Peter Lupu e-mails:
A comment to mull over regarding your premise (A) in your recent post about Eliminative Materialism.
A. If a proposition is true, then it is possibly such that it is believed by someone.
Premise (A) says that in order for a proposition to be true, it is a necessary condition that it can be the content of someone's belief. But there may be true propositions that cannot be for one reason or another the content of our beliefs. For instance, perhaps there are true mathematical propositions that are so complicated or so long or require such a complicated proof that it would be simply impossible for the human mind to believe. Perhaps some other mind, for instance God's mind, can comprehend them, know them, and hence believe them: but no mortal mind can do so. Thus, it seems that premise (A) requires the existence of a deity in order to make it work.
Good point. (A) is subject to scope ambiguity as between:
A*. If a proposition p is true, then there exists a subject S such that, possibly, S believes that p.
A**. If a proposition p is true, then, possibly there exists a subject S and S believes that p.
Given Peter's point above, (A*) would seem to require for its truth that there be a divine mind. But all I need for my argument against eliminative materialism is (A**), which does not require for its truth that there exist any mind, let alone a divine mind. What (A**) says is that a necessary condition of a proposition's being true as that it be possible that there exist a believer of it.
My point was that the concept of truth is the concept of something that cannot be coherently conceived except in relation to the epistemic concepts of belief and knowledge. Now there needn't be any beliefs for there to be true (or false) propositions. But if beliefs are not possible, then neither are true propositions. Now eliminative materialism implies not only that there are no beliefs, but that there cannot be any. But then there cannot be any true propositions either.
Recall the argument against beliefs. It went like this: (1) If beliefs are anything, then they are brain states; (2) beliefs exhibit original intentionality; (3) no physical state, and thus no brain state, exhibits original intentionality; therefore (4) there are no beliefs. Since each of the premises is a necessary truth if it is a truth, the conclusion, which validly follows, is a necessary truth if it is a truth.
Thus the EM-er does not merely claim that, as a matter of fact, there are no beliefs; his claim is that there cannot be any. Of course, that renders his position even more absurd. But that's not my problem!
CORRECTION (12/18): Peter rightly points out that (A**) needs tweaking. Consider its contrapositive which is logically equivalent: If it is not possible that there exist a subject S such that S believes that p, then it is not the case that p is true. Unfortunately, the consequent of the contrapositive conditional could be taken to mean that p is not true, and thus (assuming Bivalence) false, when the idea is rather that p lacks a truth-value. So (A**) ought to be replaced by
A***. If a proposition p has a truth-value, then, possibly there exists a subject S such that S believes (disbelieves, entertains, etc.) that p.
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