Online research in philosophy

Back in the late 1950s, a wonderful thing happened to metaphysics.

The inference from conceivability to possibility has been challenged in numerous ways. One of these ways is the so-called phenomenal concept strategy, which has become one of the main strategies against the conceivability argument against physicalism. However, David Chalmers has recently presented a dilemma for the phenomenal concept strategy, and he has argued that no version of the strategy can succeed. In this paper, I examine the dilemma, and I argue that there is a way out of it. I conclude that Chalmers has not posed any serious problem for the phenomenal concept strategy to succeed in blocking the conceivability argument. In doing so, my aim is not only to show that Chalmers’s argument has not refuted the phenomenal concept strategy, but also to clarify what any version of the strategy should achieve in order to be successful.

The inference from conceivability to possibility has been challenged in numerous ways. One of these ways is the so-called phenomenal concept strategy, which has become one of the main strategies against the conceivability argument against physicalism. However, David Chalmers has recently presented a dilemma for the phenomenal concept strategy, and he has argued that no version of the strategy can succeed. In this paper, I examine the dilemma, and I argue that there is a way out of it. I conclude that Chalmers has not posed any serious problem for the phenomenal concept strategy to succeed in blocking the conceivability argument. In doing so, my aim is not only to show that Chalmers’s argument has not refuted the phenomenal concept strategy, but also to clarify what any version of the strategy should achieve in order to be successful.

A number of popular arguments for dualism start from a premise about an epistemic gap between physical truths about truths about consciousness, and infer an ontological gap between physical processes and consciousness. Arguments of this sort include the conceivability argument, the knowledge argument, the explanatory-gap argument, and the property dualism argument. Such arguments are often resisted on the grounds that epistemic premises do not entail ontological conclusion. My view is that one can legitimately infer ontological conclusions from epistemic premises, if one is very careful about how one reasons. To do so, the best way is to reason first from epistemic premises to modal conclusions (about necessity and possibility), and from there to ontological conclusions. Here, the crucial issue is the link between the epistemic and modal domains. How can one reason from theses about what is knowable or conceivable to theses about what is necessary or possible? To bridge the epistemic and modal domains, the framework of two-dimensional semantics can play a central role. I have used this framework in earlier work (Chalmers 1996) to mount an argument against materialism. Here, I want to revisit the argument, laying it out in a more explicit and careful form, and responding to a number of objections. In what follows I will concentrate mostly on the conceivability argument. I think that very similar considerations apply to the other arguments mentioned above, however. In the final section of the paper, I show how this analysis might yield a unified treatment of a number of anti-materialist arguments.

David Chalmers supports his contention that there is a possible world populated by our zombie twins by arguing for the assumption that conceivability entails possibility. But, I argue, the modal epistemology he sets forth, ‘modal rationalism,’ ignores the problem of incompleteness and relies on an idealized notion of conceivability. As a consequence, this epistemology can’t justify our quotidian judgments of possibility, let alone those judgments that concern the mind/body connection. Working from the analogy that the imagination is to the possible as perception is to the actual, I set forth a competing epistemology, ‘modal empiricism.’ This epistemology survives the incompleteness objection and allows some of our everyday modal judgments to be justified. But this epistemology can’t justify the claim that Zombie World is possible, which leaves Chalmers’s property dualism without the support it needs.

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.

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.

Chalmers argues that zombies are possible and that therefore consciousness does not supervene on physical facts, which shows the falsity of materialism. The crucial step in this argument – that zombies are possible – follows from their conceivability and hence depends on assuming that conceivability implies possibility. But while Chalmers’s defense of this assumption – call it the conceivability principle – is the key part of his argument, it has not been well understood. As I see it, Chalmers’s defense of the conceivability principle comes in his response to the so-called objection from a posteriori necessity. The defense aims at showing that there is no gap between conceivability and possibility since no such gap can be generated by necessary a posteriori truths. I will argue that while Chalmers is right to the extent that there is no gap between conceivability and possibility within the standard Kripkean model of a posteriori necessity, his general conclusion is not justified. This is because the conceivability principle might be inconsistent with a posteriori necessity understood in some non-Kripkean way and Chalmers has not shown that no such alternative understanding of a posteriori necessity is available.