Eliezer—It’s just fundamentally mistaken to conflate reasoning with “observing your own brain as evidence”. For one thing, no amount of mere observation will suffice to bring us to a conclusion, as Lewis Carroll’s tortoise taught us. Further, it mistakes content and vehicle. When I judge that p, and subsequently infer q, the basis for my inference is simply p—the proposition itself—and not the psychological fact that I judge that p. I could infer some things from the latter fact too, of course, but that’s a very different matter. (And in turn distinct from inferring things from the second-order judgment that I judge that p!)
Anyway, here’s a simple argument for the inescapability of a priori justification:
For any instance of empirical justification, it seems like we can construct a parallel instance of a priori justification simply through conditionalization. Suppose that empirical evidence E would justify your drawing conclusion C. Then presumably you could justifiably believe the conditional “if E then C” prior to experiencing E. We can repeat this procedure to conditionalize out all empirical grounds for belief, and the result will be a conditional statement that is justifiable a priori—i.e. not dependent on any particular experiences or empirical evidence at all.
Tom McCabe wrote: “If you argued that an airplane was not really “identical” to the pile of parts, but that they just “always went together”, people would look at you like you had three heads. Yet, when applied to brains, people think this argument makes sense.”
This is because there is nothing more to our concept of being an airplane than the reduction basis. Any possible world with all the parts arranged in the right way is immediately recognizable, under that description, as a world containing an airplane. Indeed, that’s just what it is to be an airplane. Minds are a rather different matter. They are not conceptually reducible to neurons firing. It is conceptually possible for the two to come apart (if we imagine a world with different laws of nature, perhaps), so they are not simply one and the same thing.
(Philosophers have written books on this argument, so I don’t pretend that the above is incontrovertible. But it is certainly not so easily dismissed as Tom and others—including my past self—might assume. More detail here.)
Eliezer—It’s just fundamentally mistaken to conflate reasoning with “observing your own brain as evidence”. For one thing, no amount of mere observation will suffice to bring us to a conclusion, as Lewis Carroll’s tortoise taught us. Further, it mistakes content and vehicle. When I judge that p, and subsequently infer q, the basis for my inference is simply p—the proposition itself—and not the psychological fact that I judge that p. I could infer some things from the latter fact too, of course, but that’s a very different matter. (And in turn distinct from inferring things from the second-order judgment that I judge that p!)
Anyway, here’s a simple argument for the inescapability of a priori justification:
For any instance of empirical justification, it seems like we can construct a parallel instance of a priori justification simply through conditionalization. Suppose that empirical evidence E would justify your drawing conclusion C. Then presumably you could justifiably believe the conditional “if E then C” prior to experiencing E. We can repeat this procedure to conditionalize out all empirical grounds for belief, and the result will be a conditional statement that is justifiable a priori—i.e. not dependent on any particular experiences or empirical evidence at all.
Tom McCabe wrote: “If you argued that an airplane was not really “identical” to the pile of parts, but that they just “always went together”, people would look at you like you had three heads. Yet, when applied to brains, people think this argument makes sense.”
This is because there is nothing more to our concept of being an airplane than the reduction basis. Any possible world with all the parts arranged in the right way is immediately recognizable, under that description, as a world containing an airplane. Indeed, that’s just what it is to be an airplane. Minds are a rather different matter. They are not conceptually reducible to neurons firing. It is conceptually possible for the two to come apart (if we imagine a world with different laws of nature, perhaps), so they are not simply one and the same thing.
(Philosophers have written books on this argument, so I don’t pretend that the above is incontrovertible. But it is certainly not so easily dismissed as Tom and others—including my past self—might assume. More detail here.)