Soren Kierkegaard and William James
Both Kierkegaard and James are post-Kantian philosophers of religion. They follow Kant in assuming that humans' capacity for knowledge extends only to the world of the senses (the phenomonal world) — and not to "noumenal" topics like God and souls, which have no empirical foundation. In other words, both Kierkegaard and James assume that human minds lack the necessary capacity to know whether religious claims are true or false: we cannot decide questions of religious belief vs unbelief using our rational faculties.
William James (1842-1910) — American Pragmatist
James' pragmatic argument for faith is as follows:
P1: The choice of belief vs unbelief cannot be decided on the basis of reason.
P2: The choice is living, momentous, and forced.
P3: The practical consequences of suspending judgment (deliberately waiting for rational arguments to appear) are identical to the practical consequences of choosing unbelief.
P4: The practical consequences of choosing belief are usually better than the practical consequences of choosing unbelief.
C: We should choose to believe.
Soren Kierkegaard (1813-1855) — Religious Existentialist
Faith requires that its object be absurd, contradictory, irrational — there can be no reason for it. Faith is by its very nature a leap into the unknown.
If irrationality is a kind of madness, then faith must be a kind of madness.
The story of Abraham illustrates faith as madness. Religious people are usually not perplexed or deeply disturbed by the story of Abraham. They even see Abraham as a role model of faith.
If Abraham is our role model, we should be very afraid, though. Abraham is ready to do something horribly evil, or crazy, because he believes God orders him to.
If Abraham is a real person, he must be morally or intellectually defective to carry out the order.
Abraham must be morally defective if he does not feel horrified and morally repelled. He must be a sociopath or insane.
Abraham must be intellectually defective. I.e., he feels the horror but goes along anyway. He does not think. He does not seem to consider that a good God might not ask this of him. He does not wonder whether the voice telling him to murder his son might be something other than the voice of God: a delusion, a hallucination, the voice of Satan (the great deceiver and tempter), etc. In fact, the last (Satanic) option seems quite reasonable, given that God has promised Abraham that Isaac (his son) will be the leader of a great nation. If God is reasonable and consistent (a logos-type God, as the Judeo-Christian tradition believes) then this rational God, who promised Abraham that Isaac would lead a great nation, would never command Abraham to kill Isaac, thus making it impossible that Isaac become the leader of a great nation. Only Satan would say this, attempting to test Abraham's faith in the real, consistent God. On the supposition that the vision comes from Satan, the right response to the test is for Abraham to ignore the vision and stay faithful to what God has promised him.
Abraham could have chosen to interpret “God”’s voice in a lot of other ways: hallucination, practical joke, etc. Kierkegaard's point is that Abraham chooses to see it with eyes of faith. Faith isn't reasonable and it can't be: if faith were reasonable, then having faith wouldn't require any special effort on the part of the believer. Kierkegaard's point is that real faith requires internal torment: the believer cannot know his religious beliefs are true, because if the believer knew, he wouldn't need faith.
Abraham hears God’s voice only because Abraham decides it is God's voice — and Abraham's decision is arbitrary and irrational and ... well ... it looks kind of crazy, all things considered.
Yet if Abraham is our role model of faith, doesn’t that justify the worst forms of religious fanaticism? Someone like Osama bin Laden also has this kind of arbitrary, irrational, inconsistent faith, no? And yet Kierkegaard thinks that we should make the leap of faith anyway.