It has been said that he who defines the terms, wins the debate. Skeptics know this and take advantage of it. Witness some of the famous definitions of "faith" provided by unbelievers. Mark Twain, for example, quipped, "Faith is believing what you know ain't so." Closer to our own day, the atheist author Sam Harris defined faith as "the license religious people give themselves to keep believing when reasons fail." Richard Dawkins, perhaps the most famous atheist of our generation, claims: "Faith is the great cop-out, the great excuse to evade the need to think and evaluate evidence. Faith is belief in spite of, even perhaps because of, the lack of evidence."
The one thing all of these definitions have in common is the explicit or implicit idea that faith is in conflict with reason. Unfortunately, some Christians in the history of the church have said things that have provided support for this view of the relationship between faith and reason. Martin Luther, for example, made very strong negative statements about reason, many of which are quoted by skeptics in their attempts to prove that Christianity is inherently irrational. Luther called reason "the Devil's greatest whore." He said in a number of different contexts that reason should be destroyed. The context is crucial, because in these instances Luther was talking about the arbitrariness of unaided human reason to discern divine things. Still, his tendency toward hyperbole has played into the hands of skeptics.
The vast majority of Christians throughout history, however, have not rejected the right use of reason. This stems from their attempt to be faithful to the teaching of Scripture, which itself provides reasons to believe. John wrote his entire Gospel to provide reasons to believe that Jesus is the Christ (John 20:30–31). John, Peter, and Paul appeal to evidence for the claims they make (1 Cor. 15:5–6; 2 Peter 1:16; 1 John 1:1–4). All human beings believe certain things based on the testimony of others. Christians believe what they believe based on the testimony of the Apostles. Such faith is a gift, but it is not divorced from reason.
If we are going to understand better the relationship between faith and reason, we must have a clearer understanding of these two words. The word faith is used in several different ways by Christian thinkers. It can refer to the beliefs that Christians share (the "Christian faith"). The word faith also can refer to our response to God and the promises of the gospel. This is what the Reformed Confessions mean when they speak of "saving faith" (for example, the WCF 14). This faith involves knowledge, assent, and trust. Finally, many philosophers and theologians have spoken of faith as a source of knowledge. As Caleb Miller explains, "The truths of faith are those that can be known or justifiedly believed because of divine revelation, and are justified on the basis of their having been revealed by God."
The word reason also has been used in different ways. It can refer to our human cognitive faculties. The relation of faith to reason in this sense involves asking whether Christian beliefs are reasonable. In other words, did we properly use our cognitive faculties in evaluating these beliefs? We can also use reason to refer to a source of knowledge. In contrast to the "truths of faith" known by divine revelation, the "truths of reason," in this sense, are truths known through natural faculties such as sense perception and memory. A conflict between knowledge derived through natural human faculties and knowledge derived from divine revelation occurs only if an apparent contradiction arises. Finally, in the narrowest sense, reason can be used to refer to logical reasoning. Christians should never argue that there is a conflict here because this faculty is part of who we are as human beings created in the image of God.
Most of the contemporary discussion about the supposed conflict between faith and reason has arisen in the context of discussions about science and religion. Space constraints prohibit a full discussion of this issue, but a few general points should be made in order to help us understand how to think about any alleged conflicts that arise. In the first place, we must acknowledge with Augustine, John Calvin, and many others that all truth is God's truth. That which is true is true because God revealed it, created it, or decreed it.
HE REVEALED IT: All that God reveals, whether through general revelation in His creation or through special revelation in Scripture, is necessarily true. It is impossible for God to lie.
HE CREATED IT: When we learn something about creation that corresponds with what God actually made, we have learned something true. God is the source of these truths by virtue of the fact that He is the Creator.
HE DECREED IT: God is the one who has decreed whatsoever comes to pass. When we learn something about history that is in accordance with what actually happened, we have learned something true to the extent that our knowledge corresponds with what actually happened, and what actually happened only happened, ultimately, because God decreed it.
A second major point that must be made is this: If all truth has its source in God and if all truth is unified, then one thing we know to be certain is that if there is a contradiction between an interpretation of Scripture and an interpretation of what God has created, then one or both of those interpretations is incorrect. They cannot both be correct. Christians must recognize that the conflict may be due to a misinterpretation of creation, to a misinterpretation of Scripture, or to a misinterpretation of both. This means we need to do a thorough and careful examination of both the scientific theory and the biblical exegesis to discover the source of the conflict. We must make sure we are dealing with the actual teaching of Scripture as opposed to a mistaken interpretation of Scripture. And we must examine the evidence for the scientific theory in question to discover whether we are dealing with something that is true about God's creation or something that is merely speculation. All of this hard work takes time, and it means that we do not jump to hasty conclusions.
God created us in His image as rational creatures. Our cognitive faculties were distorted by the fall, but they were not destroyed, and even unbelievers can use these faculties to discover truths about earthly things—as opposed to heavenly things, about which they are completely blind (Calvin, Institutes of the Christian Religion, 2.2.12–21). We do not fully comprehend God, but this is because we are finite and God is infinite. Faith and reason, rightly understood, cannot be and are not in any real conflict.