We have systematic overdetermination in our movements

The causal exclusion argument requires us to deny that there is systematic overdetermination between mental and physical causes.

But it is interesting to note that in the real world there is systematic overdetermination of physical movements. Suppose I raise my arm. My muscle contraction is caused by a bunch of electrons moving in the nerves between the brain and the muscle. Suppose there are N electrons involved in the electrical flow, for some large number N. But now note that except in extremely rare marginal cases, any N − 1 of the electrons are sufficient to produce the same muscle contraction. Thus, my muscle contraction is overdetermined by at least N groups of electrons. Each of these groups differs from the original N electron group by omitting one of the electrons. And each group is sufficient to produce the effect.

One might try to defend the no-systematic-overdetermination view by saying that what doesn’t happen is systematic overdetermination by non-overlapping causes. There are two problems with this approach. First, it is not empirically clear that there isn’t systematic overdetermination by non-overlapping causes. It could turn out that typically twice as many electrons are involved in nerve impulses as are needed, in which case there are two non-overlapping groups each of which is sufficient. Second, the anti-physicalist can just say that there is overlap between the mental cause and the physical cause—the mental cause is not entirely physical, but is partially so.

Alternately, one might say that there may be systematic overdetermination of physical events by physical events, but not of physical events by physical and mental events. This would need an argument.

The epistemic gap and causal closure

In the philosophical literature, the main objection to physicalism about consciousness is the epistemic gap: the alleged fact that full knowledge of the physical does not yield full knowledge of the mental. And one of the main objections to nonphysicalism about consciousness is causal closure: the alleged fact that physical events, like our actions, have causes that are entirely physical.

There is a simple way to craft a theory that avoids both objections. Simply suppose that mental states have two parts: a physical and a non-physical part. The physical part of the mental state is responsible for the mental state’s causal influence on physical reality. The non-physical part explains the epistemic gap: full knowledge of the physical world yields full knowledge of the physical part of the mental state, but not full knowledge of the mental state.

Having multiple sufficient causes

It would be useful for discussions of causal exclusion arguments for physicalism to have a full taxonomy of the kinds of cases in which one effect E can have two sufficient causes C₁ and C₂.

Here is my tentative list of the cases:

1. Overdetermination: C₁ and C₂ overdetermine E

2. Chaining: C_i sufficiently causes C_j which sufficiently causes E (where i = 1 and j = 2 or i = 2 and j = 1)

3. Constitution: C_i sufficiently causes E by being partly constituted by C_j which sufficiently causes E (where i = 1 and j = 2 or i = 2 and j = 1)

4. Parthood: C_i sufficiently causes E by having the part C_j which sufficiently causes E (where i = 1 and j = 2 or i = 2 and j = 1).

If parthood is a special case of constitution, then (4) is a special case of (3). Moreover (2)–(4) are all species cases of:

5. Instrumentality: C_i sufficiently causes E by means of C_j sufficiently causing E (where i = 1 and j = 2 or i = 2 and j = 1).

Note that the above cases are not mutually exclusive. We can, for instance, imagine a case where we have both chaining and overdetermination. Let’s say I aim a powerful heat gun at a snowball. Just in front of the snowball is a stick of dynamite. The heat melts the snowball. But it also triggers an explosion which blows the snowball apart. Thus, we have overdetermination of the destruction of the snowball by two causes: heat and explosion. However, we also have chaining because the heat causes the explosion.

I wonder if we can come up with an argument that (1)–(4), or maybe (1) and (5), are the only options. That seems right to me.

Causing via a part

Assume this plausible principle:

1. If a part x of z causes w, then z causes w.

Add this controversial thesis:

2. For any x and y, there is a z that x and y are parts of.

Thesis (2) is a consequence of mereological universalism, for instance.

Finally, add this pretty plausible principle:

3. All the parts of a physical entity are physical.

Here is an interesting consequence of (1)–(3):

4. If there is any non-physical entity, any entity that has a cause has a cause that is not a physical entity.

For if w is an entity that has a cause x, and y is any non-physical entity, by (2) there is a z that x and y are both parts of. By (3), z is not physical. And by (1), z causes w.

In particular, given (1)–(3) and the obvious fact that some physical thing has a cause, we have an argument from causal closure (the thesis that no physical entity has a non-physical cause) to full-strength physicalism (the thesis that all entities are physical). Whatever we think of causal closure and physicalism, however, it does not seem that causal closure should entail full-strength physicalism.

Here is another curious line of thought. Strengthen (2) to another consequence of mereological universalism:

5. The cosmos exists, i.e., there is an entity c such that every entity is a part of c.

Then (1) and (5) yield the following holistic thesis:

6. Every item that has a cause is caused by the cosmos.

That sounds quite implausible.

We could take the above lines of thought to refute (1). But (1) sounds pretty plausible. A different move is to take the above lines of thought to refute (2) and (5), and thereby mereological universalism.

All in all, I suspect that (1) fits best with a view on which composition is quite limited.

Ways out of the closure argument for physicalism

One of the main arguments for physicalism is based on the closure principle:

1. Any physical event that has a cause has a physical cause.

It is widely thought that it follows from (1) that:

2. If a physical event has a nonphysical cause, the event is overdetermined.

And hence in the absence of systematic overdetermination, mental causes must be physical.

But (2) doesn’t follow from (1). There are at least three ways for an event E to have two sufficient causes A and B:

• overdetermination

• chaining: A causes B which causes E or B causes A which causes E

• parthood: A causes E by having B as a part which causes E, or B causes E by having a part A which causes E.

Let’s think a bit about how the chaining and parthood options might avoid physicalism in the case of mental causation and yet allow for closure.

Option I: Nonphysical-physical-physical chaining: A nonphysical event M causes a physical event P which causes a physical event E. This can’t be the whole story for how we respect closure. For by closure, P will need a physical cause P₂, and so it is looking like P is going to be overdetermined, by M and P₂. But that does not follow without further assumptions. For we could have the following scenario:

• E is caused by an infinite chain of physical causes which chain is causally preceded by M, namely: P ← P₂ ← P₃ ← ... ← M, with infinitely many physical events in the “…”.

This scenario requires the possibility of an infinite sequence of causal means, contrary to causal finitism, and hence is unacceptable to me. But those who are less worried about infinite chains of causes should take this option seriously. Note that this option is reminiscent of Kant’s view on which our noumenal selves collectively cause the physical universe as a whole.

Option II: Physical-nonphysical-physical chaining: Here, the physical event P causes E by having a mental event as an intermediate cause. This option exploits a loophole in the closure principle as it is normally formulated: nothing in the closure principle says that the physical cause can’t operate by means of a nonphysical intermediary. Granted, that’s not how we normally think of physical causes as operating. But there is nothing incoherent about the story.

Option III: Physical parts of larger events: A physical event E is caused by a physical event P, and the physical event P is itself a part of a larger event M which is only partly physical. One might object that in this case it’s only P and not the larger event that counts as the cause. But that’s not right. If someone dies in the battle of Borodino, then at least three causes of death can be given: a shot being fired, the battle of Borodino, and the War of 1812. The shot is a part of the battle, and the battle is a part of the war. One particular way to have Option III is this: a quale Q is constituted by two components, a brain state B (say, a state of the visual cortex) and a soul state S of paying attention to the brain system that exhibits B, with B being the causally efficacious part of the Q. So a physical event—say, an agent’s making an exclamation at what they saw—counts as caused by the physical event B and the event Q which is not physical, or at least not completely physical.

One might object, however, that by “nonphysical”, one means entirely nonphysical, so Q’s having a nonphysical part S does not make Q nonphysical. If so, then we have one last option.

Option IV: Some or all physical causes cause their effects by having a nonphysical part that causes the event. That nonphysical part could, for instance, be an Aristotelian accidental or substantial form. Thus, here a physical event E is caused by a physical event by means of its nonphysical part M.

What if one objects that “physical” and “nonphysical” denote things that are purely physical and nonphysical, and neither can have a part that is the other? In that case, we have two difficulties. First, the closure principle is now stronger: it requires that a physical event that has a cause always has a purely physical cause. And we have a serious gap at the end of the argument. From closure at most we can conclude that a physical event doesn’t have a purely nonphysical cause. But what if it has a partly physical and partly nonphysical cause? That would be enough to contradict physicalism.

Forwards causal closure and dualist theories of perception

A standard dualist theory of perception goes like this:

1. You sense stuff physically, the data goes to the brain, the brain processes the data, and out of the processed data produces qualia.

There is a lot of discussion of the “causal closure” of the physical. What people generally mean by this is that the physical is causally backwards-closed: the cause of a physical thing is itself physical. This is a controversial doctrine, not least because it seems to imply that some physical things are uncaused. But what doesn’t get discussed much is a more plausible doctrine we might call the forwards causal closure of the physical: physical causes only have physical effects. Forwards causal closure of the physical is, I think, a very plausible candidate for a conceptual truth. The physical isn’t spooky—and it is spooky to have the power of producing something spooky. (One could leave this at this conceptual argument, or one could add the scholastic maxim that one cannot cause what one does not in some sense have.)

By forwards closure, on the standard dualist theory, the brain is not a physical thing. This is a problem. It is supposed to be one of the advantages of the standard dualist theory that it is compatible with property dualism on which people are physical but have non-physical properties. But if the brain is not physical, there is no hope for people to be physical! Personally, I don’t mind losing property dualism, but it sure sounds absurd to hold that the brain is not physical.

Recently, I have been thinking about a non-causal dualist theory that goes like this:

2. You sense stuff physically, the data goes to the brain, the brain processes the data, and the soul “observes” the brain’s processed data. (Or, perhaps more precisely, the person "feels" the neural data through the soul.)

To expand on this, what makes one feel pain is not the existence of a pain quale, but a sui generis “observation” relation between the soul and the brain’s processed data. This observation relation is not caused by the data, but takes place whether there is data there or not (if there isn’t, we have a perceptual blank slate). The soul is not changed intrinsically by the data: the “observation” of a particular datum—say, a datum representing a sharp pain in a toe—is an extrinsic feature of the soul. Note that unlike the standard theory, this up-front requires substance dualism of some sort, since the observing entity is not physical given the sui generis nature of the “observation” relation.

The non-causal dualist theory allows one to maintain forwards closure of the physical and the physicality of the brain. For the brain doesn’t cause a non-physical effect. The brain simply gets “observed”.

It is however possible that the soul causes an effect in the brain—for instance, the “observation” relation may trigger quantum collapse. Thus, the theory may violate backwards closure. And that’s fine by me. Backwards closure does not follow conceptually from the concept of the physical—a physical thing doesn’t become spooky for having a spooky cause.

There is a difficulty here, however. Suppose that the soul acts on the “observed” data, say by causing one to say “You stepped on my foot.” Wouldn’t we want to say that the brain data correlated with the pain caused one to say “You stepped on my foot”?

I think this temptation is resistable. Ridiculously oversimplifying, we can imagine that the soul has a conditional causal power to cause an utterance of “You stepped on my foot” under the condition of “observing” a certain kind of pain-correlated neural state. And while it is tempting to say that the satisfied conditions of a conditional causal power cause the causal power to go off, we need not say that. We can, simply, say that the causal power goes off, and the cause is not the condition, but the thing that has the causal power, in this case the soul.

On this story, if you step on my foot, you don’t cause me to say “You stepped on my foot”, though you do cause the condition of my conditional causal power to say so. We might say that in an extended sense there is a “causal explanation” of my utterance in terms of your stepping, and your stepping is “causally prior” to my utterance, even though this causal explanation is not itself an instance of causation simpliciter. If so, then all the stuff I say in my infinity book on causation should get translated into the language of causal explanation or causal priority. Or we can just say that there is a broad and a narrow sense of “cause”, and in the broad sense you cause me to speak and in the narrow you do not.

I think there is a very good theological reason to think this makes sense. For we shouldn’t say that our actions cause God to act. The idea of causing God to do anything seems directly contrary to divine transcendence. God is beyond our causal scope! Just as by forwards closure a physical thing cannot cause a spiritual effect, so too by transcendence a created thing cannot cause a divine effect. Yet, of course, our actions explain God’s actions. God answers prayers, rewards the just and punishes the unrepentant wicked. There is, thus, some sort of quasi-causal explanatory relation here that can be used just as much for non-causal dualist perception.

Nitpicking about the causal exclusion argument

Exclusion arguments against dualism, and sometimes against nonreductive physicalism, go something like this.

1. Every physical effect has a sufficient microphysical cause.

2. Some microphysical effects have non-overdetermined mental causes.

3. If an event E has two distinct causes A and B, with A sufficient, it is overdetermined.

4. So, some mental causes are identical to microphysical causes.

But (3) is just false as it stands. It neglects such cases of non-overdetermining distinct causes A and B as:

5. A is a sufficient cause of E and B is a proper part of A, or vice versa. (Example: E=window breaking; A=rock hitting window; B=front three quarters of rock hitting window.)

6. A is a sufficient cause of B and B is a sufficient cause of E, or vice versa, with these instances of sufficient causation being transitive. (Example: E=window breaking; A=Jones throwing rock at window; B=rock impacting window.)

7. B is an insufficient cause of A and A is a sufficient cause of B, with these instances of causation being transitive. (Example: E=window breaking; B=Jones throwing rock in general direction of window; A=rock impacting window.)

8. A and B are distinct fine-grained events which correspond to one coarse-grained event.

To take care of (6) and (7), we could replace “cause” with “immediate cause” in the argument. This would require the rejection of causation by a dense sequence of causes (e.g., the state of a Newtonian system at 3 pm is caused by its state at 2:30 pm, its state at 2:45 pm, at 2:52.5 pm, and so on, with no “immediate” cause). I defend such a rejection in my infinity book. But the price of taking on board the arguments in my infinity book is that one then has very good reason to accept the Kalaam argument, and hence to deny (1) (since the first physical state will then have a divine, and hence non-microphysical, cause).

We could take care of (5) and (8) by replacing “distinct” with “non-overlapping” in (3). But then the conclusion of the argument becomes much weaker, namely that some mental causes overlap microphysical causes. And that’s something that both the nonreductive physicalist and hylomorphic dualist can accept for different reasons: the nonreductive physicalist may hold that mental causes totally overlap with microphysical causes; the hylomorphist will say that the form is a part of both the mental cause and of the microphysical cause. Maybe we still have an argument against substance dualism, though.

Another way out of the closure argument

Consider this standard closure of the physical argument for physicalism (Papineau gives one very close to this):

1. Our conscious states have physical effects.

2. All physical effects are fully caused by physical causes.

3. There is (typically) no overdetermination.

4. So, our conscious states are (at least typically) physical.

Many dualists question (2), and epiphenomenalists question (1). But there is another move that seems to me to be promising.

When we say that our conscious states have physical effects, we don’t mean that our conscious states are the full causes of physical effects. Descartes himself would say that the movements of the particles in the pineal gland are partly caused by the conscious choice and partly caused by the prior state of the particles.

In other words, (1) just tells us that our conscious states are partial causes of physical effects. Given this, what (1)–(3) license us in concluding is only:

5. Our conscious states are (at least typically) parts of physical causes.

But to conclude from (5) that our conscious states are physical, it seems we need some premise like:

6. All the parts of physical things are physical.

But (6) is worth questioning. Note first that it is easier to find false than true cases of principles like:

7. All the parts of Fs are Fs

(E.g., electrons are parts of red things, but electrons aren’t red.) So why think (6) is true?

So, it seems that (6) needs some argument.

And in fact there are serious metaphysical views on which (6) is false. Consider, for instance, bundle theory: substances are bundles of properties. Well, rocks are physical objects, but a part of the bundle that makes up a rock will be the abstract entity of rockiness. But abstract entities aren’t physical.

Or take a reading (perhaps a misreading) of Leibniz on which physical objects are constituted by non-physical monads, and suppose that constituents count as parts.

Or, most promisingly, take Aristotle’s view on which all physical objects have form. Form is immaterial, and plausibly non-physical. Hylomorphism thus escapes the closure argument.

More generally, for all we know, the fundamental structure of reality is such that physically fundamental things are not ontologically fundamental but themselves have parts that are not physical.

The traveling minds interpretation of indeterministic theories

I'm going to start by offering a simple way—likely not original, but even if so, not very widely discussed—of turning an indeterministic physical theory into a deterministic physical theory with an indeterministic dualist metaphysics. While I do not claim, and indeed rather doubt, that the result correctly describes our world, the availability of this theory has some rather interesting implications for the mind-body and free will and determinism debates.

Start with any indeterministic theory that we can diagram as a branching structure. The first diagram illustrates such a theory. The fat red line is how things go. The thin black dotted lines are how things might have gone but didn't. At each node, things might go one way or another, and presumably the theory specifies the transition probabilities—the chances of going into the different branches. The distinction between the selected branches and the unselected branches is that between the actual and the merely possible.

The Everett many-worlds interpretation of Quantum Mechanics then provides us with a way of making an indeterministic theory deterministic. We simply suppose that all the branches are selected. When we get to a node, the world splits, and so do we its observers. All the lines are now fat and red: they are all taken. There are some rather serious probabilistic problems with the Everett interpretation—it works best if the probabilities of each branch coming out of a node are equal, but in general we would not expect this to be true. Also, there are serious ethics problems, since we don't get to affect the overall lot of humankind—no matter which branch we ourselves take, there will be misery on some equally real branches and happiness on others, and we can do nothing about that.

To solve the probabilistic problems, people introduce the many-minds interpretation of the many-worlds interpretation. Each person has infinitely many minds. When we get to a branch point, each mind indeterministically "chooses" (i.e., is selected to) an outgoing branch according to the probabilities in the physics. Since there are infinitely many of these minds, at least in the case where there are finitely many branches coming out of a node we will expect each outgoing branch to get infinitely many of the minds going along it. So we're still splitting, and we still have the ethics problems since we don't get to affect the overall lot of humankind—or even of ourselves (no matter which branch we go on, infinitely many of our minds will be miserable and infinitely many will be happy).

But now I want to offer a traveling minds interpretation of the indeterministic theory. On the physical side, this interpretation is just like the many-worlds interpretation. It is a dualist interpretation like the many-minds one: we each have a non-physical mind. But there is only one mind per person, as per common sense, and minds never split. Moreover our minds are all stuck together: they always travel together. When we come to a branching point, the physical world splits just as on the many-worlds interpretation. But the minds now collectively travel together on one of the outgoing branches, with the probability of the minds taking a branch being given by the indeterministic theory.

In the diagram, the red lines indicate physical reality. So unlike in the original indeterministic theory, and like in the many worlds interpretation, all the branches are physically real. But the thick red lines and the filled-in nodes, indicate the observed branches, the ones with the minds. (Of course, if God exists, he observes all the branches, but here I am only talking of the embodied observers.) On the many-worlds interpretation, all the relevant branches were not only physically real, but also observed. Presumably, many of the unobserved branches have zombies: they have an underlying physical reality that is very much like the physical reality we observe, but there are no minds.

The traveling minds interpretation solves the probability problems. The minds can travel precisely according to the probabilities given by the physics. Traveling minds as generated in the above way will have exactly the same empirical predictions as the original indeterministic theory. (In particular, one can build traveling minds from a Copenhagen-style consciousness-causes-collapse interpretation of Quantum Mechanics, or a GRW-style interpretation.)

Traveling Minds helps a lot with the ethics problem that many-worlds and many-minds faced. For although physical reality is deterministically set, it is not set which part of physical reality is connected with the minds. We cannot affect what physical reality is like, but we can affect which part of physical reality we collectively experience. And that's all we need. Note that "we" here will include all the conscious animals as well: their minds are traveling as well. In fact, as a Thomist, I would be inclined to more generally make this a "traveling forms" theory. Thus the unselected branches not only have zombies, but they have physical arrangements like those of a tree, but it's not a tree but just an arrangement of fields or particles because it lacks metaphysical form. But in the following I won't assume this enhanced version of the theory.

Now while I don't endorse this theory or interpretation—I don't know if it can be made to fit with hylomorphic metaphysics—I do want to note that it opens an area of logical space that I think a lot of people haven't thought about.

Traveling minds is an epiphenomenalist theory (no mind-to-physics causation) with physical determinism, and is as compatible with the causal closure of the physical as any physicalist theory (it may be that physicalist theories themselves require a First Cause; if so, then so will the traveling minds theory). Nonetheless, it is a theory that allows for fairly robust alternate possibilities freedom. While you cannot affect what physical reality is like, you can affect what part of physical reality we collectively inhabit, and that's almost as good. We have a solution to the mind-to-world causation problem for dualism (not that I think it's an important problem metaphysically speaking).

I expect that I and other philosophers have incautiously said many things about things like epiphenomenalism, determinism and causal closure that the traveling minds theory provides a counterexample to. For instance, while traveling minds is a version of epiphenomenalism, it is largely untouched by the standard objections to epiphenomenalism. For instance, one of the major arguments against epiphenomenalism is that if minds make no causal difference, then I have no reason to think you have a mind, since your mind makes no impact on my observations. But this argument fails because it assumes incorrectly that the only way for your mind to make an impact on my observations is by affecting physical reality. But your mind can also make an impact on my observations by leaving physical reality unchanged, and simply affecting which part of physical reality we are all collectively hooked up to.

Causal closure of the physical

If causal closure of the physical holds, then there are uncaused physical states of affairs. Thus, at least one of the following two theses is true:

1. Some physical states of affairs have a non-physical cause.
2. Some physical states of affairs have no cause.

Now, what I don't see is why (2) should be in any way preferable to (1). For instance, to the extent that some physical state of affairs lacks a physical cause, science has nothing to tell us about the explanation of this state of affairs. For all that science cares, that state might have a non-physical explanation or it might have no explanation. Allowing the first option need no more impede the progress of science than allowing the second. Granted, the first option may let one prematurely say when faced with difficulties that some state of affairs for which a physical cause has not been found has a non-physical cause. But the second option lets one say, equally prematurely, that it has no cause.

Imagine two worlds. In w₁, there are non-physical causes for all the physically uncaused physical states of affairs. In w₂, there are no causes for any of the physically uncaused physical states of affairs. Moreover, the physical parts of w₁ and w₂ are exactly alike, and match our observations. Is there very good reason to prefer w₂ to w₁ as a hypothesis accounting for our observations? Well, maybe sometimes: it depends on how weird the non-physical stuff in w₁ is. But in general, no. Roughly, what w₂ gains in parsimony it may lose in explanatory value.

So we do not have very good reason to believe (2) and deny (1). And (1) has a serious advantage over (2): unlike (2), (1) is compatible with our PSR-ish intuitions.