Great Christian Thinkers on Faith and Reason

Note: I originally compiled this anthology for christthetao.com.  We considered including it in the upcoming volume, True Reason, which is due to come out in print early in January, but ultimately Tim McGrew and I reworked some of the early sections in more depth for a single chapter.  However, as part of his multi-pronged response to Peter Boghossian's Manual for Creating Atheists, Tom Gilson recently asked if he could post this on his site, Thinking Christian, which he did.  I thought I'd post it here, too, and maybe add new names and quotes as I come across them.  One new one I'll add today is by St. John of Damascus, from the 8th Century.  -- David

The following quotes represent a variety of traditions—Orthodox, Catholic, and Protestant—and vocations—philosophers, theologians, scientists, reformers, and perhaps the greatest Christian missionary after St. Paul: all of them key Christian thinkers speaking on faith and reason—for those who think that faith is disconnected from good thinking.

Justin Martyr 

Reason directs those who are truly pious and philosophical to honour and love only what is true, declining to follow traditional opinions.  (The First Apology):

Justin goes on to give evidence to support his faith, implicitly confirming that faith is backed by evidence.

Clement of Alexandria: Philosophy is “a kind of preparatory training to those who attain to faith through demonstration.” (The Stromata)

Some, who think themselves naturally gifted, do not wish to touch either philosophy or logic; nay more, they do not wish to learn natural science. They demand bare faith alone, as if they wished, without bestowing any care on the vine, straightway to gather clusters from the first . . . 

We must lop, dig, bind, and perform the other operations. The pruning-knife, I should think, and the pick-axe, and the other agricultural implements, are necessary for the culture of the vine, so that it may produce eatable fruit. And as in husbandry, so also in medicine . . . So also here, I call him truly learned who brings everything to bear on the truth; so that, from geometry, and music, and grammar, and philosophy itself, culling what is useful, he guards the faith against assault…. 

Since, therefore, truth is one (for falsehood has ten thousand by-paths); just as the Bacchantes tore asunder the limbs of Pentheus, so the sects both of barbarian and Hellenic philosophy have done with truth, and each vaults as the whole truth the portion which has fallen to its lot. But all, in my opinion, are illuminated by the dawn of Light.

Clement is here referring to Euripides’ play about the King of Thebes. The king having forbidden the worship of Dionysius, the god became angry and drove the women of Thebes mad, till they tore Pentheus to pieces.

The Gospel is therefore a kind of metanarrative, a fuller model that embraces truth found by many methods, among many schools, in many nations. Clement then inventories the moral and scientific discoveries made by various civilizations and philosophers.

Origen, arguing Contra Celsus:

He next proceeds to recommend, that in adopting opinions we should follow reason and a rational guide, since he who assents to opinions without following this course is very liable to be deceived. And he compares inconsiderate believers to Metragytae, and soothsayers, and Mithrae, and Sabbadians, and to anything else that one may fall in with, and to the phantoms of Hecate, or any other demon or demons. For as amongst such persons are frequently to be found wicked men, who, taking advantage of the ignorance of those who are easily deceived, lead them away whither they will, so also, he says, is the case among Christians. And he asserts that certain persons who do not wish either to give or receive a reason for their belief, keep repeating, “Do not examine, but believe!: and “Your faith will save you!”

Origen replies that most people cannot (or will not) devote themselves so exclusively to the pursuit of truth as to prove faith by philosophy. (In those days, of course, most ordinary people were day-laborers, and illiterate.) Should ordinary people enjoy none of the benefits of truth, especially “amelioration of conduct” and the cure of souls, just because they are unable to establish it rationally?

We admit that we teach those men to believe without reasons, who are unable to abandon all other employments ,and give themselves to an examination of arguments; and our opponents, although they do not acknowledge it, yet practically do the same.

But implicitly, Origen seems to admit that for those who have the time, reason (and evidence) must be employed in proving Christian faith. And of course he does employ both; that is the whole point of his book. He admits that historical proof is intrinsically difficult: “the endeavor to show, with regard to almost any history, however true, that it actually occurred, and to produce an intelligent conception regarding it, is one of the most difficult undertakings that can be attempted, and is in some instances an impossibility.” Precociously, seventeen centuries before the historical Troy would be uncovered, Origen gives the Trojan war as an example: “How should we prove that such was the case, especially under the weight of the fiction attached, I know not . . . ”

However, Origen argues that several lines of evidence and argument (including archeology, miracles, history both secular and Christian, and especially prophecy) do support the historical truths of the Gospel.

Irenaeus of Lyon:

Creation itself reveals him that created it; and the work made is suggestive of him that made it; and the world manifests him that arranged it. (Barr, 13)

Basil of Caesarea:

We . . . must first, if the glory of the good is to abide with us indelible for all time, be instructed by these outside means (i.e., reasoning), and then we shall understand the sacred and mystical teachings. (Jarislov Pelikan, Christianity and Classical Culture, 27)

Gregory of Nazianzus: “Faith is what gives fullness to our reasoning.”

Pelikan wrote,

Both ‘faith in search of understanding’ and ‘understanding in search of faith’ had a part in such a method. For even the case of a doctrine that was ‘true already at first sight, as well as credible on the basis of Scripture,’ it was not desirable ‘to leave this part of the subject without philosophical examination,’ because ‘the weakness of the human understanding’ could be ‘strengthened still more by any intelligible rational arguments. (Jaroslav Pelikan, 27-8)

Gregory of Nyssa:

Gregory of Nyssa agreed with that sequence when he said, in reaction to Macrina’s method of theologizing, that is was proper first to propound a doctrine ‘for those trained only in the technical methods of proof’ by means of a ‘mere demonstration, sufficient to convince’ within the limits of reason alone, and only then, because ‘the teachings of the Holy Scripture’ were ‘more trustworthy than any of these artificial conclusions,’ to inquire whether everything that had been proved by reason could also be harmonized with scriptural teachings. (Pelikan, 27)

Tertullian:

The Son of God was crucified: I am not ashamed, because is it shameful. The Son of God died: it is immediately credible, because it is clumsy. He was buried, and rose again: it is certain, because it is impossible.

Along with Martin Luther, Tertullian may be the Christian thinker most often cited to prove the Blind Faith Meme. In A Devil’s Chaplain, Richard Dawkins cites the last line of this quotation, along with the popular, “It is by all means to be believed, because it is absurd.” Dawkins adds, “That way, madness lies.”

But as Alister McGrath explains, Tertullian did not actually write this phantom second quote. What Tertullian is really saying, in the first, is that “The Christian Gospel is profoundly countercultural and counter-intuitive . . . “ He is saying it is not what people would expect, and not what they would have invented. (Dawkins’ God, 100-1)

“Reason is a thing of God, inasmuch as there is nothing which God the Maker of all has not provided, disposed, ordained by reason – nothing which He has not willed should be handled and understood by reason.” (Stark, For the Glory of God, 148, from On Repentance 1)

Habermas also suggested that in the larger context of his views, Tertullian may not have been a fideist. Pratt noted that Tertullian became a heretic, anyway. That so much about Christianity is read from so little from a less than central Christian figure, reveals the lack of warrant for the Blind Faith Meme.

Augustine:

Heaven forbid that God should hate in us that by which he made us superior to the animals! Heaven forbid that we should believe in such a way as not to accept or seek reasons, since we could not even believe if we did not possess rational souls.
In certain matters pertaining to the doctrine of salvation that we cannot yet grasp by reason – though one day we shall be able to do so – faith must precede reason and purify the heart and make it fit to receive and endure the great light of reason . . . for faith to precede reason in certain matters of great moment that cannot yet be grasped, surely the very small portion of reason that persuades us of this must precede faith.” (Stark, 148)

In Concerning Faith in Things Not Seen, Augustine points out that much of our knowledge is in fact based on realities that are not visible to the senses, but are well attested by evidence. He adds, “But they are much deceived, who think that we believe in Christ without any proofs concerning Christ,” and gives a number of pieces of evidence for Christian faith.

The testimony of Augustine is particularly important, since he was probably the most influential Christian thinker outside of the Bible throughout the Middle and early Modern Ages. Here Augustine assumes that faith and reason are complementary, rather than opposed to one another. He also assumes that in most matters, ordinary human reasoning must be used to learn the truth of things. In some matters “relating to salvation” reason is too weak or uninformed to “grasp” the truth, and therefore we rely on faith in revelation. But this step itself is founded on reason. And, of course, Augustine wrote thousands of pages of apologetics that argued from common knowledge to the truth of Christianity.

Habermas commented: “On both Augustine & Anselm, you might want to add/treat their famous statements, ‘I believe in order to understand.’ This has relevance both to their views on faith & reason, but also on their methodology, if belief in some sense precedes reason/understanding.”
“I believe in order to understand” is, indeed, a key phrase for understanding Augustine’s views. Perhaps this should be interpreted in terms of experimental knowledge: “Bite the apple to learn its taste.” In any case, this view does seem to support the mutually affirming relationship between faith and reason.

Kenneth Samples summarizes Augustine’s thoughts on faith and reason, and his use of this phrase, as follows:

In his Sermon (43.7, 9) Augustine asserted: Crede, ut intelligas (‘Believe in order that you may understand’).¹² For Augustine, faith (‘trust in a reliable source’) is an indispensable element in knowledge. One must believe in something in order to know anything. Knowledge begins with faith and faith provides a foundation for knowledge. Faith is itself indirect knowledge (like testimony or authority). While faith comes first in time, knowledge comes first in importance. Faith and reason do not conflict, but instead complement one another. Augustine believed that while reason does not cause faith, reason everywhere supports faith. Augustine also argued that Christians should seek to use their reason to understand doctrines (the Trinity, Incarnation, etc.) that are given via divine revelation (thus ‘faith seeking understanding’). Augustine’s writings about the role of faith influenced Credo, ut intelligam (‘I believe in order that I might understand’) by St. Anselm (a.d. 1033-1109).

In any case, the phrase seems to imply a feedback loop between faith and reason. Reason depends on faith, and then faith also depends on reason. In the abstract, this may sound like circular reasoning. (Of which Pratt seemed to wryly accuse me here, in fact, and others have accused Augustine.)
But life can be like that. You know your mind works, because it works. If it didn’t work, you would never know. Because it does work, to some extent, you can learn more about the mind, logic, and reality, reinforcing and enriching the faith you began with.

When it comes to knowledge, we have to start somewhere. Augustine’s point may be that if we start with faith in God, or reason to it and then start, we will continue to experience a feedback loop of further evidences and richer faith that both depends on that evidence, and discovers more evidence. “Taste and see that the Lord is good.”

St. John of Damascus (The Fount of Knowledge), critiquing Islam (note the importance of sensory experience, prophecy, and eyewitness testimony here):

There are many other extraordinary and quite ridiculous things in this book which he boasts was sent down to him from God. But when we ask: ‘And who is there to testify that God gave him the book? And which of the prophets foretold that such a prophet would rise up?’—they are at a loss. And we remark that Moses received the Law on Mount Sinai, with God appearing in the sight of all the people in cloud, and fire, and darkness, and storm. And we say that all the Prophets from Moses on down foretold the coming of Christ and how Christ God (and incarnate Son of God) was to come and to be crucified and die and rise again, and how He was to be the judge of the living and dead. Then, when we say: ‘How is it that this prophet of yours did not come in the same way, with others bearing witness to him? And how is it that God did not in your presence present this man with the book to which you refer, even as He gave the Law to Moses, with the people looking on and the mountain smoking, so that you, too, might have certainty?’—they answer that God does as He pleases. ‘This,’ we say, ‘We know, but we are asking how the book came down to your prophet.’ Then they reply that the book came down to him while he was asleep. Then we jokingly say to them that, as long as he received the book in his sleep and did not actually sense the operation, then the popular adage applies to him (which runs: You’re spinning me dreams.) [106]

When we ask again: ‘How is it that when he enjoined us in this book of yours not to do anything or receive anything without witnesses, you did not ask him: “First do you show us by witnesses that you are a prophet and that you have come from God, and show us just what Scriptures there are that testify about you”’—they are ashamed and remain silent. [Then we continue:] ‘Although you may not marry a wife without witnesses, or buy, or acquire property; although you neither receive an ass nor possess a beast of burden unwitnessed; and although you do possess both wives and property and asses and so on through witnesses, yet it is only your faith and your scriptures that you hold unsubstantiated by witnesses. For he who handed this down to you has no warranty from any source, nor is there anyone known who testified about him before he came. On the contrary, he received it while he was asleep.

Thomas Aquinas:

It was necessary for man’s salvation that there should be a knowledge revealed by God, besides the philosophical sciences investigated by human reason. First, because man is directed to God as to an end that surpasses the grasp of his reason . . . But the end must first be known by men who are to direct their thoughts and actions to the end. Hence it was necessary for the salvation of man that certain truths which exceed human reason should be made known to him by divine revelation. (Summa Theologica)

At first glance this may seem to support the “faith is not based on reason” camp. But note: there is no suggestion here that reason (or evidence) do not support faith in God, or should not support faith, or that these “certain truths” are illogical or against reason . . . only that they are beyond the discovery of unaided “human” reason. This suggests a supplemental source of knowledge, which I call the fourth level of faith, and show how it is continuous with lower levels. Aquinas goes on to suggest something like that:

We must bear in mind that there are two kinds of science. There are some which proceed from principles known by the natural light of the intellect, such as arithmetic and geometry and the like. There are some which proceed from principles known by the light of a higher science: thus the science of optics proceeds from principles established by geometry, and music from principles established by arithmetic. So it is that sacred doctrine is a science because it proceeds from principles made known by the light of a higher science, namely, the science of God and the blessed.

And how does one establish the authority of the “higher science?” Aquinas explains:

The principles of any science are either in themselves self-evident, or reducible to the knowledge of a higher science; and such, as we have said, are the principles of sacred doctrine . . . Individual facts are not treated in sacred doctrine because it is concerned with them principally; they are rather introduced as examples to be followed in our lives (as in the moral sciences), as well as to establish the authority of those men through whom the divine revelation, on which this sacred scripture or doctrine is based, has come down to us.

So Aquinas assumes that the authority of the authors of Scripture (which he seems to be referring to) should be established, and established by facts.

A page or two later, Aquinas affirms our interpretation of the first passage:

It may well happen that what is in itself the more certain may seem to us the less certain because of the weakness of our intellect, which is dazzled by the clearest objects of nature; as the owl is dazzled by the light of the sun. Hence the fact that some happen to doubt about the articles of faith is not due to the uncertain nature of the truths, but to the weakness of the human intellect . . .

This looks to me like an expression of intellectual humility. Again, bear the explanation of faith I gave in mind in reading the passage that follows:

This science can draw upon the philosophical sciences, not as though it stood in need of them, but only in order to make its teaching clearer. For it accepts its principles, not from the other sciences, but immediately from God, by revelation. Therefore it does not draw upon the other sciences as upon its superiors, but uses them as its inferiors and handmaidens: even so the master sciences make use of subordinate sciences, as political sciences of military science. That it thus uses them is not due to its own defect or insufficiency, but to the defect of our intellect, which is more easily led by what is known through natural reason (from which proceed the other sciences), to that which is above reason, such as are the teachings of this science.

Aquinas may admit that large swaths of Christian doctrine must be accepted on “faith.” This is not, though, because it is irrational, but because God is a surer source of knowledge. Aquinas also flatters reason by taking it to a higher level that it had reached before: to say Aquinas denies the need for reason, would be like saying Leonardo Da Vinci despised oil paints, because he sketched some subjects with a pen.

But he does not include the existence of God in that category:

The existence of God and other like truths about God, which can be known by natural reason, are not articles of faith, but are preambles to the articles; for faith presupposes natural knowledge, even as grace presupposes nature and perfection the perfectible.
From effects not proportioned to the cause no perfect knowledge of that cause can be obtained. Yet from every effect the existence of the cause can be clearly demonstrated, and so we can demonstrate the existence of God from His effects; though from them we cannot know God perfectly as He is in His essence.

Following that, Aquinas gives his famous five “proofs” for the existence God, about which philosophers continue to argue.

Historian Donald Treadgold comments: “Aquinas’ great achievement was to expound the relation between faith and reason in such a way that those who regarded Aristotle as authoritative in philosophy could wholeheartedly remain Christian . . . to build strong intellectual foundations for Christianity and to vindicate the use of reason . . . “ (A History of Christianity, 110)

Treadgold goes on to say, however, that John Scotus and William of Occam stretch Aquinas’ bifurcation between faith and reason to the point of “divorce.”

Pratt added:

“That’s true enough. Not coincidentally, Occam became a deist, abandoning orthodoxy – I’m not sure whether this happened before or after accepting a faith/reason disparity, but I’m sure it was connected with it. (And I still see it happening today.)”

Richard Swinburne explains Aquinas’s masterwork: “The Summa doesn’t start from faith or religious experience or the Bible; it starts from the observable world . . . While I realized that the details were not always satisfactory, it seemed to me that the approach of the Summa was 100 percent right. I came to see that the irrationalist spirit of modern theology was a modern phenomena, a head-in-the-sand defensive mechanism. In general, I believe, it is the spirit of St. Thomas rather than the spirit of Kierkegaard that has been the more prevalent over two millennia of Christian theology.” (Philosophers Who Believe)

John Calvin: reason distinguished man from “true brutes,” and was that “by which man judges between good and evil.”

Chapter in Institutes of the Christian Religion: “Rational proofs to establish the belief of the Scripture.”

Matteo Ricci:

Of all things which mark off all men as being different from animals, none is greater than the intellect. The intellect can distinguish between right and wrong and between that which is true and that which is false, and it is difficult to deceive it with anything which lacks rationality. The stupidity of animals is such that although they possess perception and are capable of motion in much the same way as men, they are incapable of understanding the principles of causality. For this reason their minds are merely concerned with drinking and eating, with mating at appropriate times, and with begetting their own kind. 

Man, then transcends all other creatures since he is endowed with a spiritual soul within, and the ability to observe the principles of things without. By examining the outcome of things he is able to know their origins, and by observing their existence he can know that by which they exist. Thus, without leaving this world of toil, he can devote himself to the cultivation of the Way and prepare himself for an eternity of peace and joy following his death. 

That which is brought to light by the intellect cannot forcibly be made to comply with that which is untrue. Everything which reason shows to be true I must acknowledge as true, and everything which reason shows to be false I must acknowledge as false. Reason stands in relation to a man as the sun to the world, shedding its light everywhere. To abandon principles affirmed by the intellect and to comply with the opinions of others is like shutting out the light of the sun and searching for an object with a lantern.
Now you, Sir, desire to learn the principles of the teachings of the Lord of Heaven. I shall therefore state them plainly for you, and my explanations will be based solely on reason. Should you find any proposition unacceptable I hope you will dispute it and not deceive me in any way. Because we are discussing the universal principles of the Lord of Heaven I cannot permit personal modesty to stand in the way of truth.” (Ricci, The True Meaning of the Lord of Heaven)

This was the most important statement of Christian truth in China since the Nestorian stele in 781. Ricci’s book influenced not only China, but also Vietnam and Korea.

Rene Descartes, writing to “the Dean and Doctors” of the University of Paris:

I have always thought that two questions – that of God and that of the soul – are chief among those that ought to be demonstrated by the aid of philosophy rather than of theology. For although it suffices for believers like ourselves to believe by faith that the soul does not die with the body and that God exists, certainly no unbeliever seems capable of being persuaded of any religion or even any moral virtue, unless these two are first proven to him by natural reason.” (Notes that to believe in God because of Scripture, and in Scriptures because of God, would seem like arguing in a circle.)

Descartes points out (to members of one of the most influential Christian organizations in history, the faculty of the University of Paris) that this is the normal Christian position:

And truly I have noticed that you, along with all other theologians, affirm not only that the existence of God can be proven by natural reason, but also that one may infer from the Holy Scriptures that the knowledge of him is much easier than the manifold knowledge that we have of created things.” (Refers to Romans 1.)

Descartes famously proposes to begin with utter skepticism, and try to prove his own existence, then that of God, from reason alone.
John Locke:

He hath not left himself without witness: since we have sense, perception, and reason, and cannot want a clear proof of him, as long as we carry ourselves about us. Nor can we justly complain of our ignorance in this great point; since he has so plentifully provided us with the means to discover and know him; so far as is necessary to the end of our being, and the great concernment of our happiness. But, though this be the most obvious truth that reason discovers, and though its evidence be (if I mistake not) equal to mathematical certainty: yet it requires thought and attention; and the mind must apply itself to a regular deduction of it from some part of our intuitive knowledge, or else we shall be as uncertain and ignorant of this as of other propositions, which are in themselves capable of clear demonstration.

As for other Christian teachings, Locke, the great peace-maker, proposes to solve the problem of how faith and reason should get along:

I think we may come to lay down the measures and boundaries between faith and reason: the want thereof may possibly have been the cause, if not of great disorders, yet at least of great disputes, and perhaps mistakes in the world. 

Reason, therefore . . . I take to be the discovery of the certainty or probability of such propositions or truths, which the mind arrives at by deduction made from such ideas, which it has got by the use of its natural faculties; viz, by sensation or reflection.
Faith, on the other side, is the assent to any proposition, not thus made out by the deductions of reason, but upon the credit of the proposer, as coming from God, in some extraordinary way of communication. This way of discovering truths to men we call revelation. 

First, then, I say, that no man inspired by God can by any revelation communicate to others any new simple ideas which they had not before from sensation or reflection . . ..
In all things of this kind there is little need or use of revelation, God having furnished us with natural and surer means to arrive at the knowledge of them. “ 

Even original Revelation cannot be admitted against the clear Evidence of Reason . . . But yet nothing, I think, can, under that title, shake or overrule plain knowledge, or rationally prevail with any man to admit it for true, in a direct contradiction to the clear evidence of his own understanding. For, since no evidence of our faculties, by which we receive such revelations, can exceed, if equal, the certainty of our intuitive knowledge, we can never receive for a truth anything that is directly contrary to our clear and distinct knowledge . . . therefore no proposition can be received for divine revelation, or obtain the assent due to all such, if it be contradictory to our clear intuitive knowledge. Because this would be to subvert the principles and foundations of all knowledge . . . In propositions therefore contrary to the clear perception of the agreement or disagreement of any of our ideas, it will be vain to urge them as matters of faith. They cannot move our assent under that or any other title whatsoever.

There is here, it seems, implied admission that higher levels of faith (such as in human testimony) are necessarily weaker than lower levels (in the senses, “physical testimony.” I think this is an over-generalization: sometimes human testimony can provide stronger proof than our own eyes and ears and faulty memory, which is why we ask people, “What was the name of the Laotian girl who sells flowers at the market, again?” But generally speaking, the four steps of faith are like the food pyramid, with each level resting on a lower foundation. The only question is which level God represents – the top, or the base of the pyramid, the ground on which we rest trust in all reason, including that of our minds.

In all things, therefore, where we have clear evidence from our ideas, and those principles of knowledge I have mentioned, reason is the proper judge; and revelation, though it may, in consenting with it, confirm its dictates, yet cannot in such cases invalidate its decrees . . . faith . . . can have no authority against the plain and clear dictates of reason. 

Things above Reason are, when revealed, the proper matter of faith. But, Thirdly, there being many things wherein we have very imperfect notions, or none at all; and other things, of whose past, present, or future existence, by the natural use of our faculties, we can have no knowledge at all; these, as being beyond the discovery of our natural faculties, and above reason, are, when revealed, the proper matter of faith. Thus, that part of the angels rebelled against God, and thereby lost their first happy state: and that the dead shall live again: these and the like, being beyond the discovery of reason, are purely matters of faith, with which reason has directly nothing to do . . . 

Because the mind not being certain of the truth that it does not evidently know, but only yielding to the probability that appears in it, is bound to give up its assent to such a testimony which, it is satisfied, comes from one who cannot err, and will not deceive. But yet, it still belongs to reason to judge of the truth of its being a revelation, and of the significance of the words wherein it is delivered. Indeed, if anything shall be thought revelation which is contrary to the plain principles of reason, and the evident knowledge the mind has of its own clear and distinct ideas; there reason must be hearkened to, as to a matter within its province.

In sum, while Locke’s definitions of faith and reason are in my opinion incomplete, and I would argue against his assumption that what I call lower levels of faith will always be more reliable than what I call the fourth level of faith, Locke agrees that faith in God is established by reason and evidence, our central question. He argues that faith should not be given against reason. And positively, he claims that the sources and meaning of a revelation must be established by what he calls reason.
Blaise Pascal: “

Thought constitutes the greatness of man. Man is but a reed, the most feeble thing in nature; but he is a thinking reed . . . All our dignity consists, then, in thought. . . . Let us endeavor, then, to think well. 

All the principles of skeptics, stoics, atheists, etc. are true. But their conclusions are false, because the opposite principles are also true.” (394)

Pascal’s Wager is only the rhetorical flower on an argument that is full of rational evidence. One chapter is called, Proofs of Jesus Christ. He argues from prophesy and from the unique character of Jesus, among other things.

William Law:

Let truth and plainness, therefore, be the only ornament of your language, and study nothing but how to think of all things as they deserve, to choose everything that is best, to live according to reason and order, and to act in every part of your life in conformity to the will of God . . . As true religion is nothing else but simple nature governed by right reason , so it loves and requires great plainness and simplicity of life.” (A Serious Call to a Devout and Holy Life, Bridge-Logos, 2008, 236)

Law, a kind of chaplain to the Gibbon family before Edward was born and an inspiration to the likes of William Wilberforce and John Wesley, seems to mainly mean by the term “reason” something like “practical wisdom.” He has read the ancient philosophers, and respects them.

Cotton Mather:

Reader, even a Mahometan will shew thee one, without any Teacher, but Reason in a serious View of Nature, led on to the acknowledgment of a glorious God . . . If men so much admire philosophers, because they discover a small part of the wisdom that made all things; they must be stark blind, who do not admire that wisdom itself.” (Mather, Selections, The Christian Philosopher, 291-2)

Mather’s writings are full of observations on Nature and natural philosophy arising from those observations. He is keenly interested in the science of Edmund Halley and Robert Boyle, from which he draws theistic conclusions. (His particularly Christian beliefs are based on other premises.) He is favorable to the theory, an early form of plate tectonics, that Europe and North America were once joined, and were parted by earthquakes, and also to the hypothesis that the Earth is a magnet. (This about 1700!)

John Wesley:

A rational assent to the truth of the Bible is one ingredient in the Christian faith. (Reason for the Hope Within, 136)

Johannes Kepler:

God is supremely rational, and the human being is also rational, being created in the image and likeness of God. Hence religion, which is the expression of the deep relationship between God and humankind, cannot be but rational. (What if the Bible had never been Written, 105)

Here is treated the Book of Nature which is so highly praised by the Holy Scriptures.  Paul presents it to the heathens so that they may see God in it just as the sun can be observed in water or in a mirror. Why should we Christians take less pleasure in contemplating this since it is our task to honor God in the right way, to worship and admire Him?  Our worship is all the more deep, the more clearly we recognize the creation and its greatness . . . “The heavens declare the glory of God . . . “

I do not want to stress that I present important evidence of the creation of the universe — an evidence which has been denied by the philosophers. Nevertheless here we see how God, like a human architect, approached the building of the world according to order and rule and measured everything in such a manner, that one might think not art took  nature for an example but God himself, in the course of his creation took the art of man as an example, though man was only to appear later on.”  (“Dedication to Harbinger of Inquiries concerning the Structure of the Universe and containing the World mystery, Life and Letters, 33-4.)

First Vatican Council (1870): Condemned the idea that inner experience was enough, affirmed that the existence of God could be known with certainty without faith or divine revelation “by the light of human reason.” “In order that our submission of faith be nevertheless in harmony with reason, God willed that exterior proofs of his revelation . . should be joined to the interior helps of the Holy Spirit.” (Barr, 12)

G. K. Chesterton:

A large section of the Intelligentsia seemed wholly devoid of Intelligence . . . It seemed to me that the despised curates were rather more intelligent than anybody else; that they, alone in that world of intellectualism, were trying to use their intellects. (Autobiography, 156-8)

Reason itself is a matter of faith. It is an act of faith to assert that our thoughts have any relation to reality at all . . . There is a thought that stops all thought. That is the ultimate evil against which all religious authority was aimed . . . The creeds and the crusades, the hierarchies and the horrible persecutions were not organized, as is ignorantly said, for the suppression of reason. They were organized for the difficult defense of reason . . . the authority of a man to think . . . And in the act of destroying the idea of Divine authority we have largely destroyed the idea of that human authority by which we do a long-division sum. (Orthodoxy, chapter 3, “The Suicide of Thought.”)

Francis Schaeffer blamed the idea that faith need not be rationally supported on Kant, Hegel, and Kierkegaard:

When he put forth the concept of a leap of faith, he became in a real way the father of all existential thought, both secular and theological. (The God Who is There, 22)

Schaeffer insisted, on the contrary, that Christians should make it clear that “we would be the first ones to step out of the queu” if it should be shown that God is, in fact, NOT there.

C. S. Lewis The most influential modern Christian thinker certainly agreed that faith is based on reason. He said so explicitly in various books (Mere Christianity and Screwtape Letters), in essays, and implicitly by writing several books and articles arguing for the Christian faith.

Have we now got to a position from which we can talk about Faith without being misunderstood? For in general we are shy of speaking plain about Faith as a virtue. It looks so like praising an intention to believe what you want to believe in the face of evidence to the contrary: the American in the old story defined Faith as ‘the power of believing what we know to be untrue.’ Now I define Faith as the power of continuing to believe what we once honestly thought to be true until cogent reasons for honestly changing our minds are brought before us.” (Lewis goes on to point out that most loss of faith is due to non-rational causes, such as a change of environment.) (Religion: Reality or Substitute, from The Seeing Eye, p. 56)

Belief, in (the Christian) sense, seems to me to be assent to a proposition which we think so overwhelmingly probable that there is a psychological exclusion of doubt, though not a logical exclusion of dispute. (Obstinacy of Belief)

Lewis went on to describe the continuity between this “fourth level of faith” (as I call it) and the lower levels:

The scientist himself . . . has beliefs about his wife and friends which he holds, not indeed without evidence, but with more certitude than the evidence, if weighed in the laboratory manner, would justify. Most of my generation had a belief in the reality of the external world and of other people – if you prefer it, a disbelief in solipsism – far in excess of our strongest arguments. It may be true, as they now say, that the whole thing arose from category mistakes and was a pseudo-problem; but then we didn’t know that in the twenties. Yet we managed to disbelieve in solipsism all the same.

Jason Pratt rightly saw a subsequent paragraph as also pertinent:

There is, of course, no question so far of belief without evidence. We must beware of confusion between the way in which a Christian first assents to certain propositions, and the way in which he afterwards adheres to them. These must be carefully distinguished. Of the second it is true, in a sense, to say that Christians do recommend a certain discounting of apparent contrary evidence, and I will later attempt to explain why. But so far as I know it is not expected that a man should assent to those propositions in the first place without evidence or in the teeth of the evidence. At any rate, if anyone expects that, I certainly do not. And in fact, the man who accepts Christianity always thinks he had good evidence; whether, like Dante, [physical and metaphysical argumentation], or historical evidence, or the evidence of religious experience, or authority, or all these together. For of course authority, however we may value it in this or that particular instance, is a kind of evidence.

Pratt also pointed out this passage in Mere Christianity:

I am not asking anyone to accept Christianity if his best reasoning tells him that the weight of the evidence is against it. That is not the point at which Faith comes in. But supposing a man’s reason once decides that the weight of the evidence is for it. I can tell that man what is going to happen to him in the next few weeks. There will come a moment when… all at once his emotions will rise up and carry out a sort of blitz on his belief. [...] I am not talking of moments at which any real new reasons against Christianity turn up. Those have to be faced and that is a different matter. I am talking about moments where a mere mood rises up against it. “Now Faith, in the sense in which I am here using the word, is the art of holding on to things your reason has once accepted, in spite of your changing moods. For moods will change, whatever view your reason takes.

J. P. Moreland (popular evangelical philosopher)

Biblically, faith is a power or skill to act in accordance with the nature of the kingdom of God, a trust in what we have reason to believe is true. Understood in this way, we see that faith is built on reason. We should have good reasons for thinking that Christianity is true before we dedicate ourselves completely to it.

Moreland adds an amusing story, by which he makes the point that evidence had best not be construed to be limited to “physical evidence” tested in the “scientific manner:”

I arrived at the party on time and was at the hors d’oeuvres table when Tom’s boss arrived. Tom brought him over and introduced us to each other. When I extended my hand . . . he started attacking my Christian beliefs without a moment’s hesitation.’
“‘I used to think that religion and philosophy were important, but I now recognize that they are just superstition,’ he asserted. ‘Science is the only area where we have knowledge. If you can quantify something or test it in the lab, then you can know it. Otherwise, it’s just one person’s opinion against another’s. To me, the sole value of religion is that believing it helps some people who need that sort of thing, but religious beliefs are neither true nor rational because they are not scientifically testable.’”
“I let him go on for what seemed like the longest ten minutes of my life. In the most gracious way I could muster, I finally got a chance to respond. ‘I have a few questions for you, Mr. Smith. I am puzzled as to how I should understand what you have asserted for the last ten minutes. You have not said one single sentence from science and nothing you have asserted is the least bit scientifically testable or quantifiable. In fact, you have spent all of your time making philosophical assertions about science and religion. Now, I get the distinct impression that you want me to take your ten-minute monologue as something that is both true and rational. But how can this be, given your scientism, because you do not believe that philosophical assertions are either true or rational? On the other hand, if you don’t think your own assertions are either true or rational, why have you been boring us with emotive expressions of autobiography for the last ten minutes? After all, some of the finger foods are getting cold.” (149)

John Eccles:

Science and religion are very much alike . . . Both are imaginative and creative aspects of the human mind. The appearance of conflict is a result of ignorance. (Christianity on Trial, 84)

Pope John Paul II quoted Declaration on Human Freedom:

Motivated by their dignity, all human beings, inasmuch as they are individuals endowed with reason and free will . . . are bound by both their nature and by moral duty to search for the truth, above all religious truth. And once they come to know it they are bound to adhere to it and to arrange their entire lives according to the demands of such truth. . . The way in which the truth is sought, however, must be in keeping with man’s dignity and his social nature – that is, by seeking freely, with the help of instruction or education, through communication and dialogue . . . ‘

John Paul II then noted:

Man cannot be forced to accept the truth. He can only be drawn to the truth by his own nature . . . This has always been the teaching of the Church. But even before that, it was the teaching that Christ himself exemplified by His actions . . .
“The Council merely reconfirms what has always been the Church’s conviction. The position of Saint Thomas (Aquinas) is, in fact, well known: he is so consistent in his respect for conscious that he maintains that it is wrong for one to make an act of faith in Christ if in one’s conscious one is convinced, however absurdly, that it is wrong to carry out such an act.” Cf Summa Theologiae 1-2, 19.5)” (Pope John Paul II, Crossing the Threshold of Faith)

Richard Swinburne (Oxford U, a leading modern Christian philosopher):

Once I had seen what makes scientific theories meaningful and justified, I saw that any metaphysical theory, such as the Christian theological system, is just a superscientific theory. Scientific theories each seek to explain a certain limited class of data: Kepler’s laws sought to explain the motion of the planets; natural selection seeks to explain the fossil record and various present features of animals and plants. But some scientific theories are on a higher level than others and seek to explain the operation of the lower-level theories and the existence in the first place of the objects with which they deal. Newton’s laws explained why Kepler’s laws operated; chemistry has sought to explain why primitive animals and plants existed in the first place. A metaphysical theory is a highest-level-of-all theory. It seeks to explain why there is a universe at all . . . .
Such a theory is meaningful if it can be stated in ordinary words, stretched a bit in meaning perhaps. And it is justified if it is a simple theory and leads you to expect the observable phenomena when you would not otherwise expect them. Once I had seen this, my program was there – to use the criteria of modern natural science, analyzed with the careful rigor of modern philosophy, to show the meaningfulness and justification of Christian theology.(Philosophers Who Believe)

Mortimer Adler (Jewish philosopher who became a Christian, having published classic books of thought, Encyclopedia Brittanica, etc.): Describes the argument he ultimately found the most persuasive for God’s existence. But then adds:

I therefore concluded by saying that the soundest rational argument for God’s existence could carry us only to the edge of the chasm that separated the philosophical affirmation of God’s existence from the religious belief in God. What is usually called a ‘leap of faith’ is needed to carry anyone across the chasm. But the leap of faith is usually misunderstood as being a progress from having insufficient reasons for affirming God’s existence to a state of greater certitude in that affirmation. That is not the case. The leap of faith consists in going from the conclusion of a merely philosophical theology to a religious belief in a God that has revealed himself as a loving, just and merciful Creator of the cosmos, a God to be loved, worshiped and prayed to.

Consciously following Pascal, Adler affirmed that reason supports Christian faith. Faith, however, transcends reason in the sense that it requires a step into relationship with God that carries other meaning, risks, and rewards than the purely cognitive recognition that the evidence suggests that God is.

John Polkinghorne argues that the cognitive processes involved in Christian faith and scientific discovery are similar:

The ability of understanding to outrun explanation is intimately connected with the religious concept of faith. This is not a polite expression for unsubstantiated assertion, but it points to an ability to grasp things in totality, the occurrence of an insight which is satisfying to the point of being self-authenticating, without dependence on detailed analysis. Involved is a leap of the mind – not into the dark, but into the light. The attainment of understanding in this way does not remove the obligation to seek subsequent explanation, to the degree that it is attainable, but the insight brings with it a tacit assurance that such explanation should be there for the eventual finding. Such experiences are quite common among scientists. Paul Dirac tell us how one of his foundational ideas about quantum theory came to him ‘in a flash’ when he was out for a Sunday walk. He was too cautious to be sure immediately that it was right, and the fact that the libraries were closed prevented his checking it right away. Nevertheless, ‘confidence gradually grew in the course of the night,’ and Monday morning showed that his idea was indeed sound. 

Recognition of the limitations of ratiocination is not indulgence in anti-intellectualism, but rather the avowal that knowledge has a broader base than that afforded by atomized argument alone. (The Faith of a Physicist, 38)

In common with many others, I have wished to revalue the classical ‘proofs’ of God’s existence as suggestive insights rather than logically coercive demonstrations. They are part of those consilient ‘converging lines of probable reasoning’ which constitute a case for theism. (41)

Polkinghorne later reprises Lewis’ (and my) argument about differing modes of argument:

Lewis Wolpert asks the question, ‘Why should religious experience be treated as different from any other experience and not subject to scientific inquiry in the normal way?’ The answer is that all experience is to be subject to rational inquiry, and part of that necessary rationality is to conform one’s investigation to the nature of the entity being investigated. I very much doubt whether Professor Wolpert subjects his enjoyment of music or his encounter with persons ‘to scientific inquiry in the normal way,’ if that phrase is to be interpreted in some flat, universal catch-all, reductionist way.
Religion does not demand that all answers are agreed before the discussion begins. All that it asks for is a respect for its particular modes of experience and an openness to the insights they bestow. (193)

Stephen Barr (physicist):

The believer in religious dogmas accepts that there are two ways that a thing may be known to be true: either empirically, through observation, experience, and the ‘natural light of reason,’ or through divine revelation. Accepting the one does not mean rejecting the other. In fact, in our everyday life we recognize that our knowledge does have a double source: there is what we have learned for ourselves and what we have learned from the information of others, whether teachers, friends, books, or common knowledge. Indeed, a little reflection shows that what we have actually derived from our own direct observation of the world without relying upon the word of others is but a very tiny part of everything that we do know. For a person to accept as knowledge only what he had discovered and proved for himself from direct personal experience would put his knowledge at the level of the Stone Age. 

Taking something on authority, then, is not in itself irrational. On the contrary, it would be irrational never to do so. The question is when we should take something on authority, and on what kind of authority, and how far we should trust it. In the case of religious dogma, the authority is said to be from God, who, it is claimed, has revealed certain truths – primarily truths about himself—to human beings. Such a claim is not in itself contrary to reason, for it is certainly hypothetically possible that there is a God and that he has revealed himself to man. 

On the other hand, reason would require that before accepting religious dogmas we must have some sufficient rational grounds for believing that there is in fact a God, and that he has indeed revealed himself to man, and that this revelation truly is to be found where it is claimed to be found. And, indeed, these requirements of reason have always been admitted by the monotheistic creeds of Judaism and Christianity. (Modern Physics and Ancient Faith, 11-12)