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I'm trying to understand David Chalmers' two-dimensional argument against materialism in philosophy of mind (here). I'm particularly confused by the paragraph (pp. 11-12) where he claims that it's not necessary for the primary and secondary intensions of Q to coincide in order for the argument to go through (in his framework, Q is any phenomenal truth about our world). Could anyone clarify? What would a formal presentation of the argument be, assuming that the two intensions of Q are different?

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    – Geoffrey Thomas
    Commented Apr 20 at 9:42
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    SEP summarizes Chalmers's argument, including workarounds when P or Q are semantically unstable (primary and secondary intensions differ), see notes 25 and 26. They are more comprehensible than Chalmers's own remarks. He replaces the phenomenal property in Q (say pain) with its epistemic 1-intension (say pain') and then reruns the argument with that. It gives him a metaphysically possible world physically identical to ours but without pain'. Therefore, pain' does not supervene on the physical and physicalism fails.
    – Conifold
    Commented Apr 20 at 10:56
  • Thank you for the reply. If I understand correctly, the lion's share here is done by the modal rationalist thesis that for every epistemically possible scenario there is a metaphysically possible world. But still, isn't that conflating 1-possibility with 2-possibility? Why can't the materialist counteract that, absent the semantic stability of Q, (P & NOT Q) is 1-possible but not 2-possible (like 'water is not H2O')? Commented Apr 20 at 17:20
  • You are correct, and denying modal rationalism (P4 in SEP) is a popular response. Chalmers counters that opponents cannot produce convincing counterexamples to the thesis in other domains, so the denial seems ad hoc. Another popular response is to deny apriori coherence (P2). That we can "ideally" track coherence of our premises in complex matters is directly contradicted by non-trivial theorems and open problems in mathematics. Hintikka called it the "scandal of deduction", see What is the difference between depth and surface information?
    – Conifold
    Commented Apr 22 at 1:18
  • @Conifold Why are Kripkean a posteriori necessities not a counterexample to modal rationalism? To me, they just seem the paradigmatic case of something which is 1-possible but not 2-possible (i.e., something for which there is an epistemically possible scenario but not a metaphysically possible world). What am I missing? Commented Apr 22 at 18:04

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Chalmers' argument is difficult to follow, with all his modal conceptual transforms. It is similar to a math proof in which one has multiple variable transforms, but much harder to follow as he is using English words not math designations.

I have not worried about parsing Chalmers' argument, as I think it is actually irrelevant. He is attempting a logic disproof of the claim that our world is necessarily materialistic. This is the whole point of "conceivability" arguments. I think this logic argument is correct, our world is NOT necessarily materialistic. But necessity is not what most materialists are claiming, hence the disproof's irrelevance. The best way to understand materialism is that it is an empirical claim about what ontological model best fits our world, not a claim that other models are impossible in principle, and Chalmers argument is irrelevant against this understanding of materialism. Under this understanding, it is trivially true that we all could have been zombies, but there is good empirical evidence that we are not.

There are some materialists who claim that this world is "metaphysically necessary", and causative, in his comments end up defending this claim. His rejection of modal reasoning is therefore misplaced, as metaphysical possibility and necessity is what modal reasoning is all about. Chalmers repeatedly references Kripke, and his modal necessitarian thinking. Kripke is still considered, by analytic philosophers, to be a savior of analyticity through his modal formulations. A Kripkean refutation of causative's claim is explicitly what Chalmers is doing, and causitive's refusal to delve into the reasoning in it, is a disappointing response. Chalmers argument, which I have not traced in detail, is that it is both logically and metaphysically possible for our world to be epiphenomenally dualist, hence zombies are both logiclaly and metaphysiclaly possible, and the necessitarian claim that consciousness is necessarily a property of material humanity, is untrue. This argument will have a valid way to be constructed, whether Chalmers succeeded or not.

Aside on Kripke -- here is an answer in which I articulate why analytic philosophers celebrate Kripke, and why empiricists such as myself reject his thinking: https://philosophy.stackexchange.com/a/93974/29339

Chalmers in his paper often does a bait/switch between materialism and physicalism. This is understandable, as physicalists do this themselves. The problem for analytic philosophers who do this, is that physicalism is not a clearly definable claim, and analyticity needs clear and explicit definitions to operate on. Materialism is clearly definable -- it is the claim that there is only one ontological substrate to our universe, and that is matter. The switch to "physicalism" occurred in philosophy when physics empirically refuted materialism with the modern physics breakthroughs of the turn of the 20th century, which showed that mater is not actually fundamental. Physicalism replaces "materialism" with the alternate claim that there is one fundamental ontology to our universe, and we don't yet know what it is, but it is what physics studies. This leaves physicalism without an ontology, only a methodology.

Chalmers does not delve into this problem, which is most clearly articulated in Hempel's Dilemma -- one cannot specify a definition of physicalism that excludes consciousness, spirits, and Gods as potential aspects of "physics" that is not clearly false. And as the most central precept most physicalists hold by is that consciousness and spirits cannot be causal, which leads to a contradiction vs. the intrinsic openness of the scientific method. Additional problems are traceable to the inability of science to justify its own method, and the centrality of abstractions and relationships in actual science, such that physics is at least ontologically dualist (matter plus abstractions).

Chalmers ignores these further complexities, challenges, and ambiguities for physicalism, and treats his modal refutation of materialism as applicable to physicalism too.

As an empiricist, I consider the empirical refutations of materialism, and the further empirical and logic problems for the switch to physicalism, to be far more important attacks on materialism/physicalism. But for those who hold by analyticity instead, then Chalmers arguments are relevant.

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