Suppose the theory of bare particularism is wrong. It is plausible that if it's wrong, it's not that its central claims are false, but rather its central claims are nonsense. It is not so much that "There are bare particulars" is false, as that it fails to express anything. Maybe you're not convinced by this particular example, but if so there are probably some others that you'll find convincing. I suspect that many theories in ontology are such that either they're true or they're nonsense, and they aren't all true. Platonism and trope theory are like that, for instance. I'll use bare particularism as my stand-in for such a case.
Yet we have no hesitation in saying things like:
- Sally believes that she is partly constituted by a bare particular,
We could set this orthodoxy aside, and instead of parsing "x believes that s" as predicating a relation of belief between x and the proposition that s, we could take "x believes that" to be a sentential operator. This leads to problems with quantification ("Sally believes some of the things she was just told"), but perhaps those can be solved in some way. But even if we set the orthodoxy aside, we have another problem with (1). We have a sentence that contains a component, outside of quotation marks, that is nonsense, viz., the phrase "bare particular".
The simplest solution to the problem is just to take (1) to be elliptical for some metalinguistic claim like
- Sally believes that the sentence "Sally is partly constituted by a bare particular" is true.
- It is not the case that Sally believes that she is partly constituted by a bare particular.
Another problem with reading (1) as (2) is that it is odd to attribute to Sally beliefs about bits of language. What if Sally thinks, for some good or bad reason, that there are no sentences? Again, maybe there is a reference magnet solution.
A hint of a different solution is provided by this post. That post suggests that there is something more fundamental in the mind than beliefs. There are "doxins", which place constraints on what beliefs are to be attributed to one. It may well be that when Sally accepts bare particularism, she isn't believing any proposition like "that she is constituted by a bare particular", but rather she has the doxin expressible by "The credence of the proposition expressed by 'I am constituted by a bare particular' shall be high." If in fact there were such a proposition, this doxin would allow her to be credited with belief in it. There not being any such proposition, we can't credit her with belief. Rather, we credit her with a doxin that carries a false presupposition, viz., that there is a proposition expressed by "I am constituted by a bare particular". The false presupposition, however, isn't a belief. So she can have that doxin while yet not believing in sentences and the like. There would need to be a lot of work done to defend this.
The issue comes up not just for belief. For instance, one might have a desire that "involves a bare particular". Then one would bring in orektins, from the same post.