Much has been said of the 13th-century philosopher, Thomas Aquinas, from both secular as well as religious critics alike. For instance, Bertrand Russell once wrote with respect to Aquinas that he “cannot. . . feel that [Aquinas] deserves to be put on a level with the best philosophers either of Greece or of modern times” . This is due to Aquinas’ apparent prior commitment to the truth of the Catholic faith before he even begins to philosophize: “If he can find apparently rational arguments for some parts of the faith, so much the better; if he cannot, he need only fall back on revelation. The finding of arguments for a conclusion given in advance is not philosophy, but special pleading” .
Protestant philosopher Gordon H. Clark has suggested that Aquinas rejected the rationalism of Augustine and Anselm in substitute for Aristotelianism as the foundation of the Roman Catholic church . Furthermore, that since Aquinas attributes all of our knowledge as being abstracted from our sensations, and hence, his arguments for the existence of God are hinged off of this level of empiricism, “Thomas. . . cannot pass from the first mover to the Father, Son, and Holy Ghost” .
Francis Schaeffer even suggests that “[t]hanks to Thomas Aquinas, the world and man’s place in the world was given more prominence than previously” . In other words, Aquinas in his rejection of the depravity of mankind allowed for the possibility of perfection apart from God. Thus, Aquinas wrongfully used reason as “an absolute rather than a tool” . These criticisms and others among Protestant evangelicals predominately (although some Catholic thinkers aren’t dismissed), I do not think are legitimate reasons for rejecting the valuable apologetic (among other aspects) found in Aquinas’ thought.
Here, I only wish to present a few aspects of Aquinas’ thought which I think are valuable for all Christians to consider – both Protestants and Catholics alike . To begin our discussion:
Aquinas on Faith and Reason
G.K. Chesterton once rightfully asked this question: did Thomas bring Aristotle to Christ or Christ to Aristotle?  Aquinas recognized the importance of Aristotle’s thought with respect to Christian thought, in the fact that “[o]ne cannot question that [Aquinas] reconciled Aristotle to Christ” . However, as Craig Bartholomew expounds:
But is that transformation sufficiently radical, or is there still much in the structure of his thought where he has brought Christ to Aristotle? We see how this synthetic structure works, for example, in the doctrine of God – a theological rather than a philosophical doctrine, to be sure. Reason can enable us to see that God exists, revelation tells us who he is” .
Hence, Aquinas in his exposition of faith and reason doesn’t separate them but rather formally distinguishes them from each other. As Norman Geisler writes, “they are related, but the relationship is not coercive” . Specifically, reason does not coerce faith – if it did, then faith would not be a free act of the will. “Faith, then, is defined as ‘that habit of mind whereby eternal begins in us and which brings the mind to assent to things that appear not.’ Faith differs from science in that its object is unseen. Faith also differs from doubt, suspicion, and opinion in that there is evidence to support it” .
John Hick has a few noteworthy comments on this distinction. Particularly, that faith, according to Aquinas, presumes a position between knowledge (scientia) and opinion (opinio) and “accordingly falls on a common scale with them; and since they are both concerned with propositions, so also is faith” . This is due in part to faith’s concern with a propositional attitude – i.e., assenting to [theological] propositions. Moreover, “[these] propositions which faith believe, or at any rate those that are of faith absolutely, i.e., that can be accepted only on faith, are of a special kind” . Particularly, that these propositions express “mysteries”; i.e., the truth of them can never be immediately evident to us and must therefore be accepted on the basis of authority.
Furthermore, while Aquinas sees the meritous nature of faith, he also carefully examines the limited use of reason. According to Aquinas, the human intellect is lacking and divine revelation is essential due to of the five following reasons: (1) the depth and subtlety of the object [God], who is far from being an ordinary sense object; (2) the weakness of human intellect in its initial operations; (3) the length of time required to learn the things needed for a conclusive proof; (4) the fact that some people lack proper personality to engage rigorous philosophical pursuit; and (5) the lack of time for philosophy beyond the pursuit of the necessities of life.  To finish on Geisler’s point:
Aquinas’s view of the relation of faith and reason is a unique blend of the positive elements of both rationalism and fideism, or presuppositionalism and evidentialism. He stresses the need for reason before, during, and after believing. Even the mysteries of faith are not irrational. On the other hand, Aquinas does not believe that reason alone can bring us to faith in God. This is accomplished only by the grace of God. Indeed, faith can never be based on reason. At best it can only be supported by reason. Thus, reason and evidence are never coercive for faith. There is always room for unbelievers not to believe in God, even though a believer can construct a valid proof that God exists. . . This unique synthesis of faith and reason provides further reasons to believe that old Aquinas should not be forgotten. .
Aquinas and Arguments for God’s Existence
A number of criticisms are raised against Aquinas’ rational demonstration for God’s existence, widely known as his Five Ways. These ways begin with some “effect” that Aquinas considers as evident to us. Generally speaking, Aquinas believed that arguments for God’s existence are in such a way as to argue from effect to cause: particularly, that we can “move from knowledge of an effect to knowledge of God as the cause whose existence must be admitted to account for that effect” . The Five Ways are as follows:
- If there is motion in the creation, there must be a Mover;
- If there are various effects in creation, there must be an Efficient Cause;
- If there is possible existence in the creation, there must be Necessary Existence;
- If there are degrees of perfection in the world, there must be Perfection;
- If there is order in creation, there must be an Intelligent Designer that orders it. 
Of course, there are a couple criticisms that I wish to address which come from Gordon Clark’s book Three Types of Religious Philosophy. In his discussion on Aquinas and his “empirical proofs” for God’s existence, Clark raises several critiques towards his argument(s). Namely, (1) Aquinas’ use of empirical data in an argument for God’s existence is worthless because of David Hume’s attack on natural theology (i.e., Hume was concerned and dealt with empirical arguments, not rationalistic or dogmatic ones); and (2) Aquinas never adequately showed that it was a theistic God he sought out to prove. For instance, where Aquinas says, “And this everyone understands to be God,” Clark uses Karl Barth’s reply that actually very few people understand this to be God:
[I]n particular no Christian understands that Aristotle’s first mover is the God of Abraham, Isaac, and Jacob. It will not do to prove the existence of some kind of first principle. Indeed there is no point in defending the necessity of a first principle of some sort. . . What Christianity needs is the Triune God, and Thomas (though in a sense he tries) cannot pass from the first mover to the Father, Son, and the Holy Ghost. 
The first thing that Clark fails to recognize is what exactly is being excluded in the establishment of Aquinas’ conclusion. For instance, the fact that the Uncaused Cause is not multiple gods – i.e., there can’t be more than one unlimited existence as such – excludes the possibility of polytheism. Furthermore, the Uncaused Cause can’t be interchangeable with the material universe since the universe is a finite, spatiotemporal system – God is unlimited and hence cannot be identical with the space-time universe. Aquinas’ cosmological argument as it stands shows that a theistic God is the best fitting conclusion of this argument (in the theistic sense) .
The initial aspect of Clark’s criticism by using Hume is no longer a valid appeal for rejecting Aquinas’ participation in natural theology. The reason is that, although Hume and his attacks on natural theology were omitting a “Humean aroma” throughout two centuries following his death , academic philosophical research among Christian scholars has been uprising over the last 40 years, as seen in the work of Alvin Plantinga, Richard Swinburne, Nicholas Wolterstorff, William P. Alston, and many others – thus leading to a revaluation of the legitimacy of Hume’s attack on natural theology.
To summarize the entirety of this post, I tried to show that Aquinas contains an apologetic enterprise relevant for all Christian evangelicals to consider. I don’t mean to present this issue as if we are dusting off an old book, but rather that we see the merits of the profound genius of this Angelic Doctor and his contributions to Christian philosophy/theology. There is of course (as I always say) more to address and various ways to approach the subject which I have laid out here, but the key aspects of considering Aquinas a legitimate voice on the matters of faith and reason should ring throughout Christendom with a roar loud enough for unbelievers to hear the rationality associated with religious belief.
-  Bertrand Russell, The History of Western Philosophy (Simon&Schuster: 1972), p. 463
-  Gordon Clark, Three Types of Religious Philosophy (Trinity Foundation: 1983), p. 59
-  Ibid., p. 64
-  Francis Schaeffer, How Should We Then Live? (Crossway Books: 1976), p. 55
-  Francis Schaeffer, The God Who Is There (Inter-Varsity Press: 1968), p. 61
-  Of course, Thomists are not limited to these two groups. For example, Mortimer Adler (Jewish) and Stuart Hackett (Reformed Baptist) shared similar sympathies for Aquinas.
-  G.K. Chesterton, Thomas Aquinas: “The Dumb Ox” (Doubleday: 1956), p. 10
-  Craig Bartholomew and Michael Goheen, Christian Philosophy: A Systematic and Narrative Introduction (Baker Academic: 2013), p. 87.
-  Ibid.
-  Norman Geisler, Thomas Aquinas: An Evangelical Appraisal (Wipf and Stock Publishers: 1991), p. 61.
-  Ibid., p. 62
-  John Hick, Faith and Knowledge: A Modern Introduction to the Problem of Religious Knowledge (Wipf and Stock Publishers: 1966), p. 13.
-  Ibid., pp. 13-14.
-  These 5 points were taken from Norman Geisler (1991), p. 65.
-  Geisler (1991), p. 69.
-  John F. Wippel, “Metaphysics,” Cambridge Companion to Aquinas, ed. Eleonore Stump and Norman Kretzmann (Cambridge University Press: 1997), p. 113.
-  This summary was taken from Bartholomew and Goheen (2013), p. 87.
-  Gordon Clark (1983), p. 64
-  See Geisler (1991), pp. 125-135 for an extended discussion.
-  See In Defense of Natural Theology: A Post-Humean Assessment, ed. James F. Sennett and Douglas Groothuis (Inter-Varsity Press: 2005), pp. 9-10.