Cogito ergo deus est: I think therefore God exists. Philosophy and history both show that atheists have no reason to trust reason, and that people who believe in reason should also believe in God. Philosophy shows that thoughts coming from chemical reactions are not to be trusted, but naturalism says all thoughts come from chemical reactions. From the sophists two hundred years before Christ to Stephen Hawking today, people who do not believe in God show, by the arguments they make and the way they argue, that they do not trust reason. On the other hand, people who do trust reason, from Socrates to John Lennox, link its reliability with its origin in God. They are right to do so, because the best explanation of reason’s effectiveness is that it comes from a reasonable God.
David Hume probably never told this joke, but it illustrates a central tenant of his philosophy: Two men are riding on a train from London to Edinburgh. One of the men is reading a book, and after he finishes each page, he rips it from the volume and casts it out the window. After observing this action for a few minutes the other man inquires, “Sir, why are you throwing book pages out of the train window?” “Why,” the first man replies, “obviously to keep the elephants off the tracks. If we should collide with an elephant a great loss of life could result.” “But, sir,” cried the second man, “there are no elephants on the tracks!” To which the first man responds, “Effective, isn’t it?”
What makes this joke funny is that the first man thinks his throwing the torn pages from the train is what keeps elephants off the tracks, when the real reason is that elephants do not roam loose through Great Britain. Hume would never make such a mistake about cause and effect because he denied that there is any sure way to reason about causes and effects. He also denied that we have any direct knowledge of the external world, and that we should trust that the future will be like the past. This denial of cause and effect, of objective reality, and of the continuity of nature amounted to a clear rejection of the use of reason as a reliable guide to truth.
Hume’s skepticism about reason reveals a fatal weakness in an atheist’s armor and puts a sharp sword in the hand of the Christian apologist. Atheists can give no reason why they should value reason, and Christians can show how anyone who believes in reason must also believe in God.
The problem for atheists is that they deny the supernatural world. For them, in the words of Carl Sagan, the cosmos, with its energy, matter, time, and space, “is all that is, or ever was, or ever will be.” In this naturalistic world, ideas are mere epiphenomena, a surface appearance caused by something real, like the apparent pictures caused by the real pixels on a TV screen. When we think, the atoms in our brain move, causing the thoughts. The atoms are the cause and the thoughts are merely the effect. Thus Bertrand Russell avers that all human beliefs are but “accidental collocations of atoms.” The atoms in our brain happen to move about in a certain way, and thus we think various thoughts.
We know that the atheists are partly right: some thoughts do have chemical causes. LSD and other drugs can produce sensations, perceptions, and thoughts in our brains that have no relation to the outside world. From this limited experience and from their naturalistic worldview, atheists leap to the conclusion that all thoughts are physically caused. But thoughts that are physically caused are not caused by reason. Thus they are non-rational by definition. And we are rightly suspicious of non-rational thoughts. No one trusts the drug-induced ravings of a friend on a psychedelic trip. Indeed, we protect them from the illusions that they can fly or deflect bullets.
The problem for atheists is that having strapped on the skis of physically-caused thought, they cannot stop anywhere on the mountain of rationality, but must descend into the valley of non-rationalism. If there is no criterion of rationality, how does one evaluate one’s thoughts? When John Nash, whose story is told in A Beautiful Mind, was overcome by phobias and obsessions, he thought his way back to health by rational therapy. He tested each thought by the outside standard of reason and decided which thoughts to trust and which to dismiss. Atheists, however, have nothing outside. Even the real world, which they admit really is outside their brains, comes into their minds only through perceptions. These perceptions, they have to believe, are caused by physical changes in their brains.
Since atheists believe that the cosmos is all there is, and since reason is not made up of energy, matter, time, space, atheists have no valid reason to believe in reason. How ironic when so many atheists call themselves “Brights” that they have no ability to shine the light of reason on to their thoughts.
The idea that without God there is no reason to trust reason has an ancient pedigree. The first thinkers to realize the impotence of reason without a God to empower it were the Greek skeptics who doubted the ability of logic to lead to truth. A hundred years after Socrates, Plato, and Aristotle had based their philosophies on inerrant reason, the Sophists arose and claimed they could teach anyone to use logic convincingly to argue any point. They believed that for every conceivable argument an equal and opposite argument could be offered. Illustrating their point, an orator named Carneades in Rome gave equally persuasive speeches for and against justice on successive days in 155 B.C. A second attack on atheistic reason came from the Muslim Al-Ghazali, whose book, The Destruction of the Philosophers, argued from optical illusions that we cannot trust our senses and from logical paradoxes that we cannot trust reason. David Hume’s attack in the eighteenth century roused Kant from his dogmatic slumbers, but instead of a refutation, he only produced further critiques, one of practical reason and the other of pure. After Kant, Charles Darwin realized that his brain taught him that it and a monkey’s brain shared a common ancestor, but then ironically asked, “… would anyone trust in the convictions of a monkey’s mind …?” Shortly after Darwin, Arthur Balfour, a thinker who later became Prime Minster of Great Britain, pointed out that since empirical science can give only a non-rational source for human beliefs, such science must be supplemented by a belief in God if human thinking is to have any validity. Noted atheist biologist J. B. S. Haldane realized that “if my mental processes are determined wholly by the motions of atoms in my brain I have no reason to suppose that my beliefs are true.” In order to escape what he called sawing off the branch on which he sat, he felt compelled to believe in something like a mind which exists behind nature.
In our time C. S. Lewis highlighted the fatal self-contradiction of naturalism showing that a materialist view of the universe leaves no place for rational thought. Thus naturalism is autophagus, devouring itself, much like the Unitarian bumpersticker which imperiously orders us to “Question Authority.” Alvin Plantinga has offered the self-contradiction of naturalism as a defeater of belief in evolution by natural selection, demonstrating that if we start with the presumption that such evolution is true, we will then believe that everything about ourselves, including our belief in Darwinian evolution, can be accounted for in terms of sexual selection, a profoundly non-rational process. Thus true believers in the neo-Darwinian evolutionary synthesis must acknowledge that their belief is not rational, that they have no rational reason to trust their minds to believe that evolution (or anything else for that matter) is true. Cosmologist Paul Davies makes the same point of the inability of naturalism to account for rational thought, showing that evolution explains why our minds allow us to avoid dangers and to find mates, but then arguing that natural selection cannot account for our rational human minds with their ability to understand everything from atoms to black holes. Davies has been backed up by atheist philosopher Thomas Nagel who calls the evolutionary explanation of human reason “laughably inadequate.”
Philosophy and science
Recently Stephen Hawking, the man who holds Isaac Newton’s chair at Trinity College, Cambridge, published a book, The Grand Design, which he thinks will explain everything without the hypothesis of God. On the opening page he says, “Philosophy is dead,” meaning that speculation about the universe is pointless, and only “science” will lead to truth. Hawking seems to forget that trying to do science without philosophy is like trying to do language without grammar. Philosophy is not so much a separate branch of investigation, but the rational way we conduct all investigation. He uses the alleged death of philosophy as a cover for absurd statements, such as “Because there is a law like gravity, the universe can and will create itself from nothing….” Hawking apparently does not notice that gravity is not an independent entity which can do things on its own, but only a personification of the tendency of masses to attract each other. Nor does he realize that when he posits gravity as the creator he gives no account for its origin, nor the recognition that without mass there is no gravity. Hawking’s unconscious irrationality, like the conscious rebellions of earlier thinkers against rationality, is just the latest instance of how abandoning God leads the atheist to abandon reason.
Not only does thinking about reason reveal a fatal weakness in an atheist’s armor, it also puts a sharp sword in the hand of the Christian apologist. In order to maintain one’s trust in reason, one must come to trust in God. Belief in reason frees the mind from its naturalistic prison, and allows entrance into a world containing spiritual realities. Once reason gets its spiritual foot in the door, the entry of God cannot be far behind.
The argument from reason to God is not one of deduction, or induction, but of abduction, or inference to the best explanation. Given that any situation can be explained in an infinity of ways, which explanation best accounts for the situation? Abductive reasoning is the key to the situational riddles kids love: You enter a room and see Billy and Sally lying dead on the floor surrounded by water and broken glass. They bear no wounds on their bodies and they have not been poisoned. What happened? Out of numberless possible explanations, the answer is that someone knocked over their bowl and broke it. Billy and Sally are goldfish.
Grasping human reason
Given the human ability to reason correctly, what is the best explanation for this phenomenon? Either human reason comes from a naturalistic, non-rational cause or it comes from an immaterial, rational cause. More than twenty centuries of thought have shown that non-rational, physical forces cannot give rise to rationality: matter can never even give rise to mind, much less to rationality. Thus human reason must rise from a rational source. Besides the physical universe, then, there must be a non-human rational mind, and this mind must be the source of human rationality. This human rationality enables people rightly to reason—to evaluate their thoughts and see which ones are logical and coherent. It is not a product of one’s mind, but comes from outside and enables one to control the mind. In addition to adjudicating between human thoughts, this rationality also empowers people to understand the created order, the cosmos so beloved by Carl Sagan. How ironic that his favorite word for the universe was cosmos, which comes from the Greek word meaning beauty and bespeaks its order and intelligibility. Not only inside the human mind does reason rule, but outside their heads it seems to have imposed its laws upon the created order. Because reason reigns both in the physical universe and in the consciousness, humans can comprehend both worlds. They can order their thoughts and understand the cosmos. When thinkers realize that a trust in reason leads them to a non-human, immaterial Mind who also stamped its mark on the universe, they soon discover that they believe in God.
The idea that reason exists independent of humans and that it shapes the world began with the Greeks. Six centuries before Christ, Heraclitus said there was a logos, a word or reason, by which the world was created. The men against whom the Sophists rebelled, Socrates, Plato, and Aristotle, all believed in the logos and the spiritual reality which it and God inhabited.  Around the time of Jesus, Philo said that this logos was God’s creative principle, and John’s gospel identifies the logos with God the Son who created everything. So Greeks, Jews, and Christians have long linked our human ability to reason with God’s existence, as well as his creativity and our ability to understand the world.
When Descartes created modern philosophy by questioning everything he did not know directly, he eventually reasoned that God must exist. Cogito, ergo sum began a process that finally convinced him that there was a God. His train of reasoning was long and involved, but recently Oxford mathematician John Lennox, in a response to Hawking’s book, has, like Anselm before him, been able to telescope this complicated argument into a simple deduction: Cogito ergo deus est, I think therefore God exists. Einstein marveled that the most incomprehensible fact about the universe was the fact that it was comprehensible. Lennox explains why it is so: both the universe and the human mind come from the logos. And the logos is God. QED: cogito ergo deus est.
So Christians have a sharp, two-edged sword. They can ask atheists why they trust in reason, and then show them that without God such a reliance is blind faith. Then they can show them that the best inference for the existence of reason and for the intelligibility of the universe is the God of the Bible. “In the beginning there was logic” (John 1:1).
Dr. Charles (Chuck) White teaches courses on Christian thought and history at Spring Arbor University. He has studied at Harvard, Gordon-Conwell, Cambridge, and Boston. His undergraduate degree is in history and literature, and his doctorate is in church history. He began his professional career as minister to students in Boston’s historic Park Street Church, and has taught in Australia, Nigeria, and the Philippines. He has published two books, nine scholarly articles, and a score of popular essays. Outside the classroom he helped to start a crisis pregnancy center and raises money to support Bible Women in India. His research interests are John and Charles Wesley, 19th century American Methodism, and the doctrine of Scripture.
 David Hume, An Enquiry into Human Understanding, second edition (London: A. Millar, 1750) sections 4, 7, and 12. See An Enquiry into Human Understanding and other Essays, edited by Ernest C. Mossner (New York: Washington Square Press, 1963), 36-49, 69-83, 146.
 This essay assumes that an atheist is also a naturalist. There may be some Platonic atheists or other atheistic idealists who believe in the Forms or other spiritual realities, but they are so few that most readers will not encounter them. Sagan expresses his faith in the first sentence of the Cosmos series.
 Bertrand Russell, “A Free Man’s Worship,” is widely available on the web. For a scholarly edition with some documentation, see Volume 12 of The Collected Papers of Bertrand Russell, entitled Contemplation and Action, 1902-14 (London, 1985; now published by Routledge).
 Sylvia Nasar, A Beautiful Mind (New York: Simon & Schuster, 1998).
 Raoul Mortley, From Word to Silence (Bonn: Peter Hanstein Verlag GmbH, 1986), 34.
 Kojiro Nakamura, “Al-Ghazali, Abu Hamid (1058-1111),” available at www.ghalazi.org.
Charles Darwin to W. Graham, July 3, 1881, in The Life and Letters of Charles Darwin, ed. Francis Darwin (1897; repr., Boston: Elibron, 2005), 1:285.
 Arthur James Balfour, The Foundations of Belief, 8th ed. (New York: Longmans, Green & Co., 1902).
 J. B. S. Haldane, “When I Am Dead” in Possible Worlds (London: Chatto & Windus, 1927; reprint New Brunswick, NJ: Transaction Publishers, 2002), 209-10.
 C. S. Lewis, Miracles (New York: Collier Books, 1960), 15. Victor Reppert defends and expands Lewis’s argument in his masterful C. S. Lewis’s Dangerous Idea: In defense of the argument from reason (Downers Grove, IL: Intervarsity Press, 2003).
 Alvin Plantinga, Where the Conflict Really Lies: Science, Religion, and Naturalism (New York: Oxford University Press. 2011).
 Paul Davies in The Privileged Planet: the search for purpose in the universe (Murrita, CA: Illustra Media, 2004).
 The phrase comes from Thomas Nagel, The Last Word (New York: Oxford University Press, 1997), 75. He explains his idea more fully in The View from Nowhere (New York: Oxford University Press, 1986), 78-81.
 Steve Hawking, The Grand Design (New York: Bantam Books, 2010), 5.
 Hawking, 180.
 Charles H. Khan, The Art and Thought of Heraclitus (Cambridge: Cambridge University Press, 1979).
 Mortley, 19-30.
 Philo, Legum Allegoriarum 3:96 . See The Works of Philo, translated by C. D. Yonge, edited by David M. Scholar (Peabody, MA: Hendrickson Publishers, 2013).
 René Descartes, Meditations on the First Philosophy, translated by Elizabeth S. Haldane and G. R. T. Ross (Franklin Center, PA: The Franklin Library, 1981), 133-208.
 Anselm of Canterbury, “Preface to Proslogion” in Anselm of Canterbury, vol. 1, edited by Jasper Hopkins and Herbert Richardson (New York: The Edward Mellon Press, 1975), 89, and John Lennox, God and Stephen Hawking: Whose Design Is It Anyway? (Oxford: Lion, 2011), 73-95.
 Albert Einstein, “Physics and Reality”(1936), in Ideas and Opinions, trans. Sonja Bargmann (New York: Bonanza, 1954), 292.