I found this post on the Biola University Christian Thought blog. It’s by famous philosopher Alexander Pruss. In it, he considers 3 arguments against non-physical souls.

Here is the third objection:

The third objection is based on the Closure Principle: The physical world is explanatorily closed—the explanations of physical states of affairs are always physical in nature. The closure principle would let one be confident that scientists don’t need to look for miracles—that explanations of physical events will never go beyond science. If the Closure Principle is true, then no physical event in the brain has an explanation by means of a soul.

And here is his reponse:

I’m going to argue that the Closure Principle is more likely to be false than true.

My argument has two parts. The first part will be to establish the No Physical Explanation Thesis:

No Physical Explanation Thesis: Whether or not the Closure Principle is true, some physical states of affairs have no physical explanations.

The second part will argue that if the above thesis is true, then the Closure Principle is more likely to be false than true.

Sounds to me like he is just talking about the assumption of metaphysical naturalism, which some people accept because of the success of explaining nature using natural explanations. But can you really explain everything with only natural explanations?

Let’s see:

So, first, I need to argue that some physical states of affairs have no physical explanations. A quick argument for this thesis is to consider all of physical reality as a whole. This constitutes a gigantic physical state of affairs. This gigantic physical state of affairs cannot have a physical explanation. For if it had a physical explanation, that physical explanation would be a part of the gigantic physical state of affairs, since that gigantic state contained all of physical reality. But then the explanation, in explaining that gigantic state, would also explain itself, since it itself is a part of the gigantic state. But no physical state of affairs can explain itself—that would be like the absurdity of being one’s own parent.

A second (related) argument is that if every physical state of affairs has a physical explanation, we end up with a vicious infinite regress of physical states of affairs. Physical state #1 is explained by physical state #2 (maybe, my existence is explained by my parents’ existence), which then must be explained by physical state #3, and so on. So we have an infinite regress of physical states of affairs. But the regress does not stop there. For the whole infinite regress will be a physical state of affairs, and hence will need an explanation. So we will have another regress, and another, and so on. This is really absurd.

A third argument is that current science gives us good reason to think that physical reality is not infinitely old, that it came into existence some finite amount of time ago, maybe in a Big Bang. If so, then the state of affairs of physical reality coming into existence won’t have a physical explanation.

These three arguments for the No Physical Explanation Thesis are basically adaptations of the Cosmological Argument for the existence of God, but I am not concluding from them that there is a God—just that something physical has no physical explanation.

So now we’ve learned that some physical state of affairs has no physical explanation.

Let’s give a name to some such physical state of affairs—call it “Blob.” Blob, then, has no physical explanation. There are now two possibilities. Either (1) Blob has no explanation at all, or (2) Blob has a non-physical explanation.

If Blob has a non-physical explanation, then the Closure Principle is false, since the Closure Principle said that no physical state of affairs has a non-physical explanation, and here is Blob—a physical state of affairs with a non-physical explanation.

Of the two options, which is more likely? Blob having no explanation at all? Or Blob having a non-physical explanation? I will argue that think the likelier option is the latter—that Blob has a non-physical explanation.

For physical states of affairs are contingent—they don’t have to be there. Blob, thus, doesn’t have to be there. The idea of something contingent having no explanation is like the idea of something coming into existence out of nothing. It is intuitively absurd. Much more absurd than the alternative, namely that it has a non-physical explanation. Maybe it’s hard for something physical to happen because of a non-physical cause—but it should be far harder for something physical to happen for no cause at all. If we think that that something contingent could happen for no cause at all, it should be even easier for it to happen due to a non-physical cause. So it is more likely that Blob has a non-physical explanation than that it has no explanation at all. But if it has a non-physical explanation, then the Closure Principle is false. So, most likely, the Closure Principle is false.

Moreover, if we admitted that a physical state of affairs, namely Blob, could take place for no reason at all, with no explanation, then it would be a wonder why all sorts of other physical things don’t happen for no reason at all. Why doesn’t a dog-headed person suddenly pop into existence for no cause at all in front of me? Why doesn’t a golden mountain materialize in the middle of the Pacific Ocean out of nowhere? I can give a very simple explanation of why all these infinitely many strange things don’t happen: all physical states of affairs have to have explanations. But this explanation also implies that the Closure Principle is false. For we know that Blob has no physical explanation, and so Blob’s explanation must be non-physical.

The Closure Principle was introduced in large part to save science from giving up on physical explanations and looking for supernatural ones. But if we accept the Closure Principle, then we have to say that some physical states of affairs have no explanation at all. And it is much worse to be willing to give up completelyon a search for explanation than to be willing to give up on a search for physical explanation.

We should thus think that most likely the Closure Principle is false, and hence this argument against interaction between the soul and the body fails as much as the previous ones did.

This sounds a lot like William Lane Craig’s contingency argument, and I think that it is particularly mean (to the naturalists) to invoke science to smash their naturalism. I certainly accept non-physical causation when it comes to the origin of the universe – nothing too mysterious about that. And I think he’s right to say that this shows that it’s at least possible, then, that a non-physical entity could effect material things like our bodies. In fact, I’ve heard J.P. Moreland argue that this is what God actually is – a non-physical mind.