Tractatus Logico-Philosophicus by Ludwig Wittgenstein + comments  by Maarten Maartensz   

3.4 A proposition determines a place in logical space. The existence of this logical place is guaranteed by the mere existence of the constituents - by the existence of the proposition with a sense.

This "logical space" is a mere manner of speaking, but not a bad one, for it has at least the merit of making the point that a proposition means something only in some supposed domain, world, situation, universe of discourse - or indeed logical space. This must be somehow presupposed or given, and one important point about it is that generally there is more in it than the mere meaning of the proposition one considers.

The rest of W.'s claim may be restated as: A proposition has a meaning only if there is supposed to be some domain of things and combinations of things or facts and some rule such that the proposition represents a (possible) fact in the domain.

However, here again lies a subtle confusion hidden that also played a role later and with others:

Such a domain or universe of discourse is arbitrary and is supplied when interpreting the proposition. It is arbitrary in that one may take a proposition to be about the real world, or an imagined world, say that of Homeros or a play of Shakespeare, and that the same proposition may mean different things in different supposed domains.

Finally, the confusion I mean is that very often - usually - the propositions people do use are far clearer to them and others as regards to what they mean than as regards to whether what they mean is in fact so in whatever domain someone may presuppose or suppose: Meaning and truth do not coincide, and what one understands are meanings rather than truths, even if what is meant is known to be true. (And incidentally: For ordinary men, what people believe is what they mean that coincides with or seems supported by their wishful thinking, but this is an aside on the multitudes one should follow neither in evil, nor in nonsense, nor in superstitions.)