g—No, by ‘conceptually possible’ I mean ideally conceptually possible, i.e. a priori coherent, or free of internal contradiction. (Feel free to substitute ‘logical possibility’ if you are more familiar with that term.) Contingent failures of imagination on our part don’t count. So it’s open to you to argue that zombies aren’t conceptually possible after all, i.e. that further reflection would reveal a hidden contradiction in the concept. But there seems little reason, besides a dogmatic prior commitment to materialism, to think such a thing. Most (but admittedly not all) materialist philosophers grant the logical possibility of zombies, and instead dispute the inference to metaphysical possibility. This seems no less ad hoc. Anyway:
“I would like to know… why you think conceptual possibility has anything to do with actual possibility.”
I actually wrote a whole thesis on this very question, so rather than further clogging the comments here, allow me to simply provide the link. If you’re interested enough to read all that, and still have any objections to my view afterwards, I’d be very interested to hear them—my comments are open. For this page, though, I think I should bow out, unless Eliezer sees fit to address the concerns I raised about the original topic, and especially his treatment of the a priori.
Constant—Sure, there’s something to be said for epistemic externalism. But I thought Eliezer had higher ambitions than merely distinguishing rationality and reliability? He seems to be attacking the very notion of the a priori, claiming that philosophers lazily treat it as a semantic stopsign or ‘truce’ (a curious claim, since many philosophers take themselves to be more or less exclusively concerned with the a priori domain, and yet have been known to disagree with one other on occasion), and dismissively joking “it makes you wonder why a thirsty hunter-gatherer can’t use the “a priori truth factory” to locate drinkable water.” (The answer isn’t that hard to see if one honestly wonders about it for a moment or two.) But maybe you’re right, and these cheap shots are just part of the local attire, not intended for cognitive consumption.
g—I already answered this. Change the extra-physical laws of nature as you will, it is not conceptually possible for a world physically identical to ours to lack flying airplanes. What else are we to call the boeing-arranged atoms at 10000ft? The zombie (physically identical but non-conscious) world, by contrast, does seem conceptually possible. So there’s no analogy here.
TGGP—Yes, I think that, thanks to the bridging laws, “the materially-sufficient is psycho-sufficient”. This dualism is empirically indistinguishable from materialism. Anticipating experience may be a useful constraint for science, but that is not all there is to know. (See also my responses to James above.)