The basic assumption that there is a common store of thoughts surely can be denied; in fact, it had been plausibly denied a century ealier by critics of the theory of ideas who argued that it is a mistake to interpret the expression "John has a thought" (desire, intention, etc.) on the analogy of "John has a diamond." In the former case... the expression means only "John thinks" (desires, etc.), and provides no grounds for positing "thoughts" to which John stands in a relation. To say that people have similar thoughts is to say that they think alike, perhaps so much alike that we even say they have the same thought, as we say that two people live in the same place. But from this we cannot move to saying that there are thoughts that they share, or a store of such thoughts. Philosophers have been misled by the 'surface grammar' of a 'systematically misleading expression.'... Argument is required to show that thoughts are entities that are 'possessed,' as diamonds are. How solid the argument is may be questioned, in my opinion.
hold the phone, noam! i mean, i agree that there isn't a mind full of thoughts the way there's a mine full of diamonds. but the use of the phrase "john has a thought" doesn't imply that at all, and it certainly doesn't mean exactly the same thing as 'john thinks'.
our ability to say 'john has a thought' indicates only our potential ability to imagine thoughts as objects capable of being possessed. to argue about the actual existence of those thoughts, or even the assertion that 'thoughts' exist based on the sentence is to miss the point.
semantics assumes that each element in a sentence should have similar contributions to the meaning. meaning that in 'john has a thought', and 'john has a diamond,' diamonds and thoughts should contribute the same type of meaning to the sentence - in this case, they are objects that john can posses. and i love semantics, but this is why it has to change. 'john has a' does NOT mean the same thing in each of these sentences.
the sentence isn't a puzzle with pieces missing. what goes in the object position changes the entire sentence, changes the meaning of the verb, changes the meaning of the subject, changes the context, the reason for speaking, and so on.
no one has ever seen a thought; they don't exist in the physical world. but they're important to talk about. and the concept is built up from our talking about it. our ability to conceive of them as objects, or even of 'think' as a verb is a matter of convenience. the use of 'thought' in the language shouldn't be mistaken for an assumption that it exists, but only as a useful way of categorizing a phenomenon that we NEED to discuss.