Thomas Aquinas: Summa Theologiae

Explanation and Analysis of the Document

We begin by calling attention to the scholastic genre in which Aquinas wrote. This logically meticulous genre first inquires into a disputed point; thus Question 1, Article 1 asks, “Whether, besides philosophy, any further doctrine is required?” It proceeds to discuss the known negative answers to the question, such as “Objection 1: It seems that, besides philosophical science, we have no need of any further knowledge.” Afterward, the writer presents the affirmative view, introduced by “On the contrary” or “I answer that” and then refutes each negative answer in sequence, such as “Reply to Objection 1.” Frequently Aquinas substantiates both the negative answers and his own positive positions with traditional authorities, including biblical passages, statements by church fathers, creeds, and quotations from councils, as well as “the Philosopher,” namely, Aristotle.

Treatise on Sacred Doctrine

Question 1, Articles 1–6

At the outset Thomas’s purpose in the Summa theologiae becomes immediately apparent: to integrate theology and philosophy without subordinating theology to philosophy and without reducing either of these two sciences (scientia, or species of knowledge) to the other. While both theology and philosophy are necessary for understanding God, theology is the queen or “chief of the sciences,” served by philosophy as its necessary handmaiden. Thomas’s opening six articles make one of his most notable and controversial contributions to Christian theology: the distinction between a natural knowledge of God accessible to all humanity and a special knowledge of God accessible to the faithful. The former knowledge encompasses philosophy and the other nontheological sciences, while the latter knowledge equals “sacred doctrine,” or theology. Both natural knowledge and sacred doctrine constitute “sciences,” since each employs reason, logic, and evidence, but they are grounded upon two different sets of axioms. The axioms of natural knowledge constitute the information gained from the five senses, while the axioms of sacred doctrine constitute the information gained from the Bible. Because God is the creator of the physical world and the ultimate author of scripture, both sciences are the logical outcrops of different forms of divine revelation, which can be called “natural revelation” and “special revelation.” Sacred doctrine is both “practical” and “speculative,” insofar as the relevance of some theological matters pertains directly to daily life while the relevance of others pertains to eternal life and will become apparent only in the hereafter. Since wisdom orders things according to their highest governing principle and since the truths God has supernaturally revealed are said truths, sacred doctrine alone is properly called wisdom and amounts to one unified science. Though theology and philosophy amount to two radically different ways of knowing, they do not contradict each other but rather cohere with one another, for both are fountains of scientia from the same divine wellspring.

Aquinas admitted that a certain happiness in this life can be achieved by the exercise of our natural powers, such that the unbeliever can realize the highest goal proportionate to human powers (the bonum ultimum). The existence of this goal and the means for achieving it are discoverable by philosophy. However, this bonum ultimum is still incomplete and imperfect, as humans must move beyond the natural to the supernatural goal of their existence. This supernatural goal (the summum bonum) is the final good, which cannot be known by unaided reason but only through theology. Thus the natural end, insofar as it cannot satisfy humanity, points beyond itself to the supernatural and satisfactory end. In seeking the natural, insisted Thomas, humanity is heading in the right direction but not traveling far enough. In other words, the natural end is imperfect because it is incomplete, not because it is wrong. Complete and perfect happiness is found in God alone.

Question 1, Articles 7 and 8

Sacred doctrine, for Thomas, is “a matter of argument” that necessarily complements philosophy. This is because the human mind unaided by scripture can reach only the vestibule to faith, while sacred doctrine allows us to move from the vestibule into the house of God. Theology is a higher science than philosophy owing both to the certainty of its data, as human perception can err but scripture cannot, and to the superior excellence of its object of study, namely, God. Thomas noted that theology utilizes logic not to prove scripture—in terms of either its doctrinal validity or its historical reliability—which he regarded as a futile enterprise, since God is already known to be truthful, but to formulate coherent doctrines from scripture and to defend their rationality.

Question 1, Article 9

If God is incomprehensible, as Aquinas believed, then how can the Deity ever be described, much less studied, using human language? The answer, says Aquinas, is through metaphor, a notion that has since been styled the “principle of analogy.” For God’s creation of the world points to a basic analogy of being between God and the world—there exists continuity between God and the world as a result of the expression of the being of God in the being of the world. Thus it is valid to use “material,” “corporeal things” as metaphors for God. In so doing, theology does not reduce God to the level of corporeal things; instead, it affirms that there are “similitudes” between God and corporeal things, which allow the latter to serve as pointers to God. Moreover, metaphor allows only persons who are spiritually receptive to receive the truth, since they are unlikely to abuse it, while truth’s inherent ambiguity hides it from the “unworthy.”

Question 1, Article 10

In Article 10 we find the classic articulation of Aquinas’s hermeneutic (methodology for interpreting scripture), known as the quadriga on account of the four “senses” conveyed by every biblical “word” or passage. The term quadriga originally referred to a four-horse chariot. Just as the chariot needed all four horses to advance in a straight line, so scripture needs all four senses to lead people down the straight path to eternal life. First, the “historical or literal” sense denotes the plain, factual meaning of the text. Second, the “allegorical sense” refers to the abstract spiritual principle embodied by the text. This sense was often followed in place of the historical sense when interpreting commands regarding ceremony, diet, and dress in the “Old Law,” or Mosaic Torah, which the New Testament declared no longer binding on Christians. It also trumped the historical sense when the literal reading affirmed something contrary to God’s perfection, such as God’s commanding the slaying of various Canaanite peoples. Third, the “moral” or “tropological” sense designates the text’s lessons for the believer’s ethical and devotional life. Fourth, the “anagogical sense” alludes to the elements of the text that foreshadow things that, though not yet having obtained, will obtain in the glorious new heaven and new earth.

Treatise on the One God

Question 2, Article 3

Although God is properly the object of theological investigation, this does not imply that nothing about God can be known through natural revelation. In fact, Aquinas argues that the existence of God can be indisputably proved five times over via philosophy alone. Through these proofs, even a person who had never heard of Christianity could deduce that God exists. These quinque viae (five ways), or five proofs for God’s existence, stand as perhaps Aquinas’s most enduring legacy; their soundness has remained a matter of lively debate among professional philosophers and theologians to this day. All five ways appeal to human experiences of the natural world, surmising that these experiences could not happen apart from the existence of God. In short, God can be known naturally as the necessary cause of his effects in the natural order.

The first way is “the argument from motion,” predicated upon the observation that many things in the world are constantly changing or “moving.” For anything in the natural world that is moving, it must have been moved by something already moving. That is to say, natural things do not just move on their own; they are moved by something else. So for the motion of any natural entity, there is another moving entity that caused its motion; if that entity is natural, there is another moving entity that caused its motion. Accordingly, when we trace these causes backward, we find a whole chain of moving things lying behind the world as it is at present. But since an infinite regress is impossible, there must be a single moving thing at the beginning of the chain. However, this original moving thing cannot be something in the natural world, or else it would need to have been moved by something else. Therefore this original moving thing at the beginning of the chain must be supernatural, which, Aquinas notes, “everyone understands to be God.” Within this argument, Aquinas introduced a significant Aristotelian distinction between two modes of being: potentiality and actuality. In every movement, something potential is becoming actual. But no potency can actualize itself, and thus the actualization of any potency requires a previous actuality. For this reason, the ultimate “first mover, put in motion by no other,” or Unmoved Mover who set the natural world in motion, must be actus purus (pure actuality).

The second way is “from the nature of the efficient cause,” predicated upon the observation that everything that comes into being, regardless of whether or not it moves thereafter, has been brought into being by something else. But everything in the universe has come into being. Consequently, the first thing in the history of the universe requires an efficient, or productive, cause, but this cause cannot be anything in the universe, since at that point nothing else in the universe existed. Therefore, this “first efficient cause,” “to which everyone gives the name of God,” must transcend the space-time universe.

The third way is “taken from possibility and necessity,” predicated upon the observation that some things exist contingently while other things exist necessarily. In other words, it is logically possible for some things to come into existence or to go out of existence, even if those things neither came into existence nor will go out of existence. Such things are called contingent. On the other hand, it is logically impossible for other things to come into existence or to go out of existence; they simply exist necessarily. But then the question arises: Why do contingent things exist at all? For unlike necessary things, which are self-sustaining by their very nature, contingent things could cease to exist and so do not sustain their own existence. Hence Aquinas contends that every contingent thing depends for its existence on a necessary thing. All this leads to the central issue: What about the set of “things in nature,” namely, the universe itself? Is it contingent or necessary? Notice here that Aquinas is not asking whether or not the universe, in fact, came into existence, as he realized that apart from scripture (which is not part of natural revelation and thus is off-limits to this argument), no evidence was available in his day to establish whether the universe had a beginning. (In fact, Aristotle held that the universe never came into existence.) Rather, Aquinas is asking whether or not it is logically possible for the universe to either begin to exist or cease to exist. Since not one but both of these are logical possibilities, it follows that the universe cannot sustain its own existence. Hence there must be a necessary being outside the universe, namely, God, who sustains the universe in existence.

The fourth way is “taken from the gradation to be found in things,” predicated upon the existence of such human values as goodness, truth, and nobility. However, we recognize that some human goods are better or worse than others, and even the greatest human goods are always capable of improvement. Such gradations or value judgments require an objective standard or yardstick against which they are measured. Since humans cannot, by definition, reach the greatest goods, as there are always potentially goods just a little bit better, human societies could not have devised this objective standard. Hence this objective standard must be the character, or nature, of God himself. (Even though male pronouns are used for God in English translation of the Summa, the original Latin does not specify gender, and Thomas regarded God as beyond gender distinctions.)

The fifth way is “taken from the governance of the world,” predicated upon the clear purposes that unconscious natural processes (for example, planetary motion) and objects (for example, plants) seem to contain, such as maintaining the order of the cosmos, growth, reproduction, and the like. As unconscious entities, they could not have given themselves these purposes. For this reason, “some intelligent being” must have instilled various purposes within these entities. Because no animal or human intelligence could have instilled such purposes, the intelligent being under discussion can only be God.