A Priori Neuroscience

Either Ned Block's Blockhead counts as thinking, or it's an empirical matter what possible configurations of stuff would count as thinking. For, suppose the claim labeled (2), below, were true and knowable a priori. Then you could do a priori neuroscience as follows:
(1)I think (Descartes).
(2)A blockhead (i.e. a big physical system which passes the turing test just by having a big look-up table, with all possible series of questions that could be asked in, say, half an hour) would not count as thinking. (Ned Block)**
(3)Therefore, some part of me (call it my brain) is not a big look-up table.


**in the paper where he introduces the blockhead, Block argues that such a machine would not count as 'intelligent', not that it wouldn't count as 'thinking' but I presume he would also accept a similar claim for 'thinking'?


Now, the blockhead is explicitly cooked up to be a worse-case scenario for what physical stuff might realize a given behavior, so if you admit that the blockhead thinks it's hard to see how you could deny that any other thing with suitable behavior would count as thinking. Thus, rejecting a posteriori necessities, seems to be a direct route to behaviorism!

I wonder if this could have motivated Wittgenstein's near behaviorism? I don't remember if he ever retracts the serious use of a prior=necessary in the Tractatus...and there definitely is that passage about 'what if you opened your skull and there was nothing inside?', so he does seem to have thought about these issues...
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