Humans are the only species with true language. Monkeys can respond differently to different calls, and chimps can learn a few symbols. But to have true language, you have to have vivid imagination, which is unique to humans.
Language can communicate situations that do not yet exist—the future tense. In English, we could say if he will go. In French, s’il ira. But even more than this, language can communicate an alternate reality that is different from the one you are experiencing. If he were to go implies that he is not going to go. In French, s’il aille. This is the subjunctive, as it were. You can even have a past subjunctive: if he had gone, s’il soit allé. Language students hate learning subjunctives, but they are a marvel of intellect. That does not mean, of course, that you have to like them.