Summa Contra Gentiles is less widely known and much less widely read than Saint Thomas Aquinas’s later, longer Summa theologiae (c. 1265-1273; Summa Theologica, 1911-1921). Summa Contra Gentiles is simpler in its structure and in that sense more readable and less involved, but the Summa Theologica has become better known, perhaps because it is more widely used in church dogmatics. Summa Contra Gentiles is the more philosophical of the two works, as its author intended, and more likely to be of more interest to the non-Catholic reader. It is an earlier work, but Thomas’s ideas did not change radically, and a comparison of the basic doctrines does not reveal any wide discrepancy.
Whereas Summa Theologica begins with an apologetic approach, explaining the relation of philosophy to theology and arguing for the existence of God, Summa Contra Gentiles begins immediately with God as he is in himself. As a work directed to the non-Christian, the reverse might have been expected. However, Summa Contra Gentiles is less doctrinal in style and does not base its arguments on a prior acceptance of Scripture as authoritative, as the Summa Theologica does. The earlier work is more directly metaphysical, defining the “wise person” as one who deals with the first beginning and the last end of the universe. Truth is conceived of as the final end of the whole universe, and the treatise begins directly with a consideration of the divine nature as that which must be delineated if one is to explain first and last things.
Thomas agrees with classical philosophy in holding that the chief aim of humanity is to achieve wisdom. In his case, however, this consists specifically of a knowledge of God. Because the Bible must be accepted as authoritative in order to be convincing, it cannot be used to prove any question about God’s nature. With Jews, of course, a Christian may use the Old Testament as a basis for argument, and even heretics may recognize the New Testament as valid evidence; they simply do not agree with the orthodox interpretation. For those who are neither heretics nor Jews, all argument must be based solely on natural reason. The first thing to establish is what mode of proof is possible where God is concerned. Some things true of God are beyond the scope of human reason, as, for example, that God is three in one. Other things, such as the unity and existence of God, are demonstrable under the light of natural reason. Yet human reason cannot go on to grasp God’s substance directly. Under the conditions of present natural life, the knowledge understanding can obtain commences with sense-data.
To discover anything true about God is exceedingly difficult, and not many have either the time or the natural capabilities for such arduous work. Some people devote themselves to business affairs and never study theology seriously. Furthermore, first of all, one must master philosophy, which means that a study of divine nature requires a lot of preparation. Thus, in one sense, it is a study better suited to old age, when some naturally disturbing influences have subsided. Theology is difficult, restricted, and demanding; therefore, faith was provided so that all people need not find out about God for themselves. It was necessary, Thomas argues, for the real truth about divine things to be presented to people with a fixed certainty by way of faith.
Reason and faith must agree, however, and Thomas begins by asserting that it is impossible for the truth of faith to be contrary to principles known by natural reason. No opinion or belief,...
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Thomas is sure, is sent to humanity from God as an item of faith that is contrary to natural knowledge. For one thing, although for human beings knowledge begins with sense objects, these retain in themselves some trace of the imitation of God. Here is Saint Bonaventure’s doctrine of the natural world seen as a sense world but also as one containing traces within itself of its supernatural origin as a creation of God. Thomas also affirms the use of the negative method, another traditional doctrine. People may have some sort of knowledge of the divine nature by knowing what it isnot.
Proofs for God’s existence appear in Summa Contra Gentiles, but they are in briefer form than in Summa Theologica and seem less fully developed. One might have expected this work, directed at pagans and not dependent upon Scripture for its arguments, to make more use of the “proofs.” Instead, the proofs receive less stress, and Thomas moves directly into a discussion of the divine attributes. He discusses in sequence God’s eternality, his freedom from potentiality, his lack of composition, and his incorporeality. All of these are rather directly stated as if they needed little expansion.
Summa Contra Gentiles appears to be the framework upon which Summa Theologica was finally built. The arguments need expanding, and more biblical material is included, but the structure is very much the same. In Summa Contra Gentiles, very few authors are quoted, and the argument is simply advanced in a straightforward way. Later, in Summa Theologica, Thomas attempted to blend a number of important views and to reach a more detailed conclusion. In the earlier work, however, he seems satisfied to provide the outline of the important questions and the basic structure of each argument. Little of great significance is changed in the later work, but the arguments receive a great many refinements, and the reasoning is made both subtler and more complex in order to deal with the multiplicity of views presented there.
Aquinas considers God’s understanding at length and describes its difference from humanity’s. God does not understand temporally but eternally. He does not understand by knowing an object directly but by knowing its intelligible counterpart in his own understanding. God’s understanding does contain a multitude of objects, but he understands all things at once and together. Propositional truth is also present in the divine understanding, and God also knows individuals, not merely universals. Nonexistent things are known by God, even though they never will become actual, and he knows individual events, contingent upon humanity’s action, as they will happen. In order to do this, God must know the motions of the human will as well as his own will, and through these he understands evil as well as good.
Aquinas agrees to the traditional self-sufficiency of God’s nature: God does not of necessity love things other than himself. Things outside God need him in a way that he does not depend on them. God’s will is free, subject to no external conditions, and has no cause other than his own wisdom. His goodness is the reason he wills all things, and in that sense it is possible to assign a reason for the choice of God’s will. Will, understanding, and goodness exist in God, but not passion, because that would indicate imperfection. There is love in God, but not such that he suffers from it or is subject to anything else because of it. God cannot, it is true, will evil, but such a limitation is no imperfection. God hates nothing, although his attributes are such that it is proper to describe him as “living.”
In contrast to this extended and direct discussion of God’s nature, philosophy considers humanity and the natural order as these things are in themselves. Philosophy makes no necessary reference to God, but the Christian faith considers natural beings, not in themselves, but inasmuch as they represent the majesty of God. Furthermore, Christians focus specifically on that in humans that is directly involved in their relation to God’s will. The other human qualities are not as important in the Christian view. Philosophers take their stand on the immediate and natural causes of things; but Christians argue from God as First Cause, indicating what things are revealed and what people can learn about the divine nature. Philosophically, one begins with creatures and then may be led to a knowledge of God; faith studies creatures only in their relation to God and so studies God first and creatures after that.
Turning then directly to God, Aquinas asserts that God’s power and his action are not distinct. They are not two things, and this view actually results in a stronger doctrine of necessary predestination here than Thomas was to adopt in Summa Theologica. God does not create the natural world out of anything preexistent, and therefore he does not create merely by moving material. The act of creation means bringing a thing into being without any preexistent material, not even potentiality. Nor is creation a successive movement. Creation takes place in an instant. A thing is at once in the act of being created and is created. Such a drastic form of creation is an action proper to God alone, and he creates directly with no intermediaries. God’s power extends to every possible thing, except to those that involve a contradiction.
In God there is an active power but no potentiality. Whatever would necessarily involve potentiality, those things are impossible to God. Nor could God make one and the same thing to be and not to be, because that would involve a contradiction. He cannot make a thing that lacks any of its essential constituents. His will cannot be changeable; he cannot cause what once was willed not to be fulfilled. On the other hand, God’s knowledge or understanding is bounded by no limits in its view. This means that God is essentially infinite, although all other things are limited. The infinite reach of God’s understanding means that his knowledge extends even to things that neither are, nor shall be, nor have been.
God needs nothing and depends on nothing other than himself; every other being is in his or her neighbor’s debt on God’s account. In all these matters, God is not a debtor to any creature, but a debtor to the fulfillment of his own plan. There is no absolute necessity for the being of any creature. The creature begins to exist in time exactly when God from eternity arranged that it should begin to exist. God brought into being creation and time simultaneously. Thus, questions that concern a “before creation” are improperly asked. There is no account to be given of why he produced a creature now, and not before, but only why the creature has not always been. Having thus been always willed, a new thing that has not always been may be produced by God without any change in him. However, if time has not always been, one may mark a nonexistence of time prior to its being.
Multiplicity and variety characterize creation, to the end that the perfect likeness of God can be found in creatures and in each according to his or her measure. Taken all together, they are very good, because the order of the universe is the finest and noblest creation. Of course, in created intelligences, both potentiality and actuality are present in a way in which they are not in God. The potential intellect in humanity does not subsist apart from matter but is intimately dependent on the body’s functions. In each person, it is individual, just as one’s body is individual. There is no common potential intellect that is the same for all people. Despite the individuality of the human intellect and its close association with the passive intellect, particularly with the functioning of the body, the human soul does not perish with the body but is capable of independent existence. However, this does not mean that the human soul is of the same substance as God, because they differ quite markedly in basic nature. Neither is the human soul an eternally existing thing nor is it transmitted by generation; it is, rather, brought into being by a creative act of God himself.
Aquinas’s description of the divine nature is metaphysical; his doctrine of the creation of the natural order can stand on its own logical ground. It fits into Christian doctrine, it is true, but Aquinas does not expect it logically to depend upon this, nor does he consciously derive his two doctrines from specifically or exclusively Christian materials.
Two objectives of the vast scheme remain: to consider the end of humanity and the created world in relation to God, and to consider finally what God can be said to have revealed. Using a quotation from the Psalms, Aquinas begins his discussion of the last end of humanity with the assertion that God will not abandon his creation once constituted. Every creature acts to attain some end, so that the natural world in this sense seems constantly directed toward the attainment of some goal. Furthermore, the goal desired is always some good; evil is a thing aside from the attention of an agent. In fact, the very cause of evil is something that in itself is good; and even when evil appears, it never cancels out completely the good upon which it is based.
Because the end of everything is always some good, the ordained end of all things is actually the source of all good: God. God is the end of all things in the sense that all rational creatures desire to be like God, to understand him. Happiness in any ultimate sense does not consist, for humanity, in bodily pleasures. Humans know, as rational creatures, that all final happiness lies in the contemplation of God. However, this happiness is not based on a general knowledge of God or upon the knowledge of God’s existence that is to be had by demonstration. The problem is that people cannot in this life see God as he essentially is, which means that the final happiness of humanity cannot be attained in this life. Nor can any created substance of its own natural power arrive at a point where it can see God as he essentially is. To achieve its aim in life, a created intelligence needs an influx of divine light enabling its intellect to be lifted up to see God. Yet even in seeing God, no created intelligence could comprehend the divine substance or see all things that can be seen in God. Nevertheless, this is not an exclusive affair; every intelligence of every grade can, by being lifted up, partake of the vision of God.
Those who do see God will see him forever, and in that final happiness every desire of humanity will be fulfilled. Because God is the cause of the activity in all active agents, God is everywhere and in all things. The progress toward humanity’s final goal, then, is within the scope of divine providence. The providence of God watches immediately over all individual things. This does not deny a freedom of the will because the action of divine providence is not direct but operates by means of secondary causes. However, the motion of the human will is caused by God and subject to his providence.
From this point, Thomas moves on to consider specifically the utility of prayer, the question of fate, miracles (which God alone can work), and the purposes for the giving of a divine law for human conduct. The divine government of humanity here on this earth is like paternal government because people’s acts are punished or rewarded by God. Of course, not all punishments or rewards are equal. There is a distinction between venial and mortal sin, the latter being material in determining final reward or punishment. Because people cannot attain happiness for themselves, they need divine assistance, or grace. The presence in people of grace causes people to love God and produces faith. Such grace is given gratuitously. People can, it is true, easily do good from time to time, but they need the assistance of grace in order to persevere in good action. People may be delivered from sin but only by grace.
All these things people need to know if they are to understand their final goal and the possibility for achieving it. Yet the human mind cannot of itself arrive at the direct vision of the divine substance. God cannot, Thomas has established, abandon his creation; therefore, revelation is necessary in order to show humans the way. God himself is prevented by his nature from descending to humanity, but here is the heart of Christian doctrine. For the Son of God, as a coequal member of the Trinity, is at the same time God and capable of descending to humanity to make the necessary revelation to humanity’s knowledge of its final end and the means thereto. Thomas began by addressing rational arguments to non-Christians, but the discourse is brought to the place where the Christian doctrine of revelation through Christ is considered to be necessary for the completion of creation’s plan.
Thomas, having laid the rational groundwork for considering the nature of Jesus, examines various theories of Christology and their adequacy. Revelation through an agent of God himself is necessary to the fulfillment of this rational plan, and now everything depends upon describing Jesus’s nature so that he is seen as fulfilling this role successfully. No one needs to be converted to Christianity by this means, but at least its rational basis can be examined. Thomas rejects Arian and Sabellian views as heretical, as orthodox Christians have done, and goes on to discuss each person of the Trinity and to work out a theory of their functions and relationships. Next, a theory of the Incarnation is developed. The human nature assumed by the Word (Christ) must be perfect in soul and body in every respect and from the instant of conception.
The need for sacraments and the doctrine of Original Sin are discussed. Because Thomas concludes with a discussion of the office of the minister and the resurrection of the body, one might almost forget that Summa Contra Gentiles was written for non-Christians. However, its non-Christian basis still remains: It aims to present Christian doctrine on the basis of arguments and materials that do not themselves depend for their validity on the prior acceptance of authority. Thomas had no intention of avoiding specifically Christian doctrines, but what he meant to do was to present them in the form of rational discourse, moving on from a theory of God and the nature of humanity to show the consistency of Christian doctrine with such a rationally developed view. Taking in as it does nearly every major metaphysical, theological, and ethical question, this work is truly a vast summa (summation), written to present Christian doctrine upon the basis of rationally structured argument.
Bradley, Denis J. M. Aquinas on the Twofold Human Good: Reason and Human Happiness in Aquinas’s Moral Science. Washington, D.C.: Catholic University of America Press, 1997. Bradley argues that Saint Thomas Aquinas was a theologian first and philosopher second. He contends that to avoid misinterpretation, Aquinas’s writings should be approached from a theological, rather than a philosophical, approach.
Chesterton, G. K. St. Thomas Aquinas. New York: Sheed and Ward, 1933. A superb introduction to the life and thought of Thomas, “the Angelic Doctor.” Aimed at non-Christian readers, or those with little experience in theology.
Copleston, F. C. Aquinas. Harmondsworth, England: Penguin Books, 1955. A scholarly yet accessible discussion of the philosophy of Thomas. Spends little time in dealing with Thomas himself but instead focuses on God and creation, body and soul, morality and society. The discussion of modern Thomism is dated. Copleston’s analysis provides insight into Thomas’s use of Aristotle (he notes that the ancients were concerned with how things came into being; Thomas was concerned with why).
Kenny, Anthony. Aquinas. New York: Hill and Wang, 1980. This volume in the Past Masters series covers Thomas’s life in fewer than one hundred pages. Thomas’s theories are explored, including his conception of Being (which Kenny believes is hopelessly flawed) and his notion of the nature of Mind (which Kenny praises for the questions Thomas asks). Latter chapters introduce the reader to medieval categories of thought, but Thomas the Christian is almost submerged.
McInerny, Ralph. Ethica Thomastica: The Moral Philosophy of Thomas Aquinas. 1982. Rev. ed. Washington, D.C.: Catholic University of America Press, 1997. This work is one of the finest introductions to Thomas’s moral philosophy. Covers selected themes in Thomistic moral thinking, including moral goodness, judging good and evil moral actions, work of virtues, functions of conscience, and relation of ethics to religious belief.
McInerny, Ralph. St. Thomas Aquinas. Boston: Twayne, 1977. An accessible study of Thomas’s thought in chapters dealing with Aristotle, Boethius (whose philosophy was introduced to modern times through Thomas’s writings), and Platonism. In a chapter on the tasks of theology, the author explains Thomas’s distinction between believing and knowing. The book is filled with examples and includes a useful chronology of Thomas’s life plus a short, annotated bibliography.
Sigmund, Paul E., ed. St. Thomas Aquinas on Politics and Ethics. New York: W. W. Norton, 1987. An introduction to Thomas, with eighty pages devoted to pertinent excerpts of Thomas’s work, newly translated by the editor. Selections are generally quite short and range from Thomas’s writings on government to selections from his treatise on God in Summa Theologica. Excerpts from background sources are also presented, with the remainder of the volume devoted to interpretations of Thomas.