William Lane Craig proposed the following argument for God's existence:
For those who are unfamiliar with the argument for God from the applicability of mathematics to the physical world, here is a simple formulation I have used:
- If God does not exist, the applicability of mathematics to the physical world is just a happy coincidence.
- The applicability of mathematics to the physical world is not just a happy coincidence.
- Therefore, God exists.
I agree with you that this is an extremely persuasive theistic argument. Just look how Alex Rosenberg stumbles around it when I proposed it in my debate with him! [1]
Source: #608 God and the Unreasonable Effectiveness of Mathematics | Reasonable Faith
Subsequently, this argument became the topic of a debate between Willian Lane Craig and Graham Oppy: Does Math Point to God? William Lane Craig + Graham Oppy.
Among the many things Oppy said, one of his main rebuttals focused on asserting that, even if it's in fact the case that mathematics can be applied effectively to the physical world, this applicability can be postulated as a necessary brute fact, thus not requiring further explanations (as necessary things explain themselves). On the contrary, Craig kept on insisting that the surprising applicability of mathematics to the physical world cries out for an explanation, meaning that such an explanation is God, who must have been the responsible for intelligently designing the universe using mathematics.
Is it okay to postulate that the applicability of mathematics to the universe is a brute fact? Or is this something that, as Craig asserts, cries out for an explanation?
A relevant related discussion: Was mathematics invented or discovered?
Appendix
The transcript of part of the exchange between William Lane Craig and Graham Oppy (from t=55:05).
Bertuzzi: Graham, it sounds like if we could split the argument in two stages, stage 1 being about whether or not math does apply or does have this sort of uncanny applicability to the universe, if we labeled that stage 1 and then stage 2 is how do we explain this, is it evidence for theism, it sounds like you're wanting to go back to stage 1 and say "well I don't really know if mathematics does have this uncanny applicability".
Oppy: Right, so that's all I've argued about so far. But let me say something about the argument, right, because I think that it's not true that naturalists have no resources here. So suppose it's true that there's this fit between mathematics and physical structure, right, of the kind that we're imagining. There are versions of naturalism that can explain this in a very straightforward way. And so one of the versions of naturalism can do this is one that I've been playing around with for about a decade now. And so let me give you the kind of tenants of the theory that you need in order to explain the effectiveness. When I get to the end of it you may think it's, I don't know, disappointing that it turns out that this is the way the explanation goes but it's definitely an explanation. So, start with this. A theory of modality. So, every possible world shares some initial history with the actual world, diverges from it only because chances play out differently. So that's all the possibilities there are. The only possibilities that you need really of a chance. Only talking metaphysics here, we're not talking doxastic possibilities or epistemic possibilities, we're talking metaphysical possibilities. So that's all the possibilities that there are. The laws are necessary, the boundary conditions are necessary. This is true and it doesn't matter whether we're thinking about one universe or many universe model. So we're supposing that where contingency comes in is in the outplaying of chances, that's the only place that contingency comes in. We suppose also--and this is the only kind of new assumption that we're going to make to go along with the kind of metaphysical picture that we've already outlined which is going to be a naturalistic picture--that the laws and the boundary conditions are amenable to mathematical formulations. On that assumption and given the other assumptions it just turns out that it's necessary that that's the case. It couldn't possibly have failed not to be so. Now adding a couple of other things that I don't really need just but that are also part of this picture that I developed when I was thinking about the origins of the universe (it had nothing to do with the applicability of mathematics), there's no explaining why something's necessary. Once you get to the postulation of necessities you've reached the end of the explaining that you can do. And last of all, if you've got a non-modal claim P net and you believe it, you accept that necessarily P, then it's being necessary that P explains why P. Okay, so now, given that, we have an explanation for the effectiveness of mathematics, which is that it had to be. Because it had to be so. And it just falls out of the picture. Now that's a naturalistic story that has an explanation. You might not like the explanation but at least for me it comes for free, from things that I've said elsewhere.
Craig. Well, I hope that our listeners have understood your alternative because, honestly Graham, I think it takes you more faith to believe that than it does to believe in God! The claim for example that the mathematical formulation of the physical world is necessarily true, that just doesn't seem to be correct at all. There might have been no physical universe whatsoever, in which case mathematics would not be applicable, because there would be no physical universe. Or there might have been a sort of chaos. Albert Einstein wrote to Maurice Sullivan in 1952:
"One should expect a chaotic world which cannot be grasped by the mind in any way. One could, yes, one should expect the world to be subjected to law only to the extent that we order it through our intelligence. By contrast, the order created by Newton's theory of gravitation, for instance, is wholly different. Even if the axioms of the theory are proposed by man, the success of such a project presupposes a high degree of ordering of the objective world and thus could not be expected a priori. That is the miracle which is being constantly reinforced as our knowledge expands."
So even so great a mathematical physicist as Einstein thought that it was a contingent matter that the world should exhibit this sort of mathematical order. That we should have expected, on the contrary, a chaotic world.
Bertuzzi: Well, let's get a response from dr. Oppy and then we'll move to some Q&A. So unfortunately we do have to move on.
Oppy: So when you talk about expectation, you may be talking about something epistemic or doxastic. I was talking about metaphysics. I was doing metaphysics and and my claim is that this is the best metaphysical theory. I'm not saying that it's true a priori. I'm saying that it's the best metaphysical theory when you take everything into account.
Craig: Can you specify, Graham, for us in a sentence or two why is it the best metaphysical theory in your view?
Oppy: Because if you think about the goal of theorizing, what you're trying to do is strike the best balance between minimizing all of your theoretical commitments and maximizing the explanation that you can do. And I think that this theory strikes that sweet spot. That's the reason. But there's a lot of data and there are hundreds of data points that you have to think about if we're going to compare this theory say with a theistic theory so I've written elsewhere at considerable length about why I think that you should prefer the naturalistic story to the theistic story. It just turns out that the naturalistic story, so, because this is the point, when you are formulating your theory, you said naturalist just have no explanation. That's not true, here is a naturalistic theory that does have an explanation. And what needs to be argued is about which one is the better theory, and that's not something that's settled by these considerations. It's settled by general considerations.
Craig: Okay, it didn't sound very explanatory to me. But we'll leave it at.
Oppy: Well, do you think that you can't explain why something's the case by pointing out that it's necessary? Because that's all that's going on here.
Craig: Yeah, I mean, it's really a way of avoiding explanation by just begging the question and assuming that it's necessarily the case. And that is implausible and certainly not incumbent or there's nothing that would lead us to think that that's true.
Oppy: So that's not right though. We've got two theories and we're comparing their virtues. The theories are what they are, they say what they say. It turns out that on this naturalistic theory there is an explanation and the explanation is that this stuff is necessary.