The Stone is a forum for contemporary philosophers and other thinkers on issues both timely and timeless.

This is the first in a series of interviews about religion that I will conduct for The Stone. The interviewee for this installment is Alvin Plantinga, an emeritus professor of philosophy at the University of Notre Dame, a former president of both the Society of Christian Philosophers and the American Philosophical Association, and the author, most recently, of “Where the Conflict Really Lies: Science, Religion, and Naturalism.”

Gary Gutting: A recent survey by PhilPapers, the online philosophy index, says that 62 percent of philosophers are atheists (with another 11 percent “inclined” to the view). Do you think the philosophical literature provides critiques of theism strong enough to warrant their views? Or do you think philosophers’ atheism is due to factors other than rational analysis?

Alvin Plantinga: If 62 percent of philosophers are atheists, then the proportion of atheists among philosophers is much greater than (indeed, is nearly twice as great as) the proportion of atheists among academics generally. (I take atheism to be the belief that there is no such person as the God of the theistic religions.) Do philosophers know something here that these other academics don’t know? What could it be? Philosophers, as opposed to other academics, are often professionally concerned with the theistic arguments — arguments for the existence of God. My guess is that a considerable majority of philosophers, both believers and unbelievers, reject these arguments as unsound.

Still, that’s not nearly sufficient for atheism. In the British newspaper The Independent, the scientist Richard Dawkins was recently asked the following question: “If you died and arrived at the gates of heaven, what would you say to God to justify your lifelong atheism?” His response: “I’d quote Bertrand Russell: ‘Not enough evidence, God! Not enough evidence!’” But lack of evidence, if indeed evidence is lacking, is no grounds for atheism. No one thinks there is good evidence for the proposition that there are an even number of stars; but also, no one thinks the right conclusion to draw is that there are an uneven number of stars. The right conclusion would instead be agnosticism.

In the same way, the failure of the theistic arguments, if indeed they do fail, might conceivably be good grounds for agnosticism, but not for atheism. Atheism, like even-star-ism, would presumably be the sort of belief you can hold rationally only if you have strong arguments or evidence.

The failure of arguments for God would be good grounds for agnosticism, but not for atheism.

G.G.: You say atheism requires evidence to support it. Many atheists deny this, saying that all they need to do is point out the lack of any good evidence for theism. You compare atheism to the denial that there are an even number of stars, which obviously would need evidence. But atheists say (using an example from Bertrand Russell) that you should rather compare atheism to the denial that there’s a teapot in orbit around the sun. Why prefer your comparison to Russell’s?

A.P.: Russell’s idea, I take it, is we don’t really have any evidence against teapotism, but we don’t need any; the absence of evidence is evidence of absence, and is enough to support a-teapotism. We don’t need any positive evidence against it to be justified in a-teapotism; and perhaps the same is true of theism.

I disagree: Clearly we have a great deal of evidence against teapotism. For example, as far as we know, the only way a teapot could have gotten into orbit around the sun would be if some country with sufficiently developed space-shot capabilities had shot this pot into orbit. No country with such capabilities is sufficiently frivolous to waste its resources by trying to send a teapot into orbit. Furthermore, if some country had done so, it would have been all over the news; we would certainly have heard about it. But we haven’t. And so on. There is plenty of evidence against teapotism. So if, à la Russell, theism is like teapotism, the atheist, to be justified, would (like the a-teapotist) have to have powerful evidence against theism.

G.G.: But isn’t there also plenty of evidence against theism — above all, the amount of evil in a world allegedly made by an all-good, all-powerful God?

A.P.: The so-called “problem of evil” would presumably be the strongest (and maybe the only) evidence against theism. It does indeed have some strength; it makes sense to think that the probability of theism, given the existence of all the suffering and evil our world contains, is fairly low. But of course there are also arguments for theism. Indeed, there are at least a couple of dozen good theistic arguments. So the atheist would have to try to synthesize and balance the probabilities. This isn’t at all easy to do, but it’s pretty obvious that the result wouldn’t anywhere nearly support straight-out atheism as opposed to agnosticism.

G.G.: But when you say “good theistic arguments,” you don’t mean arguments that are decisive — for example, good enough to convince any rational person who understands them.

A.P.: I should make clear first that I don’t think arguments are needed for rational belief in God. In this regard belief in God is like belief in other minds, or belief in the past. Belief in God is grounded in experience, or in the sensus divinitatis, John Calvin’s term for an inborn inclination to form beliefs about God in a wide variety of circumstances.

Nevertheless, I think there are a large number — maybe a couple of dozen — of pretty good theistic arguments. None is conclusive, but each, or at any rate the whole bunch taken together, is about as strong as philosophical arguments ordinarily get.

G.G.: Could you give an example of such an argument?

You don’t even need arguments to have a rational belief in God. Belief in God is grounded in experience.

AP: One presently rather popular argument: fine-tuning. Scientists tell us that there are many properties our universe displays such that if they were even slightly different from what they are in fact, life, or at least our kind of life, would not be possible. The universe seems to be fine-tuned for life. For example, if the force of the Big Bang had been different by one part in 10 to the 60th, life of our sort would not have been possible. The same goes for the ratio of the gravitational force to the force driving the expansion of the universe: If it had been even slightly different, our kind of life would not have been possible. In fact the universe seems to be fine-tuned, not just for life, but for intelligent life. This fine-tuning is vastly more likely given theism than given atheism.

G.G.: But even if this fine-tuning argument (or some similar argument) convinces someone that God exists, doesn’t it fall far short of what at least Christian theism asserts, namely the existence of an all-perfect God? Since the world isn’t perfect, why would we need a perfect being to explain the world or any feature of it?

A.P.: I suppose your thinking is that it is suffering and sin that make this world less than perfect. But then your question makes sense only if the best possible worlds contain no sin or suffering. And is that true? Maybe the best worlds contain free creatures some of whom sometimes do what is wrong. Indeed, maybe the best worlds contain a scenario very like the Christian story.

Think about it: The first being of the universe, perfect in goodness, power and knowledge, creates free creatures. These free creatures turn their backs on him, rebel against him and get involved in sin and evil. Rather than treat them as some ancient potentate might — e.g., having them boiled in oil — God responds by sending his son into the world to suffer and die so that human beings might once more be in a right relationship to God. God himself undergoes the enormous suffering involved in seeing his son mocked, ridiculed, beaten and crucified. And all this for the sake of these sinful creatures.

I’d say a world in which this story is true would be a truly magnificent possible world. It would be so good that no world could be appreciably better. But then the best worlds contain sin and suffering.

G.G.: O.K., but in any case, isn’t the theist on thin ice in suggesting the need for God as an explanation of the universe? There’s always the possibility that we’ll find a scientific account that explains what we claimed only God could explain. After all, that’s what happened when Darwin developed his theory of evolution. In fact, isn’t a major support for atheism the very fact that we no longer need God to explain the world?

A.P.: Some atheists seem to think that a sufficient reason for atheism is the fact (as they say) that we no longer need God to explain natural phenomena — lightning and thunder for example. We now have science.

As a justification of atheism, this is pretty lame. We no longer need the moon to explain or account for lunacy; it hardly follows that belief in the nonexistence of the moon (a-moonism?) is justified. A-moonism on this ground would be sensible only if the sole ground for belief in the existence of the moon was its explanatory power with respect to lunacy. (And even so, the justified attitude would be agnosticism with respect to the moon, not a-moonism.) The same thing goes with belief in God: Atheism on this sort of basis would be justified only if the explanatory power of theism were the only reason for belief in God. And even then, agnosticism would be the justified attitude, not atheism.

G.G.: So, what are the further grounds for believing in God, the reasons that make atheism unjustified?

A.P.: The most important ground of belief is probably not philosophical argument but religious experience. Many people of very many different cultures have thought themselves in experiential touch with a being worthy of worship. They believe that there is such a person, but not because of the explanatory prowess of such belief. Or maybe there is something like Calvin’s sensus divinitatis. Indeed, if theism is true, then very likely there is something like the sensus divinitatis. So claiming that the only sensible ground for belief in God is the explanatory quality of such belief is substantially equivalent to assuming atheism.

G.G.: If, then, there isn’t evidence to support atheism, why do you think so many philosophers — presumably highly rational people — are atheists?

Some people simply don’t want there to be a God. It would pose a serious limitation for human autonomy.

AP: I’m not a psychologist, so I don’t have any special knowledge here. Still, there are some possible explanations. Thomas Nagel, a terrific philosopher and an unusually perceptive atheist, says he simply doesn’t want there to be any such person as God. And it isn’t hard to see why. For one thing, there would be what some would think was an intolerable invasion of privacy: God would know my every thought long before I thought it. For another, my actions and even my thoughts would be a constant subject of judgment and evaluation.

Basically, these come down to the serious limitation of human autonomy posed by theism. This desire for autonomy can reach very substantial proportions, as with the German philosopher Heidegger, who, according to Richard Rorty, felt guilty for living in a universe he had not himself created. Now there’s a tender conscience! But even a less monumental desire for autonomy can perhaps also motivate atheism.

GG: Especially among today’s atheists, materialism seems to be a primary motive. They think there’s nothing beyond the material entities open to scientific inquiry, so there there’s no place for immaterial beings such as God.

AP: Well, if there are only material entities, then atheism certainly follows. But there is a really serious problem for materialism: It can’t be sensibly believed, at least if, like most materialists, you also believe that humans are the product of evolution.

GG: Why is that?

AP: I can’t give a complete statement of the argument here — for that see Chapter 10 of “Where the Conflict Really Lies.” But, roughly, here’s why. First, if materialism is true, human beings, naturally enough, are material objects. Now what, from this point of view, would a belief be? My belief that Marcel Proust is more subtle that Louis L’Amour, for example? Presumably this belief would have to be a material structure in my brain, say a collection of neurons that sends electrical impulses to other such structures as well as to nerves and muscles, and receives electrical impulses from other structures.

But in addition to such neurophysiological properties, this structure, if it is a belief, would also have to have a content: It would have, say, to be the belief that Proust is more subtle than L’Amour.

Related More From The Stone Read previous contributions to this series.

GG: So is your suggestion that a neurophysiological structure can’t be a belief? That a belief has to be somehow immaterial?

AP: That may be, but it’s not my point here. I’m interested in the fact that beliefs cause (or at least partly cause) actions. For example, my belief that there is a beer in the fridge (together with my desire to have a beer) can cause me to heave myself out of my comfortable armchair and lumber over to the fridge.

But here’s the important point: It’s by virtue of its material, neurophysiological properties that a belief causes the action. It’s in virtue of those electrical signals sent via efferent nerves to the relevant muscles, that the belief about the beer in the fridge causes me to go to the fridge. It is not by virtue of the content (there is a beer in the fridge) the belief has.

GG: Why do you say that?

AP: Because if this belief — this structure — had a totally different content (even, say, if it was a belief that there is no beer in the fridge) but had the same neurophysiological properties, it would still have caused that same action of going to the fridge. This means that the content of the belief isn’t a cause of the behavior. As far as causing the behavior goes, the content of the belief doesn’t matter.

GG: That does seem to be a hard conclusion to accept. But won’t evolution get the materialist out of this difficulty? For our species to have survived, presumably many, if not most, of our beliefs must be true — otherwise, we wouldn’t be functional in a dangerous world.

Materialism can’t be sensibly believed, at least if, like most materialists, you also believe in evolution.

AP: Evolution will have resulted in our having beliefs that are adaptive; that is, beliefs that cause adaptive actions. But as we’ve seen, if materialism is true, the belief does not cause the adaptive action by way of its content: It causes that action by way of its neurophysiological properties. Hence it doesn’t matter what the content of the belief is, and it doesn’t matter whether that content is true or false. All that’s required is that the belief have the right neurophysiological properties. If it’s also true, that’s fine; but if false, that’s equally fine.

Evolution will select for belief-producing processes that produce beliefs with adaptive neurophysiological properties, but not for belief-producing processes that produce true beliefs. Given materialism and evolution, any particular belief is as likely to be false as true.

GG: So your claim is that if materialism is true, evolution doesn’t lead to most of our beliefs being true.

AP: Right. In fact, given materialism and evolution, it follows that our belief-producing faculties are not reliable.

Here’s why. If a belief is as likely to be false as to be true, we’d have to say the probability that any particular belief is true is about 50 percent. Now suppose we had a total of 100 independent beliefs (of course, we have many more). Remember that the probability that all of a group of beliefs are true is the multiplication of all their individual probabilities. Even if we set a fairly low bar for reliability — say, that at least two-thirds (67 percent) of our beliefs are true — our overall reliability, given materialism and evolution, is exceedingly low: something like .0004. So if you accept both materialism and evolution, you have good reason to believe that your belief-producing faculties are not reliable.

But to believe that is to fall into a total skepticism, which leaves you with no reason to accept any of your beliefs (including your beliefs in materialism and evolution!). The only sensible course is to give up the claim leading to this conclusion: that both materialism and evolution are true. Maybe you can hold one or the other, but not both.

So if you’re an atheist simply because you accept materialism, maintaining your atheism means you have to give up your belief that evolution is true. Another way to put it: The belief that both materialism and evolution are true is self-refuting. It shoots itself in the foot. Therefore it can’t rationally be held.

This interview was conducted by email and edited.

Gary Gutting is a professor of philosophy at the University of Notre Dame, and an editor of Notre Dame Philosophical Reviews. He is the author of, most recently, “Thinking the Impossible: French Philosophy Since 1960″ and writes regularly for The Stone.