Zombies Schmonceivability and the Mirroring Objection All EscapeRoutes

Zombies, Schmonceivability and the Mirroring Objection: All Escape-Routes Barred Doug Campbell Department of Philosophy

Background

Materialism • • P – a conjunction of the actually obtaining microphysical facts. T – a ‘totality operator’ (or ‘that’s all’ clause). PT – says that no facts obtain beyond those supervenient on P. Q – a conjunction of all actually obtaining facts, including the phenomenal facts. Materialism: • It is thesis □(PT→Q) – that any ‘PT-world’ must also be a ‘Q-world’ – that the phenomenal facts (and all other facts) supervene metaphysically on the bare microphysical facts – that ‘a minimal physical duplicate of the actual world is a duplicate simpliciter’

Materialism Minds and Qualia If materialism is true then God thereby automatically fixes all the actually obtaining facts, including the qualitative facts. (All the actually obtaining facts come ‘for free’ with PT. ) (Here we conveniently turn a blind eye to the fact that God’s existence is probably incompatible with materialism!) God fixes all the microphysical facts, and then says “that’s all”. I. e. , God makes PT true.

What it is like to be a normal person riding a mountain bike

What it is like to be a philosophical zombie riding a mountain bike (Except it is not even black. What is like to be a philosophical zombie matches what it is like to be in a dreamless sleep, or in a coma, or dead. )

What a philosophical zombie does not look like

What a philosophical zombie does look like

A Philosophical Zombie From the outside she appears to be a perfectly normal person. From a behavioral, psychological , or neurophysiological perspectives she is perfectly normal. But she has no inner mental life. She has no subjective experiences. There is “no one at home”. She will claim to be conscious, just like a normal person. But really, she isn’t.

Austere Conceivability • p is austerely conceivable iff p is free of any a priori detectable contradictions. – I. e. , p is austerely conceivable iff no one, no matter how highly rational they might be, could ever find a contradiction in p by a process of mere rational reflection. • Notation: ◇cp represents the claim that p is austerely conceivable. • Henceforth by ‘conceivable’ I will mean ‘austerely conceivable’ unless I explicitly say otherwise.

The principle that Conceivability Entails Possibility (CEP)

The zombie argument against materialism The conceivability of a zombie world (where PT is true but Q is not) CEP Logical truth The denial of materialism

The usual materialist responses Attack Z 1. Zombies are not austerely conceivable � � Attack Z 2: conceivability is not a reliable guide to possibility

Our response: the mirror argument The conceivability of a world where PT is true and Q is true too. CEP Logical truth Materialism

Why is M 3 a logical truth? • M 3 says, in effect, that if there is some PT world that is a Q world, then every PT world is a Q world. • This is true because of the meaning of the T operator. – A PT world is a world where all the facts supervene on the P facts. – Thus any two PT world must be exactly alike. – Hence if some PT world is a Q world, then every PT world will be a Q world (just as M 3 says).

Chalmers dilemma, short version So it seems he must deny M 1. And he can’t deny M 2 without undermining CEP, which he relies on to justify M 2 But he can’t deny M 3, since it is a tautology Chalmers can’t accept M 4, since it contradicts his own conclusion. Hence he must deny M 1, M 2, or M 3

Why Chalmers can’t easily deny M 1 • In denying M 1, he would be saying PT∧Q is inconceivable. • That is, he would be saying that PT∧Q entails some a priori detectable contradiction. • Either he can demonstrate the contradiction, or not.

Suppose he can demonstrate a contradiction in PT∧Q • Then he can refute materialism using the following argument, the “Anti-materialist’s Inconceivability argument” (AIA): PT∧Q is inconceivable Inconceivability entails impossibility Logical truth The denial of materialism The AIA would make the zombie argument logically redundant. He wouldn’t need the zombie argument to refute materialism, because he could use the AIA instead.

Suppose he can’t demonstrate a contradiction in PT∧Q • Then he is claiming that M 1 is false (and thus that PT∧Q is contradictory) even though he can’t show us the contradiction in question. • But this allows the materialist to turn the tables on Chalmers. – The materialist can pull the same trick, by claiming that Chalmers’ premise, Z 1 is false (i. e. , that PT∧¬Q is contradictory). – The materialist needn’t feel any need to demonstrate the contradiction in question. – Sauce for the materialist’s goose is sauce for Chalmers’ gander.

The situation is symmetrical

Chalmers’ response • “It may be prima facie negatively conceivable that materialism is true about consciousness, but it is not obviously conceivable in any stronger sense. Many people have noted that it is very hard to imagine that consciousness is a physical process. I do not think that this unimaginability is so obvious that it should be used as a premise in an argument against materialism, but likewise the imaginability claim cannot be used as a premise either. ” (Chalmers, 2010, p. 180)

Chalmers’ response (recent email) (He doesn’t do capitals in emails!) • i suppose i think our initial intuitions favor the inconceivability claim, so based on those it's at least 75% plausible, say. that does allow me to assign 75% credence to the falsity of materialism even without bringing in the zombie argument. however, (i) this argument is dialectically weak as the premise is so easy to deny, and (ii) the zombie argument allows a much stronger conclusion -- since i think it's much more than 75% plausible that zombies are conceivable, leading to much greater credence that materialism is false. for both of these reasons ZA isn't redundant.

Chalmers’ response ✓ ✗ ✓ ✓ ✓

In our new article we attempt to systematically examine all Chalmers’ options, including the option he actually endorses, and show that all carry great costs.

Chalmers’ options • The Austere Route. He grants that Z 1, Z 2, Z 3⊢Z 4 is indeed an accurate formalization of the zombie argument. – The Anti-M 2 Route. As for the Austere Route, and Chalmers opts to deny M 2. – The Pro-M 2 Route. As for the Austere Route, and Chalmers opts to accept M 2. • The Constitutive Route. As for the Pro-M 2 Route, and Chalmers holds that S+AIA doesn’t make the zombie argument logically redundant because S+AIA is partly constituted by the zombie argument. • The Non-Constitutive Route. As for the Pro-M 2 Route, and Chalmers accepts that S+AIA is not partly constituted by the zombie argument. – The Stopgap Route. As for the Non-Constitutive Route, and Chalmers holds that S+AIA has not yet made the zombie argument redundant because S hasn’t yet been found. (The zombie argument is temporarily valuable, as a ‘stopgap’, while the anti -materialist is still searching for S. ) – The Demonstrative Route. As for the Non-Constitutive Route, and Chalmers holds that S has been found. (S can be ‘demonstrated’. ) • The Non-Austere Route. He rejects this formalization of the zombie argument, on the basis that the notion of ‘conceivability’ operative within the zombie argument is not austere conceivability.

The Austere Route ✓ ✓ ✓ ✗

The Anti-M 2 Route ✓ ✓ ✓ ✗

The Anti-M 2 Route • By denying M 2, Chalmers would be holding that PT∧Q is a counterexample to CEP. • In order to deny M 2 without simultaneously undermining Z 1, he would need to hold that CEP has a restriction clause that excludes PT∧Q, but not PT∧¬Q, from its scope.

CEP’s restriction clauses • R 1: CEP can be used to derive ◇p from ◇cp only if p doesn’t contain any rigid designator, R, such that (i) R refers opaquely (i. e. , by describing an accidental property of its referent) and (ii) whether p is possible or impossible depends on R’s referent. • E. g. , CEP should not be applies to (2), which is conceivable but impossible: (1) Water is not H 2 O. • But R 1 is of no use to Chalmers. If it excluded PT∧Q from CEP’s scope it would almost certainly exclude PT∧¬ Q, too.

CEP’s restriction clauses • R 2: CEP can be used to derive ◇p from ◇cp only if p doesn’t make a mathematical or logical claim that, if false, could be refuted only by completing a supertask. • E. g. , CEP should not be applied to (2), which is (probably) conceivable but impossible: (2) Goldbach’s conjecture is false—i. e. , there does exist some even number greater than two that is not the sum of two primes. • But R 2 is of no use to Chalmers, since PT∧Q isn’t such a logical or mathematical claim.

CEP’s restriction clauses • R 3: CEP can be used to derive ◇p from ◇cp only if p doesn’t contain any phenomenal concept, D, such that whether p is possible or impossible depends on which physical or functional state D refers to. [CONTROVERSIAL] • E. g. , CEP should not be applied to PT∧¬Q • But R 3 is of no use to Chalmers, since it undermines Z 2 as well as M 2.

So, the Anti-M 2 Route carries the following prohibitive cost: • Cost A: acknowledging that the zombie argument’s proponent has a major unmet burden—namely, that of demonstrating the existence of a new category of non-Kripkean conceivable impossibilities (a category of which PT∧Q but not PT∧¬Q is a member).

The Pro-M 2 Route ✓ ✓ ✓ ✗

The Constitutive Route ✓ ✓ ✓ ✗ 1. PT∧Q Assumption 2. PT∧Q→ (Z 1∧Z 2∧Z 3) 3. PT∧Q→ ¬□(PT→Q) From ZA 3. ◇(PT∧Q) From 1 4. ◇(PT∧Q)→ □(PT→Q) M 3 _______ ¬□(PT→Q)∧□(PT→Q) ✓ ✓

The promises and pitfalls of the Constitutive Route • Its promise: – It avoids the charge of logical redundancy. It builds the zombie argument into the demonstration that PT∧Q is contradictory, so that the zombie argument is an integral part of the resulting inconceivability-entails-impossibility based refutation of materialism. • The pitfall: – It relies on this premise: 2. (PT∧Q) → (Z 1∧Z 2∧Z 3) – It is simply far from obvious how this could be proved

So, the Constitutive Route carries the following prohibitive cost: • Cost B: acknowledging that the zombie argument’s proponent has a major unmet burden—namely, that of showing why her premise that (PT∧Q) → (Z 1∧Z 2∧Z 3) should be accepted.

The Non-Constitutive Route ✓ ✓ ✗ ✓ ✓ � PT∧Q …. . Argument S _______ r∧¬r ✓ ✓

Why “Stopgap”? • The zombie arguments premises plus M 2 and M 3 tell us that M 1 is false, and thus that PT∧Q is contradictory. • But we have not yet found the contradiction yet (we haven’t found S). • So at present, we can’t use S+AIA to refute materialism. We need to rely on the zombie argument instead. • When we do find S, then S+AIA will make the zombie argument logically redundant. • Thus the zombie argument is a mere “stopgap” argument, that will eventually be superseded.

The Stopgap Route, and the Materialist’s Revenge ✗ ✓ ✓ ✓ ? PT∧Q …. . Argument S' _______ r∧¬r

• To make the Stopgap Route work Chalmers would need to somehow break the symmetry between his position and that of his materialist foe. • He would need to show that there is a stronger case for thinking that Z 1 is true than for thinking that M 1 is true.

Approach 1 • Might he simply rely on the fact that no contradiction has yet been found in PT∧¬Q in order to show that, probably, no such contradiction exists, and thus that Z 1 is probably true? • No, because the Stopgap Route requires him to admit that no contradiction has yet been found in PT∧Q either (so there is an equally good reason to think M 1 is true).

Approach 2 • Might he try to break the symmetry between Z 1 and M 1 by appealing to asymmetry of contradiction-hunting effort? • No, because the anti-materilaists would be very poor philosophers indeed if they had no searched long and hard for a contradiction in PT∧Q (since this would secure them a clinching, AIA-based refutation of materialism).

Approach 3 • Might Chalmers break the symmetry between Z 1 and M 1 by providing what we a ‘Z 1 Proof’, this being a knockdown, deductive proof that PT∧¬Q is contradiction-free and thus that Z 1 is true? • Maybe. But: (i) the burden is on him to describe such a proof; (ii) to the best of our knowledge, he has not discharged this burden (iii) In taking this approach Chalmers would be conceding victory to his opponent, to the extent of admitting that the zombie argument is inadequate in its present form because it needs to be supplemented with a major new element—in the form of a Z 1 Proof—in order to be viable.

Approach 4 • Might Chalmers try to break the symmetry between Z 1 and M 1 by arguing that we can “positively conceive” PT∧¬Q but not PT∧Q? – To ‘positively conceive’ of a situation is to model it in one’s imagination, and thereby construct a kind of (low grade) ‘existence proof’ that it is possible (and hence contradiction-free). • But the materialist won’t accept this. She thinks PT∧Q is actually true. As far as she is concerned, the act of positively conceiving PT∧Q is identical to the act of conceiving actually obtaining states of affairs. Thus the materialist positively conceives of PT∧Q all the time, so to speak, in dayto-day life. • Chalmers might contend that the materialist is mistaken in thinking she can positively conceive of PT∧Q. But to back this claim up, he would need to demonstrate that PT∧Q is contradictory, and therefore incapable of being positively imagined. But the idea that he can do this is completely at odds with the idea behind the Stopgap Route, which is that the zombie argument is not yet logically redundant because the contradiction in PT∧Q has not yet been found.

Approach 5 • Might Chalmers try to tilt the balance for Z 1 and against M 1 by appealing to the idea that it is somehow easier to imagine PT∧¬Q being true (e. g. , by imagining zombies) than to imagine PT∧Q being true (e. g. , by imagining conscious states to be identical to physical or functional brain states)? • This approach is untenable for two reasons. 1. Materialists will not accept the premise, since they find it perfectly easy to imagine PT∧Q being true. (After all, they think it is true. ) 2. It relies on the dubious principle that the ease with which we can imagine a proposition’s being true is a reliable guide to its chances of being contradiction-free.

So, the Stopgap Route carries the following prohibitive cost: • Cost C: admitting that it is the antimaterialist’s burden to provide a Z 1 Proof, and admitting that extant versions of the zombie argument, which do not incorporate such a proof, are fallacious.

The Demonstrative Route ✓ ✓ ✓ ✗ ✓ ✓ ✓ PT∧Q TUWQOPBH JDALDGYOAS Argument S _______ r∧¬r ✓ ✓

So, the Stopgap Route carries the following prohibitive cost: • Cost D: admitting that it is the antimaterialist’s burden to provide S.

The Demonstrative Route also creates the problem of logical redundancy • We are aware of only one way in which Chalmers might respond to the problem: • Buttressing Argument: If some particularly obdurate materialist is resistant to being persuaded by S+AIA, then the zombie argument will be able to serve a valuable role for the antimaterialist as a backup argument, and vice versa. – I. e. , it is better for the anti-materialist two have two arguments up her sleeve than only one.

Why the Buttressing Argument is no good 1. Under the demonstrative route, Chalmers demonstrates S in order to avoid the problems that afflict the zombie argument if he doesn’t demonstate S. But this being so, the zombie argument is unpersuasive unless S is provided. But this being so, it provides to reason to deny materialism that is logically independent of S+AIA. 2. Two arguments can provide useful support for each other only if they are of similar persuasive force. But S+AIA would provide a much stronger argument for anti-materialism than the zombie argument.

The Non-Austere Route ✗ ✗ ✓ ✓ ✗

Schomonceivability • Let ◇sp represent the claim that p is ‘schmonceivable’, where this is a ‘catch all’ name for whichever epistemically accessible property of a proposition (perhaps primary ideal positive conceivability, but we leave this open) a proponent of the zombie argument who chooses the Non-Austere Route would opt to put in place of austere conceivability.