Online research in philosophy

Zombies, as conceived by philosophers these days, are supposed to be creatures that are physically indistinguishable from normal people that nevertheless completely lack phenomenal consciousness. The kind of zombie I want to focus on is one that is molecule- by-molecule identical to a healthy, normal, adult human being living in a world physically like ours — indeed this might be our own actual world. To make things more concrete, pick any such person that you actually know. Let this be John. John is not a zombie. Now consider an exact, perfect, physical replica of John, call him Zhon. Note that because John and Zhon are physically alike, they are also behaviorally and functionally alike. So if you were to encounter Zhon, you could not distinguish him from John. Under the imagined circumstances so far, you would normally expect Zhon to be conscious as well. But let’s stipulate that Zhon has no conscious experiences whatsoever — he’s never had them, nor will he ever have them. So Zhon, according to this stipulation, doesn’t know — indeed cannot know — what it is like to have conscious experiences of any kind. There is nothing it is like to be Zhon. Zhon lacks conscious phenomenology altogether. If Zhon were to be a metaphysically possible creature, he would be a zombie.1 So this is the notion of zombie I would like to focus on. According to many philosophers, Zhon is a possible creature, and that is because Zhon is a conceivable creature. This gives us the argument from zombies against physicalism. Physicalism is the doctrine that says: all that exist is physical through and through, including conscious minds and their conscious experiences. The zombie argument, as we might call it, is a species of conceivability arguments: 1. If Zhon is conceivable, then Zhon is possible. 2. Zhon is conceivable. 3. Hence, Zhon is possible. Now since the choice of Zhon was arbitrary, we can, of course, generalize the argument to all zombies like Zhon — that is, to zombies that are physically indistinguishable, in relevant respects, to healthy, normal, adult human beings..

In recent years the 'zombie argument' has come to occupy a central role in the case against physicalist views of consciousness, in large part because of the powerful advocacy it has received from David Chalmers.1 In this paper I seek to neutralize it by showing that a parallel argument can be run for physicalism, an argument turning on the conceivability of what I shall call anti-zombies. I shall argue that the result is a stand-off, and that the zombie argument offers no independent reason to reject physicalism.

This paper examines the ramifications of Hume's view of the relation of conceivability to metaphysical possibility. It argues that the limitations Hume places of the representations involved in moves to conceivability to metaphysical possibility preclude any straightforward argument against full-blooded causal realism in Hume from conceivability. Furthermore, our finding certain states of affairs conceivable when they are not metaphysically possible is perfectly compatible with the thrust of the causal realist position.

David Chalmers' conceivability argument against physicalism relies on the entailment from a priori conceivability to metaphysical possibility. The a posteriori physicalist rejects this premise, but is consequently committed to psychophysical strong necessities. These don't fit into the Kripkean model of the necessary a posteriori, and they are therefore, according to Chalmers, problematic. But given semantic assumptions that are essential to the conceivability argument, there is reason to believe in microphysical strong necessities. This means that some of Chalmers' criticism is unwarranted, and the rest equally afflicts the dualist. Moreover, given that these assumptions are independently plausible, there's a general case to be made for the existence of strong necessities outside the psychophysical domain.

Brian Loar believes he has refuted all those antiphysicalist arguments that take as their point of departure observations about what is or isn't conceivable. I argue that there remains an important, popular and plausible-looking form of conceivability argument that Loar has entirely overlooked. Though he may not have realized it, Saul Kripke presents, or comes close to presenting, two fundamentally different forms of conceivability argument. I distinguish the two arguments and point out that while Loar has succeeded in refuting one of Kripke's arguments he has not refuted the other. Loar is mistaken: physicalism still faces an apparently insurmountable conceptual obstacle.

This paper was chosen by The Philosopher’s Annual as one of the ten best articles appearing in print in 2000. Reprinted in Volume XXIII of The Philosopher’s Annual. In his very influential book David Chalmers argues that if physicalism is true then every positive truth is a priori entailed by the full physical description – this is called “the a priori entailment thesis – but ascriptions of phenomenal consciousness are not so entailed and he concludes that Physicalism is false. As he puts it, “zombies” are metaphysically possible. I attempt to show (I think successfully) that this argument is refuted by considering an analogous argument in the mouth of a zombie. The conclusion of this argument is false so one of the premises is false. I argue at length that this shows that the original conceivability argument also has a false premise and so is invalid.

The phenomenal concept strategy is one of the most attractive responses to the so-called conceivability arguments. A crucial step in these arguments is the inference from conceivability to possibility. The phenomenal concept strategy attacks this inference from conceivability to possibility: they argue that there is an alternative explanation of the conceivability of zombies, which does not involve the possibility of zombies. This alternative explanation appeals to special features of phenomenal concepts in order to explain the conceivability of zombies. Daniel Stoljar has recently argued that if the phenomenal concept strategy was a good strategy against the conceivability argument against physicalism, it would also be a good strategy against the conceivability argument against behaviourism. But he claims that the latter conceivability argument is sound, and therefore the phenomenal concept strategy cannot be correct. In this paper I show how the phenomenal concept strategy can respond to this objection.

The conclusion of this argument (hereafter ZA) entails the falsity of physicalism because, technical details aside, physicalism is or entails the thesis that every psychological truth is entailed by some physical truth. If it is possible that I have a zombie duplicate however, then it is possible that the physical truths are as they are and some psychological truth is different. Hence 3 entails that physicalism is false. The second conceivability argument is one that is almost as famous, though perhaps it is less famous for being a conceivability argument: the perfect actor argument against behaviorism (see, e.g., Putnam 1963, 1975). In a version that is both familiar and relatively clear, it goes like this.

According to the zombie conceivability argument, phenomenal zombies are conceivable, and hence possible, and hence physicalism is false. Critics of the conceivability argument have responded by denying either that zombies are conceivable or that they are possible. Much of the controversy hinges on how to establish and understand what is conceivable, what is possible, and the link between the two—matters that are at least as obscure and controversial as whether consciousness is physical. Because of this, the debate over physicalism is unlikely to be resolved by thinking about zombies—or at least, zombies as discussed by philosophers to date.



In this paper, I explore an alternative strategy against the zombie conceivability argument. I accept the possibility of zombies and ask whether that possibility is accessible (in the sense of ‘accessible’ used in possible world semantics) to our world. It turns out that the question of whether zombie worlds are accessible to our world is equivalent to the question of whether physicalism is true. By assuming that zombie worlds are accessible to our world, supporters of the zombie conceivability argument beg the question against physicalists. I will then consider what happens if a supporter of the zombie conceivability argument should insist that zombie worlds are accessible to our world. I will argue that the same ingredients used in the zombie conceivability argument—whatever they might be—can be used to construct an argument to the opposite conclusion. If that is correct, we reach a stalemate between physicalism and property dualism: while the possibility of some zombies entails property dualism, the possibility of other creatures entails physicalism. Since these two possibilities are inconsistent, one of them is not genuine. To resolve this stalemate, we need more than thought experiments.