I. Blaise Pascal (1623-1662): According to Pascal's Wager , we ought to believe in the existence of God because it is the prudent thing to do. Since belief in an absolutely perfect being cannot be proven or rationally justified, it boils down to whether there is more reason to believe in God than not to believe in God. After all, either God exists or he doesn't. That is, the probability of God's existence is 50-50. What you have to consider are not only the odds of God's existing but also the benefits or losses of making the commitment to believe.
There are four possible scenarios here. If you believe in God and he exists, then you have made a finite effort (going to church, living according to the laws of God) and stand to get an infinite reward. If you believe in God and he doesn't exist, you haven't lost much (maybe you don't party as much as you may have). If you don't believe in God and he exists, you run the risk of eternal damnation. And if you don't believe in God and he doesn't exist, then you have a finite life of wicked enjoyment and you luck out by not having to pay for it in an afterlife. Given those odds and the potential rewards, Pascal says it would be reasonable to believe.
Objections :
(1) This reduces religious belief to simply going with the odds, hedging one's bets; and that does not seem worthy of true religious commitment.
Reply: God rewards belief, regardless of how the believer comes to it.
(2) Given the evil we experience in the world and all the arguments that can be raised against the existence of God, the probability of his existence is much less than 50-50. We could be wrong in believing in God, thus missing the opportunity to enjoy the wicked pleasures of life, and even (in certain rare instances) risking our lives?
Reply: even if the odds are very small that God exists, the payoff is infinite. So why not believe, even if we don't have convincing evidence or run risks?
II. William James (1842-1910): Belief in the existence of God is something that the intellect cannot decide. But because such a belief can make a major difference in how one lives, a choice (or volition) must be made, one that because of the situation would be a justified (i.e., meaningful) decision. The belief in God's existence "works" (and thus is true) if it satisfies our expectations and is consistent with other beliefs. The question about whether there is a God, then, is not really the issue; what is more important is whether one should believe that God exists, and that choice is determined as justified based on what kind of life would follow from having made such a commitment. The believer will think that his or her life has a purpose, meaning, and outcome that the non-believer will not experience. And that is significant enought for James to be the basis for deciding in regard to situations in which there are no intellectual grounds for deciding one way or the other.
Objection : Just because something is consistent with our other beliefs, that does not necessarily mean that it is true. And besides, if it really works, it is because it is true. So what we should be looking for is not whether a belief satisfies our expectations or gives our lives meaning; we should be trying to determine whether it is true and justified apart from its impact of our lives.
III. Soren Kierkegaard (1813-1855): Religious beliefs are, after all, beliefs, not objective bits of knowledge. Our anguish (angst ) over, the ambiguity of human existence--what is its point if we are going to die anyway?--raises the prospect of the meaninglessness of our existence. Since no convincing arguments can be given to justify existence itself, the only proper (i.e., authentic) response is unconditioned faith , belief that there is a God who has promised us his salvation.
The three enemies of authentic existence and faith are: (1) established Christianity (i.e., doing what the Church says is right); (2) middle-class, bourgeois culture (i.e., doing what society says is right); and (3) the dominant philosophy of the day (i.e., Hegelianism, a philosophy in which truth is described as objective, rational, totalizing). Some people (those who adopt what Kierkegaard calls the aesthetic life) will do simply what "feels" right according to society because it is what we have been taught. Others (acting in accord with the moral life) do what can be rationally justified (philosophically). But only the religious life is truly authentic. That is, only acting on faith that one's particular actions are right (even if they contradict what society or reason says) is truly religious.
This means that religious truth (and, in fact, all truth ultimately) is subjective. Rationality and knowledge are based on the premise that truth is objective, impersonal, a relationship between a belief and the world. But the truth about human existence is not something about which we are simply intellectually curious; it is rather something about which we care deeply. Our caring about it determines it as something different from other things; that is, what it is becomes a function of how we feel about it. Our existence and salvation are meaningful not because they correspond to some objective fact; meaning is a function of the character of unconditioned, passionate belief without the guarantee of escape from inner reservations or doubt.
This means that authentic existence requires from us a leap of faith. There is thus ultimately no justification for the belief in eternal life and God's existence, and the gap between the finiteness of our comprehension and the infinity of the justification is incommensurable (lacking all means for comparing the two). Only a leap of faith can surmount the gap. Religious belief must be just that--a belief for which one cannot give rational justification. Knowledge of moral directives is rationally possible on a universal level but not on the personal level, and doing something because it is the socially acceptable (or aesthetic) thing to do involves no faith at all. Moral knowledge is general, faith in salvation is particular. The leap of faith is not irrational as much as beyond rationality.
Abraham in the Old Testament is a classic example of the person of faith. For Kierkegaard, he is the embodiment of the religious mentality. Abraham is not great because he is willing to sacrifice what he loves most (his son, Isaac); he is great because he acts not knowing (in fear and trembling) whether he is right but nonetheless believes that this is what God asks of him. Humanly speaking, he is insane because his act is unintelligible and even contradicts what God has told him to expect as the father of a great nation: he acts "by virtue of the absurd." By taking responsibility for one's actions and affirming one's power, the authentic individual exhibits the kind of faith and commitment that provides no guarantees or proofs. In the end, religious belief thus boils down to an attitude that is unjustifiable.
Objection : The problem with all this is that does not allow us to distinguish the true person of faith from someone who is mad or a fanatic. Religion and insanity are thus indiscernible.