My question may seem strange and nonsensical for some, therefore I will try to explain myself to the best of my ability. So to make it clearer what I mean with my question. I will start by quoting the very beginning of Propositions from SEP (Stanford Encyclopedia of Philosophy):
The term ‘proposition’ has a broad use in contemporary philosophy. It is used to refer to some or all of the following: the primary bearers of truth-value, the objects of belief and other “propositional attitudes” (i.e., what is believed, doubted, etc.1), the referents of that-clauses, and the meanings of sentences.
I am mainly concerned with: the primary bearers of truth-value. So that is how I will define what I mean with propositions. Therefore, semantic answers like the following, or something similar:
A proposition is not a proposition until it has been proposed.
is not the answer I am looking for because that would not answer my question. For example, you can think that something is a proposition, but in fact is not a proposition. Namely, the proposition fails to be truth-apt. Because, it does not meet my definition: the primary bearers of truth-value. We are now getting closer to the essence of my question. I think claims about the ontological is either true or false, so whenever we have a concept of something it is either a proposition or it is not a proposition. The question is; if we do not have a concept about x, would it still be a proposition? Because even if we do not have a concept of x - the ontological fact of said unknown x is still either existent or nonexistent.