the natural light of reason. In prophetic visions and dreams, divine knowledge is conveyed to us directly through sensible images. 

We can legitimately give names to God, but with the understanding that these names do not describe his very essence. Instead, the names draw analogies with earthly beings with which we are familiar. Philosophers have proposed different theories about the names and descriptions we apply to God (e.g., God is good). One theory holds that they are negative affirmations—e.g., “God is not evil”; another, that they mean God is the cause of those qualities in creatures.

Aquinas reaches a different conclusion: The names point to real qualities in God, but we arrive at them only through our knowledge of how those qualities are reflected in creatures. Thus, when we say “God is good,” we mean, “Whatever good we attribute to creatures pre-exists in God” (64). Thus, what is signified by the names (goodness, wisdom, etc.) belongs properly to God, but that we understand them in a way that applies to creatures, who reflect the attributes of God in an imperfect way.

The names applied to God are not synonymous with each other. While the divine essence is one simple reality, the names as applied by us point to separate aspects of that reality. Further, the names we apply to God do not mean exactly the same thing when applied to him as when applied to creatures. Some names of God (e.g., “Creator”) imply his essence, referring directly to his actions, while others (e.g., “Lord”) refer to a relation to his creatures.

When it comes to God, we cannot know his essential nature, but only his effects on the created world. The name that is most proper to God is the name given to him in the book of Exodus, “He Who Is.” This is because:

1) it refers to being itself, and only God is being itself

2) it is universal, referring to what God is in his essence

3) it refers to being in the present, and this properly applies to God who exists in the eternal now

Aquinas asserts that we can make affirmative propositions about God, not only negative ones (e.g., “God is not evil”). We can say what God is and not merely what he is not. Since we cannot know God as he truly is in this life, we form different conceptions of him reflecting different aspects of his nature. For example, we speak of God as the Creator or as the Supreme Judge. 

Aquinas maintains the idea that God knows all things, including all events and the individual qualities of his creatures.

God has the most perfect knowledge of any being. To know something is in a sense to comprehend it within oneself, and thus to enlarge one’s being. This is what gives a knowing being (such as man) greater “amplitude and extension” (76) than a non-knowing being (such as a plant). The more separated from matter a thing is, the more it is capable of knowing. Thus, God has the highest and most perfect knowledge because he is non-material in the highest degree.

God understands himself through himself. In him, the intellect and the thing understood are the same. This is because he is pure act—with no potentiality, as exists is in our intellects when they are about to receive knowledge. In contrast to our way of knowing, God’s mind is not perfected by the thing it knows (its intelligible object), but is its own perfection.

In addition to understanding himself, God perfectly comprehends himself. Comprehension means that one thing holds and includes another. In God’s case, it means that nothing is hidden from himself. He understands everything there is to know about himself in the most complete and perfect way. Since God is pure actuality, without any potentiality, then his understanding is identical with his substance.

To have general knowledge is to know what all things have in common, and to have proper knowledge is to know things as distinct from each other. Aquinas asserts that God must have proper knowledge of things, because this is a more perfect knowledge. He has not only general knowledge of things—e.g., there are so many dogs in the world—but specific knowledge—e.g., what makes this dog different from that dog.

God sees all things at once. Whereas we can only consider things one at a time, God sees everything in one single act. He knows all things through his essence, which comprehends all things. God’s knowledge is the cause of all things. Aquinas compares God’s knowledge to an architect’s plan, which the architect puts into action through his mind and will. In a similar way, God causes all things by his intellect and will.

God’s gaze extends over all time, to all things that are, will, or might be. To know a thing perfectly is to know everything that can happen to it. Therefore, God must know evil things, because he must be aware of the corruption and evil that may come to good things. Good defines evil since evil is a privation and not a subsisting thing (see Themes).

Although God’s nature is non-material and perfect, his knowledge is not confined to the universal. The Bible clearly describes God as knowing our hearts. God knows individuals because we human beings know individuals, and any perfection we have exists in a perfect form in God.

Next, Aquinas examines whether God can know contingent future events—things which are uncertain or conditional. God gave human beings free will, thus their actions are contingent. Scripture asserts that God knows the hearts of men; therefore, God must know contingent things in the future. God’s sight extends over all present and future things, since he dwells in the eternal Now. 

A proposition is a logical statement in which a predicate is affirmed or denied. Propositions are typical of the analytical, step-by-step way human beings think. God knows the contents of all propositions because God knows whatever is in his creatures. God does not have to reason out those propositions as we do, but instead knows them in a direct, comprehensive, and simultaneous manner.

Since God’s nature is unchangeable, so is his knowledge. Aquinas states: “from the fact that a thing exists in some period of time, it follows that it is known by God from eternity” (89). The fact that God knows contingent things means that he knows how things change, not that his knowledge itself changes. 

By “ideas” Aquinas means the forms or underlying principles of things, existing apart from the things themselves. “Idea” is a philosophical concept originating from Plato and his theory of transcendental forms. Aquinas uses it to answer the question of whether ideas exist in the mind of God. He concludes that yes, ideas do exist in the divine mind because God planned the world rationally—it did not come about by chance—and thus there was an idea underlying it. Whenever an agent acts to fulfill a form (idea), that form or idea pre-exists in the mind of the agent. Ideas exist in God’s mind in such an intimate manner that they are identical with his essence. There are many things in creation, and each thing corresponds to an idea in the divine mind. 

The subject of knowledge is truth. Thus, Aquinas proceeds to discuss the nature of truth. Truth resides primarily in the mind, and secondarily in things. Aquinas emphasizes that the true represents our judgment of what is. Truth is in relation to our mind. Our mind tends toward truth just as our appetite tends toward good.

Aquinas discusses the work of the mind in terms of “composing and dividing” (95)—that is, the analytical thinking we do when we consider facts and their relationships. Aquinas contrasts this type of operation with the kind of simple, direct knowledge that we get from sense impressions. Truth not only involves simple correspondence between our mind and reality, but also an awareness that this is going on, implying an analytical process.

Aquinas concludes that “being” and “true” are convertible terms. The true is being insofar as it is knowable, and conversely each thing is knowable insofar as it enjoys being. This is not to say that the two terms “being” and “true” are interchangeable, but rather that the underlying reality that they express is the same.

While the good has to do with appetite and desire, the true points us toward what is to be desired in the first place. Not only is truth in God, but it is in him in the highest degree, and thus he is “the supreme and first truth” (97). This is because in him, being and intellect and the act of understanding are all the same.

Is there only one truth by which all things are true, or many separate truths? There is a sense in which all things are true by one primary truth, the truth of God. Nevertheless, considered from the point of view of the many minds of creatures, there are many truths. Mathematical truths are eternal only insofar as they exist in the eternal mind of God.

Is truth unchangeable? Aquinas concludes that truth can change in our minds, since they are mutable; for example, our belief about a thing may change. (This does not imply that the thing itself changes, merely that our understanding of it changes.) The truth in God’s mind, however, is unchangeable, because his mind is unchangeable and there is a perfect conformity between things as they are and his mind. 

Having examined the nature of the true, Aquinas now examines the nature of the false, asserting that falsity exists in the mind and not in things. Falseness cannot exist in the works of God but can exist in the works of man to the extent that they fall short of the divine plan (Aquinas relates this to the idea of sin).

When our senses deceive us, the falsity is to be ascribed less to the senses than to the mind, which reports the false data. The mind cannot be deceived about basic nature or form of a thing, but it may be deceived about its accidental qualities. The first operation of the mind is to grasp the essence of a thing, and it cannot be deceived about this. However, the next level of cognition, reflecting on the essence itself, may produce deception and falsity. 

Christian language attributes the words “life” and “living” to God. Aquinas examines what this means. He starts by defining life as such. Life properly speaking means the power of movement. This movement may be a physical movement, or it may be an act, such as understanding and feeling. All other things that have movement, such as water or the celestial bodies, are said to have life only in a figurative sense.

Life is not an operation (something we do) but part of our being. Although living things pursue certain activities, this is not the essence of what it means to live. Life exists in the highest degree in God. This is because he alone has his final end and principle of being within himself; in all other beings, these things are implanted in them by nature. Our movements are in a sense beyond our control, but God’s movements and operations (such as understanding and will) are all of his own will and design. 

Intellectual beings (humans and angels) have a disposition toward good as grasped through the intelligible form of things. It is the will that allows the mind to attain the object of its appetite. In God, the will is the same as his being and his act of understanding. God wills not only himself, but other things. Not only do natural things will their own good for themselves, they desire to spread the good to others. This is truer of God. All things that God wills are willed for the sake of his goodness, as their final end. God’s will is unchangeable, because there is no change in God’s knowledge or substance. Although God wills that certain things change, this does not mean that his will changes.

Does God dictate what will happen? If the divine will imposes necessity on everything that happens, then this destroys man’s free will. Aquinas’ solution is that “the divine will imposes necessity on some things willed but not on all” (116). God’s will is always fulfilled; yet evil exists. Aquinas concludes that while God does not will evil, he permits various evils in order that a greater good may come of them (see Themes). We might say that evil can accidentally lead to some good.

Because love is the natural object of the will and appetite, and God has will, we must assert that he also has love. God loves all things, since everything that exists is good. Whereas we love things as a response to their goodness, God’s love creates goodness in things. God especially loves those creatures that are more in need of his love—e.g., sinners and the weak. 

In God, justice and mercy are united and integrated. They are complementary, not opposed. The kind of justice that belongs to God is distributive justice, “whereby a ruler or a steward gives to each what his rank deserves” (124). Thus, God rules the universe much like a person who governs a family or country. Mercy, in God, is more like an action or effect than like an emotion or passion. When God enacts mercy, he does not negate his justice, but goes above and beyond it. It is like bestowing a gift; as when God pardons a sin. Aquinas states: “Hence it is clear that mercy does not destroy justice, but in a sense is the fulness of justice” (126).

Aquinas asserts that all things are subject to divine providence, defined as God’s ordering of all things toward an end. However, God’s overarching providence does not exclude secondary causes. There are two parts or phases to providence: the planning of the order of things, and their execution (or government). Providence imposes necessity upon some things but not upon all. 

In this section Aquinas confronts the thorny issue of predestination, much debated among theologians since. Aquinas asserts that predestination belongs to God as part of his providence. Some persons are destined to heaven, others to hell. However, this does not in any way obviate man’s free choice of the will as regards his actions in this life. Thus, predestination is not predetermination, in which there is necessity in the end result. In fact, human beings can further the effects of predestination by offering prayers for souls. 

Aquinas sheds light on the phrase “book of life” which is found in scripture apparently referring to the eternal destiny of human beings. Essentially, it is a metaphor expressing God’s knowledge of whom he has predestined to eternal life in heaven. Aquinas asserts that it is possible for persons to be blotted out of the book of life.

In God there is active (as opposed to passive) power in the highest degree. He is omnipotent, in the sense that he can do all things that are possible absolutely, in terms that make sense logically. (Anything that implies a contradiction in terms would be excluded from the things that God can do, because God is the author of reason. For example, it is not possible for God to erase the past.) Aquinas states: “God’s omnipotence is particularly shown in sparing and having mercy, because in this is it made manifest that God has supreme power, that He freely forgives sins” (146). 

For Aquinas, happiness is primarily intellectual. Happiness exists in God in the highest degree, insofar as he possesses the highest degree of perfection and intelligence. Aquinas states: “For nothing else is understood to be meant by the term happiness than the perfect good of an intellectual nature, which is capable of knowing that it has a sufficiency of the good which it possesses, and to which it belongs that good or ill may befall, and which can control its own actions” (150). Since happiness is the highest and perfect good of an intellectual nature, God as Intelligent Being possesses it in the highest degree. Both happiness and God can be said to be our final end, inasmuch as happiness constitutes our enjoyment of God.