Having argued last week that prayer provides benefits for believers that are not available for atheists, I was interested to come across an academic paper by Tim Mawson that argued atheists have an obligation to pray to God that he stop them being atheists.

Mawson says his argument only works for atheists "who assign anything greater than a negligible probability to God's existence". In that respect, his is just the latest in a long line of arguments that use the mere possibility that God exists as a reason to be religious, or at least give it a go.

The most famous of these is Pascal's Wager, which, in a nutshell, says that you have more to lose by not believing and being wrong than you do by believing and being wrong, and more to gain by believing and being right than not believing and being right. Critics protest that this is only true if all outcomes were equally likely, but if there is only a minuscule chance that God exists, the odds aren't worth taking. To which the reply is: the stakes here are so high, even an incredibly long shot is worth a go.

I think there is a fairly decisive response to this, which also takes care of Mawson. But it also has a more interesting positive corollary: it shows why belief in God doesn't matter. Even if we think it is more likely God exists than not, we should not bother to believe in him. (Apologies for the masculine pronoun, but I defer to the conventions of those who believe.) I won't call it Baggini's Wager, in part because I'm sure I'm not the first to think of it. So let's call it Homer's Wager, for reasons that will soon become clear.

Here's how it works. Let's start with the very generous assumption that we think it more likely than not that God exists. To put a number on such things is ridiculous of course, but for the sake of argument, we'll use the figure of 67% which was the one a risk assessor came up with a few years ago. You might think that, if this is true, you should believe in God. But here's the problem: does it matter which God you believe in?

Maybe it doesn't matter, but it does matter if it matters. If it doesn't matter which God you believe in, it's because there are no important rewards or penalties for believing in the right or wrong God. But if that's the case, then it would not seem to matter if you didn't believe at all. A God who didn't care if you got belief right would hardly come down hard on those who didn't believe at all. I think we can safely conclude that the probability of a liberal God fascist – one who doesn't mind which version of him you believe in, but if you don't believe in him at all, he'll let you rot in hell – is negligible. As Homer Simpson put it when arguing that he shouldn't go to church: "Don't you think the almighty has better things to worry about than where one little guy spends one measly hour of his week?"

So if it doesn't matter whether you believe in such a vague God or not, you have no compelling reason to bother. The atheist bus slogan could just as easily be "There's probably a God. Now stop worrying and enjoy your life".

If, on the other hand, it matters which God you believe in, it's because there are certain important rewards of belief that you will not receive if you don't believe in the right one, or punishments for failing to believe correctly. But even Homer Simpson can see the problem with this: "What if we've picked the wrong religion? Every week we're just making God madder and madder?" Choosing the wrong God might be worse than believing in none at all.

So to continue with the mad maths, even if you think it more than 50% likely that a God exists who will treat you differently – not just over the next few short years of your life but for all eternity – whether you believe in him or not, you still have no reason to believe in such a God, because you simply can't know which one to go for and life is too short to try them all out. In case you think that's overstating it, you only need to go into one church to find that there are almost as many Gods worshipped there as there are worshippers.

Mawson can see there is a problem about which God you should pray to and tries to get around this by saying the prayer should be a very open one, like "Is there anyone there?" or "God, if you're there, please speak to me". This is fine, but it makes his argument's conclusion much weaker than it appears in headline form.

From time to time, I'm happy to make such a request. There – I've just done it. No reply. Again. Let's move on. After all, millions of people have done this millions of times and the number who have felt their prayer was answered in the affirmative is no more than you'd expect by chance, which is bound to occasionally throw together the utterance of a prayer and the occurrence of something that looks like its answer.

Mawson also accepts that his argument, like other probabilistic ones, only works for atheists "who think that the issue of God's existence or non-existence is an important one". What Homer's Wager makes clear is that, in fact, it isn't and it's pretty hard to see why it should be. It's only important if you think that a God would seriously reward true believers and/or severely punish infidels, and I think the probability of such a petty, spiteful God existing is negligible. Even if it isn't, you can only do something about it if you think you have a good chance of discovering what this God really wants.

Homer's Wager therefore concludes that you have no good reason to believe in God, even if it is more likely than not that he exists, let alone if you are among those of us who think the probability is closer to 6.7% than 67%. And what this shows is that the issue of God's existence or non-existence is not an important one after all.

Why then do people like myself take such an interest in religion? Because religion is an important issue, not the existence of God. If that's right, it might help explain why the endless arguments about God's existence don't lead us anywhere. It looks like the central question of religion, but it isn't.

That last suggestion needs much more unpacking and defending. Give me a week or so to think about it…

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