Thomas Nagel on "A Priori" Belief

A reader draws my attention to this essay by NYU professor Thomas Nagel, who is perhaps most famous within the philosophical world for his classic paper What Is It Like To Be a Bat?.

An interesting quote:

Although I seem to be constitutionally incapable of religious belief, I find the contemptuous attitude toward it on the part of prominent secular defenders of evolutionary naturalism intellectually unreasonable. Unless one rules out the idea of divine intervention a priori (and setting aside the problem of evil), some version of the argument from design seems to me a perfectly respectable reason for taking that alternative seriously – no less so now that Darwinian theory has been elaborated through the great discoveries of molecular biology.

I believe there is something wrong with the way the dispute has been conducted, for example in recent arguments over the teaching of evolution in public schools. It is usually treated as if it were a dispute over whether the biological order proves the existence of a designer, and that is not the only way to see it. To be sure, the most famous use of the argument from design is as a proof of God’s existence, starting from nonreligious premises about the natural world. Seen in this way, the question posed by the defenders of intelligent design is whether an atheist is forced by the empirical facts of nature to acknowledge that the appearance and evolution of life cannot be explained except by the agency of a purposeful designer.

No doubt some defenders of intelligent design make that claim, but while this is a legitimate question, it doesn’t get at the main difference between the parties to this dispute, a difference that remains even if the atheist can rationally resist any nonmechanistic explanation. The real issue, I suggest, is not whether the biological facts do or do not rationally require belief in God, but rather how an antecedent belief or disbelief in the existence of God will reasonably affect one’s interpretation of the biological facts.

Most people are believers or nonbelievers in the existence of God not as a result of argument, but in a much more basic way. They either see or experience God’s presence in the world and in their lives or they don’t. If God exists, then the capacity to see God’s will expressed in the world is one of the forms of perception he has given us, the sensus divinitatis. If God does not exist, then it is a form of illusion. As Alvin Plantinga has argued –- persuasively, in my view -- the justification for such religious belief is inseparable from its truth, just as is the case with sensory perception. We can’t construct a justification by starting from purely subjective data and inferring that God provides the only possible explanation of those data, any more than we can prove the existence of the physical world that way. But that doesn’t show that either perceptual or religious beliefs are unwarranted. Whether they are depends on whether they are delivered by reliable human faculties.

If one believes in God already, that belief will naturally form a part of the way one understands other things one knows about the world. If on the other hand one doesn’t regard the existence of God as a serious possibility, it will not be included among the resources that could conceivably be used to make sense of anything else. To someone for whom the possibility of an interventionist god is simply ruled out in advance, any problems in working out a purely mechanistic account of the evolution of life are nothing but intellectual challenges to evolutionary theorists to develop the theory further. There is no available alternative to an explanation in terms of chemistry and physics. To a believing Christian, on the other hand, the question is naturally open. After all, if God is responsible for the character of the world, including our existence, this responsibility might have been exercised only by establishing the eternal laws of physics, or it might have been exercised more specifically, by ordaining further principles, processes, or events not determined by the laws of physics.

Both the Christian and the atheist can agree that the hypothesis of intervention in the physical order by a creator, perhaps through the creation of very special initial conditions, would render the observed biological facts at least as likely as the hypothesis of blind physical forces, working ultimately through the processes of mutation and natural selection. But to an atheist the former hypothesis has zero antecedent likelihood, so there is no contest. It can be safely ignored, like the hypothesis that an otherwise inexplicable misfortune that has happened to me can be explained by witchcraft. Most of us would dismiss that hypothesis even if the misfortune followed the sincere attempt by one of my enemies, fresh from an overdose of Harry Potter, to cast an evil spell on me.

To a Christian, the possibility of divine intervention in the natural order is not ruled out in advance. Therefore the fact that such intervention would render certain observed facts probable is evidence in its favor, and it becomes one of the possible explanations of facts that might also be explained naturalistically, but that are by no means rendered more probable by the assumption of pure mechanism than they would be by purposive intervention. Perhaps on Christian assumptions it is a question left open by the available evidence, but it will certainly not be reasonable to think, as atheists naturally do, that there must be a purely mechanistic explanation of the origin and development of life.

To claim that that is the only reasonable conclusion for anyone to draw from the empirical data, the defender of evolutionary theory would have to claim that the belief in a god who can intervene in the world, like the belief in witchcraft, is itself irrational, and that it has been refuted by science. I am sure there are atheists who believe this, even if many of them would be reluctant to say so –- for reasons of tact if not of political prudence. But I believe they are mistaken: Neither belief nor disbelief in God is irrational, and the consequence is that two diametrically opposed attitudes toward the natural order are both reasonable.