g—there’s no possible world that’s physically identical to ours but where the Boeing’s don’t fly. There is a possible world that’s physically identical to ours that lacks consciousness. That’s the difference. It shows that physics suffices for flight but not fully-fledged mentality. (N.B. the interesting case here is not minds without brains, but brains without minds.)
Nick Hay—Thanks for bringing this back to the key issue. In fact I do not “consider having successfully determined a conclusion from pure thought evidence that that thought is correct”. I take my evidence to be something beyond myself: whatever premises guided my reasoning, not the mere psychological fact of my concluding as I did. (This is why I brought up the content/vehicle distinction in my original comment.) Granted, reasoning presupposes that one’s thought processes are reliable, and a subjectively convincing line of thought may be undermined by showing that the thinker was rationally incapacitated at the time (due to a deceptive drug, say). But presuppositions are not premises.
Compare:
(1) P, therefore Q
(2) If I were to think about it, I would conclude that Q. Therefore Q.
These are different arguments! If I come to believe Q via #2, my evidence is the (hypothetical) brain process you talk about. But in the first case, my evidence is simply P, and not any fact about me at all.
P.S. Nobody denies that a priori justifiable claims may also be justified empirically, say by the testimony of a reliable thinker, or by observing a reliable brain or other computational engine. But it’s a different kind of justification. And of course the mere fact that there is a second argument for a conclusion does nothing to show that the first one was flawed.
g—there’s no possible world that’s physically identical to ours but where the Boeing’s don’t fly. There is a possible world that’s physically identical to ours that lacks consciousness. That’s the difference. It shows that physics suffices for flight but not fully-fledged mentality. (N.B. the interesting case here is not minds without brains, but brains without minds.)
Nick Hay—Thanks for bringing this back to the key issue. In fact I do not “consider having successfully determined a conclusion from pure thought evidence that that thought is correct”. I take my evidence to be something beyond myself: whatever premises guided my reasoning, not the mere psychological fact of my concluding as I did. (This is why I brought up the content/vehicle distinction in my original comment.) Granted, reasoning presupposes that one’s thought processes are reliable, and a subjectively convincing line of thought may be undermined by showing that the thinker was rationally incapacitated at the time (due to a deceptive drug, say). But presuppositions are not premises.
Compare: (1) P, therefore Q (2) If I were to think about it, I would conclude that Q. Therefore Q.
These are different arguments! If I come to believe Q via #2, my evidence is the (hypothetical) brain process you talk about. But in the first case, my evidence is simply P, and not any fact about me at all.
P.S. Nobody denies that a priori justifiable claims may also be justified empirically, say by the testimony of a reliable thinker, or by observing a reliable brain or other computational engine. But it’s a different kind of justification. And of course the mere fact that there is a second argument for a conclusion does nothing to show that the first one was flawed.