Broadly speaking, there are three categories of views regarding the relationship between faith and rationality. Rationalism holds that truth should be determined by reason and factual analysis, rather than faith, dogma, or religious teaching. Fideism holds that faith is necessary, and that beliefs must be held without evidence or reason, or even in conflict with evidence and reason. Natural theology holds one can infer, through induction, that God exists by closely observing nature.
From at least the days of the Greek Philosophers, the relationship between faith and reason has been hotly debated. Plato argued that knowledge is simply memory of the eternal. Aristotle set down rules by which knowledge could be discovered by reason.
Rationalists point out that many people hold irrational beliefs, for many reasons. There may be evolutionary causes for irrational beliefs — irrational beliefs may increase our ability to survive and reproduce. Or, according to Pascal's Wager, it may be to our advantage to have faith, because faith may promise infinite rewards, while the rewards of reason are necessarily finite.
Believers in faith — for example those who believe salvation is possible through faith alone — point out that everyone holds beliefs arrived at by faith, not reason. The belief that the universe is a sensible place and that our minds allow us to arrive at correct conclusions about it, is a belief we hold through faith.
Beliefs held "by faith" may be seen existing in a number of relationships to rationality:
Martin Luther taught that faith and reason were antithetical, in the sense that questions of faith could not be illuminated by reason. He wrote, "All the articles of our Christian faith, which God has revealed to us in His Word, are in presence of reason sheerly impossible, absurd, and false. and "[That] Reason in no way contributes to faith. [...] For reason is the greatest enemy that faith has; it never comes to the aid of spiritual things.
René Descartes, for example, argued along these lines in Meditations on First Philosophy, in which he argued that all human perceptions could be an illusion manufactured by an evil demon. Illustrations of this view are also found in contemporary in popular culture, with movies such as The Matrix and Total Recall illustrating the impotence of reason in the face of illusion. Similarly, Theravaada Buddhism holds that all perceived reality is illusion. Thus, it is argued, there is no way to prove beyond doubt that what we perceive is real, so that all our beliefs depend on faith in our senses and memories.
Reformed epistemology asserts that certain beliefs cannot be proven by reason but must be accepted by faith, and Christian philosophers and apologists such as Alvin Plantinga have proposed that beliefs of this type are "properly basic" — that is, that it is right and even necessary to hold such beliefs without evidence. In this view, we believe because we are inclined by nature to believe. Plantinga goes on to argue that belief in God is properly basic in the same way — that belief in God need not come through evidence and argument but may be a "properly basic" belief grounded in natural and intuitive experience.
Presuppositional apologetics claims that faith is a transcendentally necessary precondition to reason. In other words, without faith one could make no sense of reasoning, in terms of the processes or the laws that govern it. It makes the claim that the very concept of "proof" presupposes faith, and thus faith in God is the most rational thing there is.
Solipsism applies reasoning similar to the above to arrive at the conclusion that only the self exists, and all reality is simply a function of one's mind, on the basis that only one's existence can be proven. This view was first recorded with the presocratic sophist Gorgias. Contemporary rationalism has little in common with the historical, continental rationalism expounded by René Descartes and others, which arguably relied on solipsistic reasoning. Plantinga asserts that his argument does not incorporate solipsisms since, while it acknowledges that many things cannot be proven by evidence and reason, it also affirms that things exist outside the mind. Thus, it concludes that faith allows us to "know" things that cannot be strictly proved.
Proponents interpret the following passages of the Bible as teaching this view of faith and reason:
"Now faith is the substance of things hoped for, the evidence of things not seen." Hebrews 11:1
"For now we see through a glass, darkly; but then face to face: now I know in part; but then shall I know even as also I am known." 1st Corinthians 13:12
Some have argued that strict rationalism to the exclusion of this type of faith erroneously concludes that because rational thought is successful at explaining some things, knowledge that comes from beyond the realm of rational thought is illegitimate. According to this line of reasoning,
Our science-dominated culture has ruled out religious experience as a clue to reality; but on what grounds? Science in the 1600’s was so successful in understanding the physical dimension of reality that people in the 1700’s began to think that the physical may be the only dimension of reality. But success in one area of inquiry does not invalidate other areas. The burden of proof is on those who would exclude a particular kind of experience from being a source of knowledge.
Under this view, faith is not static belief divorced from reason and experience, and is not illegitimate as a source of knowledge. On the contrary, belief by faith starts with the things known by reason, and extends to things that are true, although they cannot be understood, and is therefore legitimate insofar as it answers questions that rational thought is incapable of addressing. As such, beliefs held by this form of faith are seen dynamic and changing as one grows in experience and knowledge; until one's "faith" becomes "sight." This sort of belief is commonly found in mysticism.
Rationalists argue that beliefs held by faith, without evidence, contradict one another. Thus most "faiths," in the sense of "religions," hold that their view is correct and that other religions are false religions. The Bible, for examples, says, "Thou shalt have no other Gods before Me." Therefore, of the exclusive religions held through faith, either one is correct and all others are wrong, or they are all wrong. Rationalists argue that if, in all cases but one, faith leads to incorrect belief, then it is wrong in that one case to expect faith to lead to correct belief.
The Anglican C. S. Lewis held that the tenets of Christianity were likely precisely because resurrection from the dead, the miracles and the story of Lazarus seemed to defy rationality. However, he described his experience of faith in his book Mere Christianity by distinguishing between two usages of the word. He describes the first as follows:
Several paragraphs later he continues with:
The 14th Century Jewish philosopher Levi ben Gerson tried to reconcile faith and reason. He wrote, "The Torah cannot prevent us from considering to be true that which our reason urges us to believe. His contemporary Hasdai ben Abraham Crescas argued the contrary view, that reason is weak and faith strong, and that only through faith can we discover the fundamental truth that God is love, that through faith alone can we endure the suffering that is the common lot of God's chosen people.
1. Less semantically precise definitions of rationalism that allow for faith to be accommodated as rational:
The semantic strategy (number 1) is common to those who hold that faith addresses issues beyond the scope of rationality, whereas the epistemological strategy (number 2) is employed by those who hold that faith underlies rationality.
Critics of faith as rational assert that the semantic arguments constitute a special pleading, a formal fallacy. A common refutation of the epistemological attack on the basis of rationality is that if when fully applied it makes it possible to regard any arbitrary belief as rational; one could argue belief in the Invisible Pink Unicorn to be properly basic using the same reasoning. Advocates of Reformed epistemology assert that they have a criterion of proper basic belief; one arrived at inductively. They distinguish between the beliefs and the conditions under which one is believing and correlate the beliefs and the conditions into recognizable groups of those that are properly basic and those that are not properly basic. They argue that as beings we are "naturally inclined" toward belief in God and that because of this condition faith is properly basic and rational, but belief in the Invisible Pink Unicorn or other logical absurdities lack such a condition, are not properly basic and hence not rational. Critics respond to this line of reasoning with though we may indeed be "naturally inclined" toward faith (belief), it does not follow that faith is properly basic and hence rational.
Other people of faith have adopted the position that faith is implicitly irrational and have embraced the putative irrationality of faith as a demonstration of devotion to one's beliefs and deity. For example, Fideism specifically recommends that one not be rational.
W. W. Bartley generalized faith as irrationalism, rationality in this sense as panrationalism, subsumed both under justificationism and criticized and rejected both as authoritarian. He proposed as a new position pancritical rationalism, in which he held that beliefs cannot be based on or justified by anything at all and that rationality only ever concerns the rejection or elimination of views by criticism. He defined a rationalist as someone who keeps all his positions, without exception, and even this rationalist position itself, open to criticism. In this way, Bartley attempted to solve the problem of the tu quoque attack used by fideists on rationalists. This attack argues that if a belief is to be based on reason or evidence, it must at one point also make use of faith, for otherwise it would face infinite regress. The attack not only undermined the integrity of the rationalist, because it exposed him as ultimately relying on faith and hence being actually irrational, but it at the same time gave the fideist a justification for his faith and so held his view to be as rational as the rationalist's view, according to the rationalist's own standards.