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This is the 49th post in my Theories of Knowledge and Reality series. The last post looked at one final argument for dualism from Gottfried Leibniz and led into an argument instead in favor of materialism based on materialism offering the simplest explanation. This post looks at one further argument against dualism.

Substance dualism takes there to be two fundamental sorts of thing in the universe - physical stuff and minds. (A substance for philosophers is not some icky, gooey stuff but a technical term for whatever counts as a real, genuine thing.) Materialists just accept the physical, so they have no problem of how the two interact. [Similarly, Berkeley's idealism has just the mental, so he has no such problem.] A dualist who believes minds are non-physical things will have to explain how (if at all) mental stuff and physical stuff interact causally. This kind of dualism is sometimes called interactionism.

Dualists often do not give a mechanism to explain this interaction. They usually just take it to happen, treating it as a mystery. There are mysteries in the universe, and our ignorance of the mechanism doesn't make it false that there is one. This isn't super-satisfactory, but the objection isn't devastating. After all, materialists don't have a similar, well-developed explanation about how physical matter leads to thinking. The real problem involves a principle of physics - the law of conservation of matter and energy. This law states that matter and energy can interact and be converted into each other, but the total of all of it doesn't change. If minds can cause things in the physical realm, and vice-versa, then the physical events leading up to a mental event somehow must get the mental event to happen. Does that expend energy? If so, then the energy is somehow transferred into the mental realm. Something similar would happen for the other way around. Doesn't that violate the law of conservation?

The dualist has a fairly easy reply, one overlooked in most of the literature. Not too long ago, there were two conservation laws. Physicists thought the realm of matter and the realm of energy were constant and separate. They believed in no interaction between the two, no conversion from one to the other. They were wrong. Perhaps the objector is making the same mistake. Perhaps we need to be willing to consider the possibility that the correct law of conservation includes mental stuff in it along with matter and energy. If so, then the objection isn't anywhere near as powerful, though materialists still might not be satisfied by this response. There is textual evidence that such a reply is very much in the spirit of Descartes.

The next post will look at a different kind of dualist view that responds to this criticism in a very different way.


I have a question. If materialism is true then how can the content of a belief or thought effect the thinking process? I would assume that we would not be reasoning in the classic sense, but we would simply believe or conclude what the underlying, non-rational physical process caused us to believe.

Is that correct?

Materialists generally say that there are two levels of description. On the level of reasons and intentions, our intentions cause what we do. On the level of description of brain processes, those cause what we do Materialists would then say that both levels describe the same reality. But these are actually different kinds of causes too, classically. Aristotle would call the higher-level causes final causes and the lower level ones efficient causes.

But I wonder from the last part if you're smuggling the issue of determinism in also, which I think is a completely separate issue. Leibniz was a deterministic dualist, as the next post will make clear, and Peter van Inwagen is a prominent materialist indeterminist.

Hi Jeremy,

I was wondering if you think the alleged interaction problem could also be raised against theism, as God is supposed to be a spiritual being who interacts with and upholds matter?

If you're thinking of miracles as God suspending the laws of physics, then you do get a worry like this. But it's not the same worry, because miracles, if exceptions to the laws, wouldn't have to follow conservation laws either. Presumably there are natural laws that govern how minds and bodies interact, if dualism is true. Even if those laws are broader than the laws of physics, do the laws of physics not apply to the physical matter that's involved in the interaction? With miracles (conceived of as violations of laws), you have it built in that the laws of physics aren't necessarily in play. With ordinary, everyday mental causation of physical events or vice versa, dualists don't typically want to say that.

Also, one model of divine interaction avoids the problem easily. If God interacts with the physical universe by setting it up according to laws that he then violates, you get this. But if the laws include everything that happens, and the conservation laws are just a rule that physical stuff normally follows when some higher law isn't in play, then there's no issue at all, and it doesn't deny law-governedness. I think there are a lot of assumptions in these discussions that you need to get out of the way at the beginning before you get the discussion going. Most discussions of miracles assume a controversial model of God's interaction with the universe and don't consider other models.

Interesting, although I wasn't thinking along the lines of miracles. Although God setting up physical laws that operate independently of him is one way to look at the picture, I think of his interaction with physical laws as much more intimate. That is, his existence sustains the laws, so that if he ceased to exist (per impossible), the laws would cease to operate.

So the question could be phrased, How can an entity such as God who is entirely non-material (as generally defined) possibly interact (/sustain, etc.) with an entirely different type of thing, viz. physical stuff?

If this question isn't fallacious in some sort of way, than all classical theists would have to deal with it, whether or not they are dualists with respect to *human* minds. What do you think?

I was wondering whether I should get into something like Aquinas' doctrine of continuous creation, but I thought that might complicate things. It's not exactly God's existence that sustains things, on his view, but God's will.

If you want to extend the question to how God sustains the universe, you might as well continue to extend it to how God created physical matter to begin with. I don't think any traditional theist is really going to spend a lot of time worrying about that problem. You might as well ask how an omnipotent being can do anything.

Granted, but if God didn't exist, his will wouldn't exist, which would end in the same result.

I'm not really concerned with asking how exactly God sustains the universe, but just pointing out that in sustaining it, his will is (in a way) interacting with matter. So the theist has to deal with the alleged interaction problem with respect to God and matter, even if he is not a dualist with respect to human minds. See what I mean?

I didn't mean to suggest that the difference between what you said and Aquinas' view will amount to anything on this issue. I just didn't want to give the impression that he holds the view you said, just one that's similar and with the same result.

What I said is that you can push one aspect of the same question there, but once you do you'll have to push it to a question that no theist will find remotely plausible as a critique of theism, which suggests that it's not really an appropriate question.

But that's only one aspect of the interaction problem. It's sometimes presented as a question of how this mysterious interaction takes place. I think that's a mistaken way to think of the problem, though. The problem most materialist philosophers present it is not wondering at how the mysterious influence takes place. It's much more seriously a worry about how conservation laws are consistent with interaction from outside the system. Depending on how you construe God's interaction with creation, it may not be interaction from outside the system at all, and thus you easily dodge the more serious worry that materialists have.

I remember having exactly that discussion with a hardcore atheist and anti-ID geology professor who thought intelligent design violated the laws of conservation. He had nothing to say in response when I explained how ID arguments can get off the ground just as easily if you assume an entirely deterministic framework where God just sets up the laws in advance with a certain goal in mind. He apparently hadn't ever thought about that possibility, but it's one of the major options in the history of philosophy for thinking about God's interaction with creation, endorsed by as important a figure as Leibniz, who also happened to think ID arguments are pretty good support for theism.

Thanks Jeremy, that answers my question. Paragraph 3 of your last response was particularly helpful.

Conservation of energy is a red herring. It only applies to a closed system. But even if we could test a person's mind in a completely closed system, there would still be no violation since all that would happen is that potential energy was converted into kinetic energy. When the potential energy runs out, so does the kinetic energy. In other words, people get tired and the body part of the mind-body duality fails.

WRT miracles, the laws of conservation of energy need not apply as you've stated, but they could just as easily be handled by the conversion of potential energy into kinetic or vice versa. God's interactions may even be simpler than that. He may just play with probabilities and make something highly improbable highly probable for a limited time.

By the laws of physics, it's possible for all the air to huddle in the corner and suffocate you. It's possible, but it would be extremely improbable. Similarly, it's possible for all the water under your feet to freeze so you can walk on water and unfreeze afterwards. It's possible, but it would be extremely improbable.

Mind-body duality may simply a limited version of this probability manipulation. Alternately, it may be the cause of potential energy being converted to kinetic.

There are many other models of mind-body duality, and I don't think it's wrong to make experimentally verifiable models to prove one's case. There are many things in the Bible, such as Pontius Pilate, which were thought to be mythical for centuries but were recently proven true. If the Bible is true, it corresponds to reality, which means that it should be verifiable, at least in the ordinary miracles such as life.

Conservation of matter and energy isn't a red herring. It does only apply in a closed system, but its confirmation in physics is usually taken as a sign that the physical universe is a closed system. That's not a red herring. It's a particularly strong argument that dualism has to deny something that has the status of a law in contemporary physics.

I don't understand your argument about potential and kinetic energy. The kinetic energy can't run out in a closed system. It has to be converted to matter or some other form of energy. According to the conservation laws, it can't just disappear and then some effect occurs in something non-physical. It's especially hard to see how a physical effect could occur with no physical cause if the universe is closed. It's perhaps uncertain that the universe is closed, but the strength of the argument is that we do assume this in science, and there's never been any reason to think otherwise. There's certainly no evidence of anything to the contrary.

I don't think you could describe playing with the probabilities the way you do as possible in a closed system. The probabilities are determined by a set of equations, and if those equations were to be changed it would mean something outside the closed system has interfered. It's still an interference.

I'm not sure if you're suggesting a reductionist account of mind-body duality in terms of potential/kinetic energy or in terms of probability manipulation. If so, those are physical processes, and it wouldn't be dualism. It would be a version of materialism. If that's not what you're suggesting, I'm afraid I don't understand what you're saying.

WRT conservation of energy, look at it this way. If you use the universe as being the closed system, you immediately run into one problem. How do you know you're actually violating it? Consider the case of a unidirectional worm-hole. Matter/energy would enter at one side and exit at the other. CoE isn't being violated, but if you were at the exit point, it would appear that it was. You would only know for sure if you knew about the entry point. But it's a big universe, so how would you know? Science is no-where near at the point where we could test this, so dismissing dualism based on a CoE is assuming that we know something that we don't.

From another angle, CoE isn't sacred. Some naturalistic explanations for the Big Bang violate CoE on a massive scale (e.g. the multiverse explanation or the defunct Steady State model) without raising an eyebrow. CoE is true to our experience, in much the same way that Newtonian mechanics are true to our experience, but if something more accurate comes along on the scale of Relativity for certain special cases, it wouldn't be that big an issue for science as long as our common experience wasn't violated. So, maybe CoE actually is being violated in the brain. Has anyone actually done a test to confirm that CoE is being violated in the brain? If not, then the skeptic is again assuming something that we don't know.

WRT probabilities, living systems aren't state machines, they involve a source of randomness (a.k.a. quantum phenomenon), so brains in the materialist's world are stochastic processes. Everything around is also also a combination of random and deterministic components, so they are also stochastic processes. Random processes, by definition depend on probabilities. A non-physical being (i.e. non-material being or material being outside our 3D material universe) could interact with our universe without violating CoE simply by adjusting the probabilities. That's one way thought could be possible and one way miracles could be possible without violating CoE. In a practical example. Imagine that you have deterministic machine that walks, but uses a dice to determine where it walks. If left alone, the robot would do a drunkards walk. Now if I hand you a loaded die, the robot would move in a specific direction without violating CoE. I could change the die, outside the universe, causing the robot to move in another direction, without violating CoE. The nice thing about this mechanism, is that because it involves probabilities, it is possible to do statistical tests to determine if the system really is random or if something non-physical is pulling the strings. Science isn't at the point where we can test this, but it is theoretically possible.

WRT kinetic/potential, imagine deterministic car that just moves forward. How could I cause the car to turn left without adding energy to it? Suppose non-physical being (i.e. non-material being or material being outside our 3D material universe) could cause any process to sponaneously convert energy from kinetic into potential or vice versa. This being could cause the rotational kinetic energy from the left wheels to be converted into tension potential energy (i.e. as in a spring). The left wheels could stop working while the right wheels keep working. This would cause the car to turn left. This externally manipulated process would not violate CoE and it might actually be a bit easier to measure than the probability manipulation if the excess potential energy of an action like 1000 left turns without a right turn is radiated off as heat.

In any case, the the grounds of science, we just don't know enough about the mind to draw any conclusions, so the only honest position is to remain agnostic, even if we choose to have faith in one world view or another. The same can be said about miracles.

I don't see how the first paragraph of the last comment helps. A wormhole connects two physical things. So not being able to show if conservation laws are violated in that case doesn't tell you anything about how dualism can handle this problem. That example only explains how physical-physical causation might occur without being able to show it occurs. This problem is about whether physical-nonphysical causation could occur. Maybe you're just pointing out how conservation laws aren't all that established, as you go on to say in the second paragraph, but I got the impression that this was a separate argument. I agree fully with your second paragraph, by the way.

My point about probabilities is that the laws of physics determine what the probabilities are, so changing the probabilities would require changing the way matter and energy are arranged so as to generate a different probability function. To cause energy to convert forms is to make a change, unless the laws of physics are violated. If a constant state suddenly does something that the laws of physics wouldn't have gotten it to do, you have to have violated some law, whether it's a closed system or not. Views that take miracles to be law-violations already accept that. Views that don't have to think of it as front-loaded in a deterministic (or deterministic enough) system.

I certainly disagree with you about agnosticism being the only position. I think there's a pretty good argument for dualism, but it's not going to show up immediately. We have to get through the personal identity topic first, since it depends on all the materialist views on that issue being so implausible as to be ridiculous.

I guess my argument may be summed up as follows:

(a) We do not know if conservation of energy is happening in the brain (no surprise since it's hard to measure), so we cannot assume it to be so in an argument against dualism.

(b) Conservation of energy isn't sacred for materialists since they are willing to throw it out to explain things such as the Big Bang, so even if dualism required violating CoE, the dualist can simply claim that CoE isn't sacred (at least until a resolution on (a) happens) on the same ground that materialists claim.

(c) But even if conservation of energy appears to hold in (a), dualism does not require CoE to be violated. There are mechanisms in our apparently stochastic world that allow for directed manipulation of matter (i.e. our brains) without violating CoE through probability manipulation (see the robot example). Yes, it takes energy to change dice, but the dualist assumes that the material 3D universe is not all there is so that the dice do not live in our material 3D universe. As a consequence, changing the dice outside or material 3D universe will require no energy change within our universe and the CoE will not be violated.

So CoE is a distraction. It neither helps nor harms the dualist's arguments.

That's the best I can explain. If you remain unconvinced, I apologize for my inability to communicate or inability to see where you see a problem.

Please continue the series. I'm eager to see your followup articles.

I agree with (a).

Materialists generally think the conservation laws apply once the laws are in effect but not beforehand, so the Big Bang might be a legitimate exception. I don't find (b) compelling. The laws are a contingent matter. It would be different to insist on denying the need for explanations at all when it comes to the universe but only for the universe, which a lot of atheists do to get around the cosmological argument. That seems to me to accept a principle that seems to be necessarily true, then allow one exception, for reasons that I can see only to be question-begging in terms of the cosmological argument. Here it's accepting an exception to a law that's only contingent and may not even have been true for the whole history of the universe but still insisting that the law remains true for all time once it's in effect given a stable universe. That doesn't seem anywhere near as problematic.

On (c), I'm not sure how having the dice outside the material universe makes a difference. The objective probabilities are determined by the arrangement of matter and energy in the physical universe and governed by equations that are purely a matter of physics. To change those, you'd need to change something about the arrangement of matter and energy. Even if the cause of changing them is outside the physical universe, it would be a change in the supposedly-closed system caused by nothing in the closed system. You'd have to have probabilities that aren't fully determined by anything in the closed system and therefore aren't determined by anything (since it's not a closed system if they're determined by something outside the system). That's metaphysical impossible, for one thing, because there wouldn't be any probabilities if there weren't anything determining what they are. But it's also no help in the question at hand, since we need mental stuff to determine the probabilities, not nothing determining them. Unless I'm misunderstanding your proposal, I'm not sure it retains the assumption of a closed universe while explaining how something outside the closed universe nevertheless causes things in the closed universe.

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