Galen Strawson on Zombies and Whether 'Physical' is a Natural Kind Term

1. What is a zombie? 

You will have gathered that a zombie is a creature of philosophical fiction conjured up to render graphic a philosophical issue and to throw certain questions in the philosophy of mind into relief.    A zombie is a living being that is physically and behaviorally exactly like a living human being except that it lacks (phenomenal) consciousness.  Cut a zombie open, and you find exactly what you would find were you to cut a human being open. And in terms of linguistic and nonlinguistic behavior, there is no way to tell a human being from a zombie. (So don't think of something sleepy, or drugged, or comatose or Halloweenish.)  When a zombie sees a tree, what is going on in the zombie's brain is a 'visual' computational process, but the zombie lacks what a French philosopher would call interiority. There is no irreducible subjectivity, no qualitative feel to the 'visual' processing; there is nothing it is like for a zombie to see a female zombie or to desire her. (What's it like to be a horny zombie? There is nothing it is like to be a horny zombie.  Indeed, there is nothing it is like to be a zombie, period.) 

2. Where do zombies come from?  

Zombies surface within the context of discussions of physicalism. Physicalism is an ontological doctrine, a doctrine about what ultimately exists,  what exists in the most fundamental sense of 'exists.'  The physicalist is committed to the proposition that everything, or at least everything concrete, is either physical or determined by the physical. To be a bit more precise, physicalism is usefully viewed as the conjunction of an 'inventory thesis' which specifies physicalistically admissible individuals and a 'determination thesis' which specifies physicalistically admissible properties. What the inventory thesis says, at a first approximation, is that every concretum is either a physical item or composed of physical items. As for the determination thesis, what it says is that physical property-instantiations determine all other property-instantiations; equivalently, every nonphysical property-instantiation supervenes on physical property-instantiations. This implies that all mental facts supervene upon physical facts.  So if a being is conscious, then this fact about it supervenes upon, is determined by, its physical properties.  This implies that there cannot be two beings, indiscernible with respect to all physical properties, such that the one is conscious while the other is not.  This in turn rules out the possibility of zombies.  For, if physicalism is true, once the physical properties are fixed, the mental properties are also automatically fixed.

3. What useful work do zombies do? 

If zombies are metaphysically (broadly logically) possible, then physicalism is false.  That's their job: to serve as counterexamples to physicalism.  For if zombies are possible, then it is not the case that every nonphysical property-instantiation supervenes upon a physical property-instantiation: a zombie has all the same physical properties as its indiscernible non-zombie twin, but is not conscious.  The possibility of zombies implies that consciousness is non-supervenient, something in addition to a being's physical makeup.  So one anti-physicalist argument goes like this:

1. If physicalism is true, then every nonphysical property-instantiation supervenes upon a physical property-instantiation. 
2. If zombies are possible, then it is not the case that every nonphysical property-instantiation supervenes upon a physical property-instantiation.
3. Zombies are possible.
Therefore
4. Physicalism is not true.

This is a valid argument the soundness of which rides on premise (3).  Here is where the fight will come.  Without questioning the validity of the argument the physicalist will run the argument in reverse.  He will deny the conclusion and then deny (3).  In effect, he will argue from (1) & (2) & (~4)  to (~3).  He will deny the very possibility of zombies.  He will insist that anything that behaves just like a conscious person and has the 'innards' of a conscious person JUST IS a conscious person.

Now I find that absurd: it is a denial of that subjectivity which is properly accessed only via the irreducible first-person singular point of view.  Nevertheless, I will have a devil of a time budging my materialist-functionalist interlocutor.  Materialists are objectivists: they think that anything that is not objectively accessible in the third-person way just isn't there at all, or it if is 'there,' is not to be taken seriously.

Can one support (3) in a manner so compelling as to convince the recalcitrant materialist?  After all, (3) is not self-evident.  If it were self-evident, then we would have a 'knock-down' argument against physicalism.  But there are few if any  'knock-down' (absolutely compelling)  arguments in philosophy. 

Now zombies are certainly conceivable.  But it is not clear whether conceivability entails metaphysical (broadly logical) possibility, which is in play in (3).    So it is not clear whether the conceivability of zombies is a compelling  reason to reject physicalism.  The question of the relation between conceivability and possibility is a difficult one.  There is some discussion of this in the conceivability category.

Now here is what Galen Strawson has to say:

4. Strawson on Zombies.

It is, finally, a mistake to think that we can know that ‘zombies’ could exist—where zombies are understood to be creatures that have no experiential properties although they are perfect physical duplicates (PPDs) of currently experiencing human beings like you and me.

The argument that PPD-zombies could exist proceeds from two premisses—[1] it is conceivable that PPD-zombies exist, [2] if something is conceivable, then it is possible. It is plainly valid, and (unlike many) I have no insuperable problem with [2]. The problem is that we can't know [1] to be true, and have no reason to think it is. To be a materialist is, precisely, to hold that it is false, and while materialism cannot be known to be true, it cannot be refuted a priori—as it could be if [1] were established. ‘Physical’, recall, is a natural kind term, and since we know that there is much that we do not know about the nature of the physical, we cannot claim to  know that an experienceless PPD of a currently experiencing human being is conceivable, and could possibly (or ‘in some possible world’) exist.

This is just blatant question-begging on Strawson's part.  We can't know that it is conceivable that zombies exist?!  That zombies are conceivable is a very weak claim, and of course we can know it to be true, just by conceiving a zombie, whence it follows that we have excellent reason to think it is true.  Strawson simply begs the question by assuming that materialism is true.  He also begs the question by claiming that materialism cannot be refuted a priori.   If you grant [2], as Strawson does, then what we have is an a priori refutation of materialism.

Strawson tells us that 'physical' is a natural kind term.  What a strange idea! 'Water,' 'gold, 'tiger' are uncontroversial natural kind terms.  They succeed in referring to what they were introduced to refer to despite our knowledge or ignorance of the nature of what they refer to.  The ancient Greeks thought water was an element; Dalton held it to be HO; we take it to be H₂O.  Water turned out to be a lot different than we thought, without prejudice to the reference of 'water.' So if 'physical' is a natural kind term, then it too can refer to things very different in nature than what we might have supposed.  And so Strawson thinks that 'physical' can refer to what is irreducibly mental or experiential in whole or in part.  In fact, Strawson allows that the physical -- that which physics studies -- could be wholly mental.

I don't know what this means.  Perhaps Vlastimil can explain it to me.

Comments

[Elliott]

Bill,

Thanks for your series of posts on this topic. I agree with you that (a) consciousness is not an illusion, (b) we know what consciousness is in a direct and unmistakable way, and (c) consciousness does not supervene on the physical.

Regarding the passage from Strawson, it appears he is avoiding the heart of the problem with something like a definist fallacy. He seems to define the term 'physical' such that everything is physical, including what many consider themselves to reasonably take to be mental. But this move misses the main point. This move also stretches the extension of 'physical' so far that the term loses its meaning.

[Bill Vallicella]

Thanks for reading, Elliot.

I am still trying to figure out what game Strawson is playing.

[Elliott]

>>and since we know that there is much that we do not know about the nature of the physical, we cannot claim to know that an experienceless PPD of a currently experiencing human being is conceivable ...<<

In this line of reasoning, he seems to assume the following: "If we know we lack knowledge about the physical, then we can't claim to know that a zombie is conceivable."

In other words, the assertion "we can't claim knowledge that zombies are conceivable" is taken as a necessary condition of our lack of knowledge about the physical. But this point apparently presupposes physicalism, or at least it presupposes that ignorance of certain relevant physical facts is sufficient to prevent us from claiming knowledge that a zombie is conceivable.

But, it seems, this point begs the question against an ontological idealist who holds that zombies are conceivable. If everything were mental, as an ontological idealist would hold, then zombies would be mental items too, and our ability to conceive of them would correspond to the metaphysics and epistemology of idealism.

The point also begs the question against a substance dualist who holds that zombies are presently conceivable despite the physical-fact knowledge gap.

If this is his assumption, consider its contrapositive equivalent: "If we can claim to know that a zombie is conceivable, then it's not the case that we know we lack knowledge about the physical." This doesn't make much sense. If one can claim to know that a zombie is conceivable, why would it follow that we are ignorant of our ignorance of the physical?

[Elliott]

It seems to me another problem with Strawson's approach is that (a) he assumes we're wholly physical beings -- as if we've discovered some evidence that shows this to be true, but (b) he claims we face this large gap in knowledge of the physical world so that we just don't know how it is the case we are wholly physical beings.

Curiously, however, he doesn't appear to say exactly what it is we know regarding (a) and (b). He merely asserts that we know.

[Vlastimil Vohánka]

Bill,

I've been interested in physicalism conceived more strongly, i.e. as consisting just in the inventory thesis. Not as consisting in the inventory plus the determination theses. So I don't have much to say to this discussion.

Does Strawson say how he uses 'conceivable'? Perhaps his usage is more loaded than yours.