Aquinas: Christian Aristoteleanism
(Adapted from Garth Kemmerling’s “Philosophy Pages,” http://www.philosophypages.com/hy/3n.htm#fivw and Peter Kreeft’s “The First Cause Argument,” quoted at CERC http://catholiceducation.org/articles/apologetics/ap0168.html.)
The most profoundly influential of all the medieval philosophers was the Dominican Thomas Aquinas, whose brilliant efforts in defence of Christian theology earned him a reputation as "the angelic teacher." His willingness to employ rational argumentation generally and the metaphysical and epistemological teachings of Aristotle in particular marked a significant departure from the neoplatonic/Augustinian tradition that had dominated so much of the middle ages. Aquinas showed the church that it was possible to incorporate many of the "new" teachings of "the Philosopher" (Aristotle) without falling into the mistaken excesses of "the Commentator" (Ibn Rushd), and this became the basis for a lasting synthesis.
For Aquinas, theology is a science in which careful application of reason will yield the demonstrative certainty of theoretical knowledge. Of course it is possible to accept religious teachings from revealed sources by faith alone, and Aquinas granted that this always remains the most widely accessible route to Christian orthodoxy. But for those whose capacity to reason is well-developed, it is always better to establish the most fundamental principles on the use of reason. Even though simple faith is enough to satisfy most people, for example, Aquinas believed it possible, appropriate, and desirable to demonstrate the existence of god by rational means.
Five Ways to Prove God's Existence
Anselm's Ontological Argument (an attempt to prove the existence of god by a priori reasoning from the content of the concept of god) is not acceptable, Aquinas argued, since we are in fact ignorant of the divine essence from which it is presumed to begin. We cannot hope to demonstrate the necessary existence of a being whose true nature we cannot even conceive by direct or positive means. Instead, Aquinas held, we must begin with the sensory experiences we do understand and reason upward from them to their origin in something eternal. In this vein, Aquinas presented his own "Five Ways" to prove the existence of god.
The first four of these ways are all variations of the Cosmological Argument.
· The first way is an argument from motion, derived fairly directly from Aristotle's Metaphysics:
q There is something moving.
q Everything that moves is put into motion by something else.
q But this series of antecedent movers cannot reach back infinitely.
q Therefore, there must be a first mover (which is god).
· The second way has the same structure, but begins from experience of an instance of efficient causation; i.e. so far as we know, everything we experience has been caused to be what it is by something else.
· The third way relies more heavily upon a distinction between “contingent” and necessary being: everything we experience can exist, or cannot exist; nothing we know exists because it must.
· The fourth way is a variety of Moral Argument. It begins with the factual claim that we do make judgments about the relative perfection of ordinary things. But the capacity to do so, Aquinas argued, presupposes an absolute standard of perfection to which we compare everything else.
In all of its forms, the Cosmological Argument is open to serious challenge. Bertrand Russell, for example, argued that if the second premise (“Everything that moves is put into motion by something else.”) is wholly and literally true, then the conclusion must be false: it appears to be a self-refuting statement akin to the Liar’s Paradox.* This criticism is not fair to Aquinas: the second premise refers only to things which are in motion; the “first mover” is itself unmoved. If, on the other hand, it is possible for something to move without being put into motion by another, then why might there not be hundreds of "first movers" instead of only one? In fact, Aristotle, whom St. Thomas follows closely on this matter, variously argued on this basis that there were as many as 47 or 55 gods. Others point out that it is by no means obvious the Aristotelean notions of a "first mover" or "first cause" bear much resemblance to the god of Christianity. So even if the argument succeeded it might be of little use in defense of orthodox religion. On the other hand, “it’s a pretty thick slice of God … much too much for any atheist to digest.” (Kreeft)
· The fifth way is the Teleological Argument: the order and arrangement of the natural world (not merely its existence) bespeaks the deliberate design of an intelligent creator. Although it is an argument by analogy which can at best offer only probable reason for believing the truth of its conclusion, this proof offers a concept of god that most fully corresponds to the traditional elements of medieval Christian theology. Since its empirical basis lies in our understanding of the operation of nature, this line of reasoning tends to become more compelling the more thorough our scientific knowledge is advanced. The resurgence of interest today in the Intelligent Design discussion is perhaps evidence of this.
The Created World
Since the nature of god can be known only analogically by reference to the created world, Aquinas believed it worthwhile to devote great attention to the operation of nature.
Aquinas argued that the intellect is a higher faculty than the will in virtue of its greater degree of independence from the body. As the agent of knowledge, the human intellect comprehends the essences of things directly, making use of sensory information only as the starting-point for its fundamentally rational determinations. Although not all of Aquinas's contemporaries recognized, understood, or accepted this view of human knowledge, it provided ample room for the development of empirical investigations of the material world within the context of traditional Christian doctrine.
* The Liar’s Paradox:
If I say to you, “I am a liar,” I am making a “self-refuting” statement: I’m contradicting myself. If my statement is true, and I really am a liar, I must be lying when I tell you I’m a liar – in which case, I’m not a liar. If my statement is false, then I am not a liar – but I’m lying when I tell you I am. Either way, I’ve shot myself in the philosophical foot. 8^)