In a previous post I argued against Eliezer Yudkowsky, Robin Hanson, and others, that Philosophical zombies are conceivable. In this one I challenge the P-zombie argument against physicalism.

P-zombies are usually invoked to argue that physicalism is false. Philosophers seem to agree that this is the case:

It seems that if zombies really are possible, then physicalism is false and some kind of dualism is true. For many philosophers that is the chief importance of the zombie idea. [...]

However, not everyone agrees that physicalism entails the impossibility of zombies. One suggestion is that physicalists can concede there are possible worlds which are exact duplicates of our world in all purely physical respects, but where the physical properties which give rise to consciousness in our world are prevented from doing so: there are items in those worlds which block consciousness. In that case physicalists can consistently allow the possibility of zombie worlds (Leuenberger 2008. On such ‘blockers’ see Hawthorne 2002b; Chalmers 2010, 163-165). This approach, however, is obviously inconsistent with maintaining that conscious states are either identical with or constituted by physical or functional states. So it is not clear that physicalists can consistently allow the possibility of consciousness-blockers.(SEP)

Here, the argument:

  1. Conceivably, there is a physical duplicate (i.e. something physically identical in every way) of you that lacks qualia.
  2. Conceivability implies possibility.
  3. Therefore, possibly, there is a physical duplicate of you that lacks qualia.
  4. Therefore, your qualia are not physical states. (Because identity is necessary; if your qualia are identical to (proper subparts of) your brain, then it's impossible to have the brain without the qualia.)
  5. Therefore, there is a mind that's not completely physical.
  6. Therefore, token-physicalism is false.

Physicalism, note, is usually considered by physicalists to be a contingent truth, not a necessary one. That is, there can be non-physicalist worlds, according to physicalists. It just so happens that it is true in our universe, in the same way that planets exist, but not in the same way that 1+1=2.

Some philosophers (e.g. Davidson 1970) have thought of physicalism as a conceptual or necessary truth, if it is true at all. But most have thought of it as contingent, a truth about our world which might have been otherwise. (SEP)

If physicalism were a necessary truth, then P-zombies would be incompatible with it, and so physicalism would be refuted by the thought experiment. But it is not a necessary truth, so P-zombies pose no problem to it. The P-zombies argument just shows that there can be universes where physicalism is false.

An example: It is possible to hold these four propositions as true at the same time:

  1. In our universe, physicalism is true. Consciousness is an epiphenomenon. Certain physical systems give rise to it, but it doesn't do anything.
  2. In another universe, physicalism is true. Consciousness is a real causal entity that affects, and is affected by, the environment. (This seems to be Eliezer Yudkowsky's position here)
  3. In other universes, physicalism is false. Dualism is true.
  4. In other universes, physicalism is true. Consciousness does not exist, and beings are P-zombies in that universe.

That is, consciousness could work differently in different universes. That is, unless someone has a convincing argument for one model of consciousness as a necessary truth.

Universes 1 and 2 are externally similar, and only if you knew the relevant physical laws in each of the you could see which one has P-zombies and which one has regular humans.

There could be, though, one way to tell them apart: imagine that we discover how consciousness works in our universe, and which precise systems are conscious are which aren't based on external characteristics of them. Then, there would be a set of physical laws (And perhaps fundamental consciousness particles or something like that) that explains how consciousness works. If we then go to Universe 2, those laws wouldn't be there, and so you would know that that is a P-zombie universe.

A reply could be that Universe 2 has the same physical laws and fundamental entities than Universe 1, and still lack consciousness. But that begs the question against physicalism. I claim that it is not possible to conceive of beings like us in an universe like ours, with whatever laws govern consciousness, but that are unconscious. If those laws are there, they will be conscious.

If I am right in what I outlined here, I find myself against the consensus of philosophers without having done a full literature review, so my conclusion is tentative. I state my argument once more:

  1. Physicalism is not metaphysically necessary (Consensus of philosophers)
  2. Various models of consciousness are metaphysically possible (Consensus of philosophers?)
  3. P-zombies are conceivable (From previous post)
  4. P-zombies are possible (From 3)
  5. There are possible universes where physicalism is true/false and P-zombies exist/do not exist (From 1,2,4)
  6. Hence, the truth of physicalism and of the P-zombie thesis are independent (Any combination is possible)  (From 5, Definition of independence)
  7. Hence, accepting one conclusion regarding one of them does not entail anything about the other.
  8. Hence, accepting the possibility of P-zombies does not refute physicalism.