"If you turn left at the next corner, you will see a blue house at the end of the street." That sentence -- a conditional -- might be true even though it is possible that you will not see a blue house at the end of the street when you turn left at the next corner. A moving van may block your view; the house may have been painted pink; a crow might swoop down and peck out your eyes. Still, in some contexts, we might ignore these possibilities and correctly assert the conditional.
According to the received view of linguistic communication, the primary function of language is to enable speakers to reveal the propositional contents of their thoughts to hearers. Speakers are able to do this because they share with their hearers an understanding of the meanings of words.