Since what is referred to is a simple, no general idea qualifies. There is no genuine referring to any universal, even logical ones. Necessity cannot be a subject, the only way in which necessity shows itself is in logical tautology. For example, the disjunction of all possible states of affairs is necessary, but this says nothing about necessity within the world. Similarly, impossibility shows itself in self-contradictions, which can say nothing.
Possibility is ubiquitous among the sayable, and therefore contrasts with nothing.
These classical modalities make no reference. Non-simple subject terms are analyzed into descriptions which have only simple subjects with transcendent reference. The notion that the sayable is exhausted by a cosmological tautology constructed of all fully analyzed sentences, then so are all discursive truths, since they are contained in the sayable. The problem of truth, then, is the problem of confirmation of a sentence-truth match. The upshot, then, is what we deeply wish to say we cannot say, but we can say the contingent propositions of the natural sciences, carving out a piece of the cosmological tautology.