Rethinking Physicalism

Susan SchneiderThe University of Connecticut

Background

In a previous book, I explored the computational paradigm in cognitive science.

I devised a new version of one computational approach to the the brain.

Digging Deeper

That book wasn’t in metaphysics, but as I turned to metaphysics, I began to see the computational approach as only one layer of the story about the metaphysical nature of mind.

For instance, it could turn out that even if everyone agreed on a certain computational approach to the brain, substance dualism is correct.

There could be philosophical reasons why the mind is not the brain.

I’m not saying that there are immaterial substances “outside” of spacetime.

But there is more to the metaphysical nature of mind than many current philosophers of psychology envision. (See my papers at my site in Nous, PPR, and Phil. Studies.)

Computationalism, even if correct about the brain, is only the beginning of the philosophical story…

The Mind-Body Problem: Rethinking the Solution Space (the next book)

The Mind-Body Problem: how the mind, and its thoughts, relate to the world science investigates, and particularly, to fundamental physics.

Computationalists tend to be “non-reductive physicalists”:

Nonreductive Physicalism: i. Mental properties (i.e., features) do not reduce

to physical ones, but they depend on physical properties.

ii. Physicalism. The mind is physical, and all other things (or substances) are as well.

Previously I urged this position is false.

(PI) Any commitment to property irreducibility is incompatible with the view that the mind is a physical thing.

Property irreducibility leads to a form of substance dualism, but not a Cartesian one.

A similar problem arises for certain other major positions on the mind-body problem.

Today, I will illustrate (PI) in one context -- the context of the debate on consciousness.

You’ll see how the worries extend to non-reductive physicalism.

The Hard Problem of Consciousness (David Chalmers)

As cognitive science underscores, when we deliberate, hear music, see the rich hues of a sunset, and so on, there is information processing going on in the brain.

But above and beyond the manipulation of data, there is a subjective side - there is a felt quality to our experience (“qualia”).

The Hard Problem, cont.,

Chalmers singing the Zombie Blues.

The subjective life of the brain is perplexing: why is it that there is consciousness associated with our information processing?

Why aren’t we simply computational devices without any sensation at all?

Why aren’t we “experience zombies”?

The Hard Problem, cont.,

The hard problem asks: why do we need to have any experience at all?

Why couldn’t a robot, lacking consciousness, have performed the same tasks just as well?

Why doesn’t all our information processing happen “in the dark”?

Chalmers’ View The hard problem is a philosophers’ problem,

because it doesn’t seem to have a scientific answer.

E.g., we could develop a complete theory of vision, and still not show why seeing a sunset feels the way it does.

But this does not mean that scientific work on consciousness is unimportant.

“Easy Problems” The Hard Problem is contrasted with “Easy

Problems” that have eventual scientific answers.

Easy Problems: Ability to discriminate, categorize and react to stimuli, the mechanism of attention, the difference between wakefulness and sleep.

Of course these are hard problems; but Chalmers calls them “Easy Problems” to underscore a contrast with the main problem of consciousness, which he thinks will not have a purely scientific solution.

Chalmers’ Answer to the Hard Problem

Chalmers thinks consciousness is a fundamental building block of the universe.

So suppose consciousness is basic, alongside the physical properties a completed physics identifies. (“Property dualism”)

We normally think view does not lead to substance dualism.

For there are well-known property dualists who hold that while mental and physical properties are distinct, all substances are physical.

(SP) and (PD)

That is, they hold both:

(SP) Substance physicalism: all substances are physical.

And,

(PD) Property dualism: mental and physical properties are distinct.

(Non-reductive physicalism and emergentism hold these tenets too.)

Task Setting

Today: insofar as a leading theory of substance is in force, property dualism is incompatible with the view that the mind (or any bearer of consciousness, even the brain) is physical.

“The Mind Problem.”

Targets:

Qualia based property dualism (today)

Non-reductive physicalism

Emergentism

Extended mind scenarios

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Substance Physicalism

Philosophers of mind generally view the question of the nature of substance as being settled in favor of the physicalist.

Dualism about properties, in contrast, is regarded as being a live option.

“…the fact is that substance dualism has played a very small role in contemporary discussions of philosophy of mind….Dualism is no longer a dualism of two sorts of substances; it is now a dualism of two sorts of properties, mental and physical” (Jaegwon Kim, Philosophy of Mind, 2006, p. 51).

The debate over substance dualism shouldn’t be over.

Quick Point About Tropes Tropes are properties that aren’t

repeatables, the way universals are.

E.g., the three espresso shots do not literally share the very same properties.

Tropes are currently an influential alternative to D.M. Armstrong’s universals.

If properties are tropes the property dualist cannot hold that all particulars are physical.

Reality contains irreducibly mental tropes. Mental particulars are in the property dualist’s basic ontology.

Reply Retort: tropes aren’t substances.

My reply: we’re going there too, but this alone is significant.

The inventory of particulars consists in more than that which physics delivers up!

The Mind Problem

Question: How are we to understand the relation between a thing (e.g., the brain) and its properties -- e.g., the experience of seeing the sunrise?

We are asking about the nature of substance.

Substances are, roughly, objects, where such could be physical or nonphysical.

The Mind Problem: on both of the leading conceptions of substance, given a commitment to property irreducibility, substance physicalism (SP) is false.

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The Bundle and Substratum Theories of Substance

Both approaches are close cousins.

Substances are not basic; instead, the category of substance reduces to (inter alia) properties.

The properties can be tropes or universals.

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The Bundle Theory of Substance

Bundle Theory: substances are bundles of their properties.

Not every bundle of properties is an object.

So what unites bundles that are genuine substances?

Primitive ‘‘compresence’’, ‘‘co-instantiation’’, or ‘‘collocation.”

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The Substratum Theory The Substratum Theory: objects’ natures are not exhausted by their

properties – they have substrata as well.

Substratum: a core that bears properties but is not itself a property.

As our sensory access to objects is through their properties, substrata will seem rather mysterious.

Locke – something “I know not what” (An Essay Concerning Human Understanding,1689, II, xxiii, §2).

So why should we believe in them? Belief in substrata comes from appreciating deficiencies in the bundle theory.

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The Mind Problem for the Bundle View

When properties are construed as being either universals or tropes, given (PI), (SP) is false.

Focusing on the bundle theory:

“Suppose you are walking along a beach. As you experience the rich hues of the ocean and sky, and feel the warmth of the sun on your face, why is the mind—i.e., the substance that has the experiential properties—a physical thing? Why is it that a physical bundle instantiates the experiential properties, since... there would be a bundle that has irreducible phenomenal properties as constituents? … if you reject property dualism for the type identity theory, you will not find this matter compelling: the same substance has both kinds of features because mental properties just are physical ones. But we are assuming a property dualist conception; and on this conception there is a categorical divide between mental and physical properties, and when substances are bundles, it is

important to ask: Given that non-physical properties are constituents of the bundle, why would the bundle be physical?” (Phil. Studies, Vol. 157, Nu. 1, 2012).

The Mind Problem, cont., Why is the mind not a “hybrid” substance -- one that

consists in both physical and mental properties?

Or why are there not two “Cartesian” bundles instead: a physical one (the brain) and a non-physical one (the mind)?

(Disclaimer: Descartes was not a bundle theorist.)

Either way, we have substance dualism.

Can raise the problem for whatever you think the bearer of mental properties is (self, person, etc.).

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Objection: Hybrids are Physicalistically Kosher

Critic: So what? One can grant that substances are hybrid, insisting they are physical nonetheless. For a physical substance can have both mental and physical properties.

But notice that the present point is not that the substance has properties of both types; the point is that a hybrid substance is constituted by both types of properties.

A substance is not physically kosher if it contains a metaphysical constituent that is not.

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Objection 2: Naturalistic Substance Dualism

Objection 2. Hybrid substances are spatiotemporal, not immaterial, so they are physical. So this is not substance dualism.

Response. A substance dualist need not accept Descartes’ view that mental substances are immaterial, being unsuitable to have physical properties.

E.g., E.J. Lowe holds, with Descartes, that the self is distinct from its body. Yet Lowe’s view (in his words) “…does not insist either that the self is separable from anything bodily or that it is spatially unextended. It allows, that is, that the self may not be able to exist without a body and that it may be extended in space, thus possessing spatial properties such as shape, size, and spatial location.” (“Non-Cartesian Substance Dualism and the Problem of Mental Causation.” Erkenntnis, 65(1)).

Lowe’s Substance Dualism You may ask: why is Lowe’s self non-physical, given that, unlike Cartesian dualism, it bears physical properties?

Lowe’s self is non-physical because, according to Lowe, selves and their bodies have different persistence conditions -- the self can continue to exist even when the brain’s parts are gradually replaced.

While selves are part of the world that science investigates, they are non-physical. Naturalism without physicalism.

Lowe’s Substance Dualism, cont.

Objection. The property dualist is not saying the mind and brain have different persistence conditions.

Response. Aren’t they?

(1) Zombie Thought Experiment

Property dualism holds that mental properties nomologically supervene on physical ones. But there can be zombie worlds: a philosophical zombie is a system that is physically identical to a conscious being, but lacks that being’s conscious states.

Not like the picture.

Zombies have brains, but, ex hypothesi, they are incapable of having experience. Do zombies have minds?

I doubt the property dualist will want to say that they do: remember, for the property dualist, consciousness is the mark of the mental.

But now, consider: brains have different modal properties than minds do, for brains can exist even if they are incapable of having consciousness —or so the property dualist says.

Not so with minds. Brains do not have consciousness properties essentially; minds plausibly do.

But if the property dualist allows that minds and brains differ in this way, they cannot be identical.

(2) The Worldmaking God God is busy worldmaking.

What would he need to do to create physical objects?

Answer: God must set the fundamental physical properties, the compresence relation and (perhaps) spacetime.

Next question: what would God need to do to create minds?

(2) Minds and Brains as Distinct Substances

Property dualist answer: God must make sure consciousness is basic.

After all, for property dualism, if anything is to characterize the nature of mind, wouldn’t it be consciousness properties?

But no genuine substance physicalist can venture this answer. If God needs to add mental properties to the world to create minds, minds are not physical.

More Objections: (3) Qualia are non-essential.

Chalmers’ objection: qualia are not constitutive of any bundle. They are accidental properties of physical substances (the mind/brain).

So minds are physical.

My Reply The fundamental physical properties type individuate the fundamental

particles.

Yet Chalmers is saying qualia do not type individuate anything, being merely accidental properties of the mind/brain.

This isn’t how fundamental properties work in physics. Further:

“This is not to assume that every property is type individuative; it is just to say that it is odd that the property dualist is saying that mental properties are ontologically basic—otherwise the mind is not explainable—yet they do not type individuate the mind/brain. Only physical properties do. If this is the case then zombies should have minds. And God shouldn’t have to do anything extra to brains to add mentality to the world. But the property dualist would reject these claims. So: where is the argument for the view that phenomenal properties are not type individuative?” (Phil. Studies, vol. 157, nu. 1.)

Objection 4: Minds aren’t Ontologically Serious (Ned Block)

They are shorthand for talk of mental properties.

It is odd that a property dualist, of all people, would adopt such a deflationary view of minds.

But in any case, let us ask: on this view, what is the bearer of the mental properties? Persons? Selves? Here, the same issues arise: why isn’t the bundle that is the person or self non-physical?

Perhaps the property dualist would take a deflationary view of persons and selves as well, saying that brains are the bearers of the mental properties. But then if so, why are brains physical if they have fundamental qualia?

Further, notice that on the bundle theory substances are bundles of properties. The deflationary approach begs the question: why are minds not substances then?

Objection 5: Metaphysical Innocence

Anonymous reviewer: If the bundle theory is true, substance dualism is no big deal.

Substances are just bundles of properties. And the substance dualist already admits that experiential properties are non-physical.

“If property dualism leads to an innocent brand of substance dualism, the property dualist interested in (SP) can shrug: if that’s all substance dualism amounts to, so be it.”

My Response

Bundle theories are ontologies of universals or tropes. Still, minds are just as real as their metaphysical constituents.

So learning that property dualism is a substance dualist position is progress on the mind–body problem!

A Suggestion: “Naturalistic” Substance Dualism

Here’s what the property dualist can do.

Question: think about how a hybrid bundle (the mind) would relate to the physical bundle that underlies it.

How would that work?

Naturalistic Substance Dualism (“NSD”)

The naturalistic property dualist holds that to explain consciousness one must posit basic psychophysical laws.

Now, as per the bundle theory, the mental and physical properties figuring in the laws are constituents of the hybrid and physical bundles, respectively.

This leaves us with nomologically necessary relations of dependency between the mind and the brain.

Corresponding to each mind there is a brain, a complex physical substance ultimately made up of fundamental microphysical entities (e.g., strings).

The presence of the brain—that is, the presence of a physical substance in a highly sophisticated neural configuration—is nomologically sufficient for a mind.

Naturalistic Substance Dualism, cont.

Mental causation is a major problem with traditional substance dualisms.

If the mind is non-physical, it lacks a position in physical space. So how can it interact with physical substances?

But notice that this problem does not arise – hybrid substances are spatiotemporal.

Causation is no more problematic than it was under property dualism proper.

(Caveat: Mental causation is a mess for property dualism, but nothing is worse).

Naturalistic Substance Dualism, cont.

Assuming NSD does not introduce a form of substance causation—that is, assuming it maintains that causation is a relation among events—the problem of how mental substances enter into the causal nexus is the standard problem of how mental properties can be causal given that all the causal work appears to be done in the microphysical realm.

Now, the naturalistic property dualist holds that consciousness is where the brain is. It is not “outside” of spacetime.

So the mind (the non-physical bundle), while being distinct from the brain, spatiotemporally coincides with it.

Conclusion The textbook view that substance dualism is dead is dead wrong.

Property dualism is important, and it needs to reject substance physicalism.

Extensions:

Non-reductive physicalism is false because minds aren’t physical when mental properties are irreducible. (See my Nous paper at my site).

Suggests computationalism needs a better metaphysics of mind.

Challenges emergentism -- non-physical properties are said to emerge from a physical substance.

Challenges extended mind views that hold (PI).

So: current thinking on the mind-body problem needs radical revision: physicalism about substances, like physicalism about properties, is up for grabs.