What's the evidence for 2)?

Every human being is conscious.

Every human being is conscious. — quine

Apart from the ones that happen to be asleep.

Every human being is conscious. — quine

And what's the evidence for this?

It's like infinite regress of evidence.

It's like infinite regress of evidence — quine

Not necessarily. Presumably there's some sort of falsifiable evidence that hasn't yet been falsified which acts as a fundamental premise?

So, what's your objection to my argument?

So, what's your objection to my argument? — quine

That the second premise isn't supported.

What makes you think so?

(1) If P-zombies exist, then there is a thing that is human and non-conscious. — quine

I would take issue with this one. A physically identical being lacking consciousness is not human. It's a p-zombie.

But then we're arguing semantics and not whether p-zombies are possible.

Leaving aside all the problems tom alluded to with premise two, like sleeping persons and persons in comas:

We need to establish what exactly you mean by "human". I will assume you are referring to persons (in this case, human beings with thoughts of their own), not just the biological bodies of a human based on premise two. I can reject premise one, as under that definition, p-zombies are not human. They are simply animated human bodies that perfectly replicate the physical aspects of a person, right down to their brain waves, but do not possess consciousness.

If you want to argue human in terms of biological body, then premise two is false, as p-zombies would be human and not possess consciousness.

Also, to point out, p-zombies do not need to actually exist; they only need to be logically conceivable.

Many things are logically conceivable. Merely logically conceivable things can't refute anything. P-zombies are logically conceivable. Do P-zombies refute physicalism? I don't think so.

Then you do not understand the original p-zombie argument.

Logically conceivability entails logical possibility. Logical possibility means that there exists a possible world in which p-zombies exist. Therefore, there exists a possible world in which everything is physically the same, except that some of the "humans" are p-zombies i.e. physically identical, but not conscious. Therefore, what we call consciousness cannot be reduced to the physical, and therefore, there exists something beyond the physical, meaning physicalism is false.

Let's put an example to it:

There is our world. Let's call it World 1, or W1 for short. In this world, Chany is a person who has a physical body, brain waves and all that, and is conscious. There is another logically possible world, World 2, or W2 for short, that is exactly the same as W1 except that instead of Chany, there is p-zombie in place of Chany. Again, p-zombies are logically conceivable, meaning that they are logically possible; there is nothing wrong with W2 potentially existing. Let's call this p-zombie zombie-Chany. Chany and zombie-Chany are physically identical: same body, same brain states, everything. The only difference is that Chany has consciousness and zombie-Chany does not. Whatever explains this difference, it cannot be physical, as Chany and zombie-Chany are physically identical. Therefore, we need to appeal to something beyond physicalism to explain consciousness: therefore, physicallism is false.

That the second premise isn't supported. — Michael

So you're saying that the semantic content of statements in an argument matter? You were ignoring that idea with the p-zombie argument and only focusing on its form as a modus ponens.

What makes you think so? — quine

The fact that you've just asserted it and haven't provided any evidence to support it.

Logically conceivability entails logical possibility. — Chany

This seems dubious to me unless we're simply saying that conceivability is logical possibility.

And with respect to logical possibility, what domain are we referring to for our background? That is, what set of statements forms our base, or are we referring to metaphysical/ontological facts, or what?

I ask because obviously if our background domain includes "physicalism is true" for example, then p-zombies aren't logically possible in that domain.

I ask because obviously if our background domain includes "physicalism is true" for example, then p-zombies aren't logically possible in that domain. — Terrapin Station

Is this by definition?

Logical possibility means that there exists a possible world in which p-zombies exist. — Chany

If a world exists it is an actual world, not a possible world (although of course insofar as a world is actual it must be also possible). Something being logically possible does not entail that it is anywhere actual.

Is this by definition? — Marchesk

The idea is that something is logically possible just when it isn't contradictory. Well, whether it's contradictory is relative to the domain we're considering. That could be metaphysical facts, or some set of statements, or whatever. If we're assessing whether "p-zombies are conceivable" is logically possible relatve to some set of statements, then it wouldn't be logically possible relative to a set of statements that includes "physicalism is true."

then it wouldn't be logically possible relative to a set of statements that includes "physicalism is true." — Terrapin Station

Sure, but "physicalism is true" is what's in question, so that would be assuming the conclusion.

Sure, but "physicalism is true" is what's in question, so that would be assuming the conclusion. — Marchesk

Hence why I'm asking what we're saying it's logically possible with respect to.

Hence why I'm asking what we're saying it's logically possible with respect to. — Terrapin Station

If we're trying to determine whether physicalism is true, we can ask whether it's logically possible for there to be a duplicate physical world lacking some X from our world.

Of course, if you already know that physicalism is true, then you don't need to ask such questions. But then, how do you know that physicalism is the case?

we can ask whether it's logically possible for there to be a duplicate physical world lacking some X from our world. — Marchesk

Oy--this is just what I'm talking about though. Logically possible with respect to what? Metaphysical facts? Some set of statements? Logical possibility is relative to some domain. We're not simply asking whether "p-zombies are possible" isn't contradictory to itself, are we? That wouldn't tell us much.

We're not simply asking whether "p-zombies are possible" isn't contradictory to itself, are we? That wouldn't tell us much. — Terrapin Station

We're asking whether physicalism logically entails all Xs. If it doesn't, then some Xs aren't physical.

We're asking whether physicalism can logically account for all Xs. — Marchesk

What does it mean to "logically account" for something empirical? Sounds fancy, but I think it doesn't actually mean anything.

What does it mean to "logically account" for something empirical? Sounds fancy, but I think it doesn't actually mean anything. — Terrapin Station

Physicalism isn't empirical. It's a metaphysical doctrine.

Physicalism isn't empirical. It's a metaphysical doctrine. — Marchesk

The bulk of metaphysics is ontology, no? And it's sounding more and more like you're simply giving up on trying to support the logical possibility/"logically account for" angle.

The bulk of metaphysics is ontology, no? — Terrapin Station

Ontology and empiricism are two different concerns.

Anyway, I meant to edit my post to add:

As such, it needs to show how everything is exclusively physical or made up of the physical.

Consider Thales: everything is water. So the challenge for water metaphysicians is to show how something like fire is made up of water.

You can substitute consciousness for fire, and physics for water. Colin McGinn titled his book on consciousness, "The Mysterious Flame", so it's apropos.

Ontology and empiricism are two different concerns. — Marchesk

So ontology doesn't deal with empirical things in your view? Time isn't empirical for example? "Everything is water" isn't an empirical claim?

So ontology doesn't deal with empirical things in your view? Time isn't empirical for example? "Everything is water" isn't an empirical claim? — Terrapin Station

Empiricism is a matter of how we know, not what exists. So no, time isn't empirical, except in that we know about time by experiencing it. "Everything is water" is most certainly not an empirical claim, although empirical investigation can help or hurt such claims.