Daniel Stoljar has a new paper, "Two Conceivability Arguments Compared", forthcoming in PAS
. There, he compares these two arguments:
The Zombie Argument:
Z1. Zombies (physical duplicates of us, with different phenomenal properties) are conceivable
Z2. If zombies are conceivable, zombies are possible
Z3. Ergo, zombies are possible
The Actor Argument:
A1. Actors (behavioural duplicates of us, with different phenomenal properties) are conceivable
A2. If actors are conceivable, actors are possible
A3. Ergo, actors are possible
The Zombie Argument (ZA) is used to defeat physicalism. The Actor Arguments (AA) is used to defeat behaviourism, or so Stoljar claims. He argues that reflection on the similarities among these arguments can pose problems for the phenomenal concept strategy.
Stoljar assumes that AA is a good argument against behaviourism. He points out that AA is usually presented to undergraduate students as a sound refutation of behaviourism. He also assumes that AA and ZA are of the same kind, that is, they are both concerned with the inference from conceivability to possibility, and the relation between phenomenal and (some or all) physical truths.
Using these two assumptions, Stoljar argues that the phenomenal concept strategy is committed to rejecting AA. The PC strategy claims that Z1 does not entail Z3, because Z1 has an alternative explanation which does not entail Z3. Stoljar argues that if AA and ZA are of the same kind, then the PC strategy would have to say that A1 has an alternative explanation which does not entail A3, so that AA would not be sound. But AA is sound, he assumes. So the PC strategy is incorrect.
I am working on a response to this argument. My thought is that we can disambiguate AA in two ways:
A1*: Actors are conceivable
A2*: If S is conceivable, S is possible
A3*: If actors are conceivable, then actors are possible
A4*: Ergo, actors are possible
A1': Actors are conceivable
A2': If actors are conceivable, actors are possible
A3': Ergo, actors are possible
I think that Stoljar's argument equivocates on these two readings of the actor argument. For there is no single reading of it that makes both of his assumptions plausible:
Assumption 1 (AA and CA are of the same kind) is plausible only under reading AA*. That is, advocates of ZA take it that the conceivability of zombies entails the possibility of zombies because conceivability entails possibility
Assumption 2 (AA is sound) is plausible only under reading AA'. AA' will be sound if the argument is valid and all the premises are true. Under reading AA' it is uncontroversial that AA' is sound, since it is uncontroversial that A1' and A3' are true. And since A2' is just a material conditional, if the consequent is true, the conditional is true. So it is uncontroversial that AA' is sound. But it is not uncontroversial that AA* is sound: premise A2* is precisely what is at issue in these debates.
Could Stoljar understand ZA in a similar way to AA', so that both assumptions involve the actor argument in the sense of AA'? Let's see:
Z1*: Zombies are conceivable
Z2*: If S is conceivable, S is possible
Z3*: If zombies are conceivable, zombies are possible
Z4*: Ergo, zombies are possible
Z1': Zombies are conceivable
Z2': If zombies are conceivable, zombies are possible
Z3': Ergo, zombies are possible
If we consider ZA' and AA', then we can safely assume that the zombie argument and the actor argument are of the same kind, and we can also assume that the actor argument is sound. Does this pose a problem for the PC strategy?
Well, not really. Because the PC strategy is not committed to saying that AA' is unsound, even if they do claim that ZA' is unsound. The strategy entails that conceivability of zombies is not a reliable guide to the possibility of zombies. It also entails that the conceivability of actors is not a reliable guide to the possibility of actors. But, of course, this is compatible with the claim that actors are both conceivable and possible.
Putting the point in a different way: when we compare ZA* and AA*, if
we assume that AA* is sound, then the PC strategy is in trouble because their response against ZA* entails that AA* is unsound too: they will deny Z2* and A2* (which are the same). But, of course, it is very controversial to claim that AA* is sound. In my paper, I plan to argue that Putnam and Block's arguments against behaviourism are not of the form AA*.