Is it ever rational to believe something for which one has insufficient evidence? If it is never rational to believe something for which one has insufficient evidence, then presumably it is also never rational to act upon such a belief. For example, if it irrational to believe in God and post-mortem survival, then presumably it is also irrational to act upon those beliefs, by entering a monastery, say. Or is it?
W. K. Clifford is famous for his evidentialist thesis that "It is wrong always, everywhere, and for anyone, to believe anything on insufficient evidence." On this way of thinking, someone who fails to apportion belief to evidence violates the ethics of belief, and thereby does something morally wrong. This has been called ethical evidentialism since that claim is that it is morally impermissible to believe on insufficient evidence. Sufficient evidence is where there is preponderance of evidence. On ethical evidentialism, then, it is morally permissible for a person to believe that p if and only p is more likely than not on the evidence the person has.
A cognitive evidentialist, by contrast, maintains that one is merely unreasonable to believe beyond a preponderance of evidence. One then flouts a norm of rationality rather than a norm of morality.
Jeffrey Jordan, who has done good work on this topic, makes a further distinction between absolute and defeasible evidentialism. The absolute evidentialist holds that the evidentialist imperative applies to every proposition, while the defeasible evidentialist allows exceptions. Although Clifford had religious beliefs in his sights, his thesis, by its very wording, applies to every sort of belief, including political beliefs and the belief expressed in the Clifford sentence quoted above! I take this as a refutation of Clifford's evidentialist stringency. For if one makes no exceptions concerning the application of the evidentialist imperative, then it applies also to "It is wrong always, everywhere, and for anyone, to believe anything on insufficient evidence." And then the embarrassing question arises as to what evidence once could have for the draconian Cliffordian stricture which is not only a morally normative claim but is also crammed with universal quantifiers.
If I took Clifford seriously I would have to give up most of my beliefs about politics, health, nutrition, economics, history and plenty of other things. For example, I believe it is a wise course to restrict my eating of eggs to three per week due to their high cholesterol content. And that's what I do. Do I have sufficent evidence for this belief? Not at all. I certainly don't have evidence that entails the belief in question. What evidence I have makes it somewhat probable. But more probable than not? Not clear! But to be on the safe side I restrict my intake of high-cholesterol foods. What I give up, namely, the pleasures of bacon and eggs for breakfast every morning, etc. is paltry in comparison to the possible pay-off, namely living and blogging to a ripe old age. Surely there is nothing immoral or irrational in my behavior even though I am flouting Clifford's rule. And similarly in hundreds of cases.
The Desert Rat
Consider now the case of a man dying of thirst in a desert. He comes upon two water sources. He knows (never mind how) that one is potable while the other is poisonous. But he does not know which is which, and he has no way of finding out. Should the man suspend belief, even unto death, since he has insufficient evidence for deciding between the two water sources? Let us suppose that our man is a philosopher and thus committed to a life of the highest rationality.
Absolute evidentialism implies that the desert wanderer should suspend judgment and withhold assent: he may neither believe nor disbelieve of either source that it is potable or poisonous on pain of either irrationality or an offence against the ethics of belief.
On one way of looking at the matter, suspension of belief -- and doing nothing in consequence -- would clearly be the height of irrationality in a case like this. The desert wanderer must simply drink from one of the sources and hope for the best. Clearly, by drinking from one (but not both) of the sources, his chances of survival are one half, while his chances of survival from drinking from neither are precisely zero. By simply opting for one, he maximizes his chances of reality-contact, and thereby his chances of survival. Surely a man who wants to live is irrational if he fails to perform a simple action that will give him a 50-50 chance of living when the alternative is certain death.
He may be epistemically irrational, but he is prudentially rational. And in a case like this prudential rationality trumps the other kind.
Cases like this are clear counterexamples to evidentialist theories of rationality according to which rationality requires always apportioning belief to evidence and never believing on insufficient evidence. In the above case the evidence is the same for either belief and yet it would be irrational to suspend belief. Therefore, rationality for an embodied human agent (as opposed to rationality for a disembodied transcendental spectator) cannot require the apportioning of belief to evidence in all cases, as Clifford demands. There are situations in which one must decide what to believe on grounds other than the evidential. Will I believe that source A is potable? Or will I believe that source B is potable? In Jamesian terms the option is live, forced, and momentous. (It is not like the question whether the number of ultimate particles in the universe is odd or even, which is neither live, forced, nor momentous.) An adequate theory of rationality, it would seem, must allow for believing beyond the evidence. It must return the verdict that in some cases, to refuse to believe beyond the evidence is positively irrational.
But then absolute evidentialism is untenable and we must retreat to defeasible evidentialism.
The New Neighbors
Let us consider another such case. What evidence do I have that my new neighbors are decent people? Since they have just moved in, my evidence base is exiguous indeed and far from sufficient to establish that they are decent people. (Assume that some precisifying definition of 'decent' is on the table.) Should I suspend judgment and behave in a cold, skeptical, stand-offish way toward them? ("Prove that you are not a scumbag, and then I'll talk to you.") Should I demand of them 'credentials' and letters of recommendation before having anything to do with them? Either of these approaches would be irrational. A rational being wants good relations with those with whom he must live in close proximity. Wanting good relations, he must choose means that are conducive to that end. Knowing something about human nature, he knows that 'giving the benefit of the doubt' is the wise course when it comes to establishing relations with other people. If you begin by impugning the integrity of the other guy, he won't like you. One must assume the best about others at the outset and adjust downwards only later and on the basis of evidence to the contrary. But note that my initial belief that my neighbors are decent people -- a belief that I must have if I am to act neighborly toward them -- is not warranted by anything that could be called sufficient evidence. Holding that belief, I believe way beyond the evidence. And yet that is the rational course.
So again we see that in some cases, to refuse to believe beyond the evidence is positively irrational. A theory of rationality adequate for the kind of beings we are cannot require that belief be always and everywhere apportioned to evidence.
In the cases just mentioned, one is waranted in believing beyond the evidence, but there are also cases in which one is warranted in believing against the evidence. In most cases, if the available evidence supports that p, then one ought to believe that p. But consider Jeff Jordan's case of
The Alpine Hiker
An avalanche has him stranded on a mountainside facing a chasm. He cannot return the way he came, but if he stays where he is he dies of exposure. His only hope is to jump the chasm. The preponderance of evidence is that this is impossible: he has no epistemic reason to think that he can make the jump. But our hiker knows that what one can do is in part determined by what one believes one can do, that "exertion generally follows belief," as Jordan puts it. If the hiker can bring himself to believe that he can make the jump, then he increases his chances of making it. "The point of the Alpine hiker case is that pragmatic belief-formation is sometimes both morally and intellectually permissible."
We should therefore reject absolute evidentialism, both ethical and cognitive. We should admit that there are cases in which epistemic considerations are reasonably defeated by prudential considerations.
And now we come to the Big Questions. Should I believe that I am libertarianly free? That it matters how I live? That something is at stake in life? That I will in some way or other be held accountable after death for what I do and leave undone here below? That God exists? That I am more than a transient bag of chemical reactions? That a Higher Life is possible?
Not only do I not have evidence that entails answers to any of these questions, I probably do not have evidence that makes a given answer more probable than not. Let us assume that it is not more probable than not that God exists and that I (in consequence) have a higher destiny in communion with God.
But here's the thing. I have to believe that I have a higher destiny if I am to act so as to attain it. It is like the situation with the new neighbors. I have to believe that they are decent people if I am to act in such a way as to establish good relations with them. Believing the best of them, even on little or no evidence, is pragmatically useful and prudentially rational. I have to believe beyond the evidence. Similarly in the Alpine Hiker case. He has to believe that he can make the jump if he is to have any chance of making it. So even though it is epistemically irrational for him to believe he can make it on the basis of the available evidence, it is prudentially rational for him to bring himself to believe. You could say that the leap of faith raises the probability of the leap of chasm.
And what if he is wrong? Then he dies. But if he sits down in the snow in despair he also dies, and more slowly. By believing beyond the evidence he lives better his last moments than he would have by giving up.
Here we have a pragmatic argument that is not truth-sensitive: it doesn't matter whether he will fail or succeed in the jump. Either way, he lives better here and now if he believes he can cross the chasm to safety. And this, even though the belief is not supported by the evidence.
It is the same with God and the soul. The pragmatic argument in favor of them is truth-insensitive: whether or not it is a good argument is independent of whether or not God and the soul are real. For suppose I'm wrong. I live my life under the aegis of God, freedom, and immortality, but then one day I die and become nothing. I was just a bag of chemicals after all. It was all just a big joke. Electrochemistry played me for a fool. So what? What did I lose by being a believer? Nothing of any value. Indeed, I have gained value since studies show that believers tend to be happier people. But if I am right, then I have done what is necessary to enter into my higher destiny. Either way I am better off than without the belief in God and the soul. If I am not better off in this life and the next, then I am better off in this life alone.
I am either right or wrong about God and the soul. If I am right, and I live my beliefs, then then I have lived in a way that not only makes me happier here and now, but also fits me for my higher destiny. If I am wrong, then I am simply happier here and now.
So how can I lose? Even if they are illusions, believing in God and the soul incurs no costs and disbelieving brings no benefits.