The future can be a strange state of affairs, if it is really anything at all. Every time we get there, we call it the present, and then that present doesn’t last long without more future. Like the past, the future is tied to the present, and from where we are now in our minds, we can even think about what will be past in the future.
Strange, indeed, and some suspect that the whole tangled web is the work of language. Writers know that language creates a world of its own, and good writers writing for the sake of fact and clarity watch their verbs closely, so that their written world conforms to the one we actually experience together. The leading characteristic, or property, of verbs is tense (there are five properties of a verb: person, number, tense, voice, and mood), and the tense, or time, of a verb pitches the pole around which the fabric of a particular world of words, called a clause, unfolds. Because we humans seem to have this peculiar way of projecting ourselves into a world that doesn’t really yet exist, manipulating verb tenses can be tricky. But every trick, of course, has its solution.
English has two future tenses (setting aside the question of shall and will, which requires some real magic to solve): the simple future and the future perfect. The simple future means just what it says: here is what is going to happen at some time subsequent to the one we’re in right now. If I say that I will speak with him this afternoon, you know that such an event is yet to transpire. The verb phrase will speak is composed of the principal verb speak (a principal verb is the one that carries the actual idea we want to communicate), along with the auxiliary verb will (an auxiliary verb aids a principal verb in building the tense, and it always precedes its principal verb). The simple future conveys the sense that something yet to happen will at some moment in fact be happening.
But what if the future is not so simple? If I say instead that I will have spoken with him by 4:00 this afternoon, I am still referring to a future time, 4:00 this afternoon, but the act of speaking with him is to occur at some time before that late afternoon hour. That is to say, I am projecting a time (4:00 this afternoon) which is future in relation to the present moment at which I’m writing or speaking the sentence, and that future moment is to mark the boundary before which something else is yet to occur, namely, speaking with him. The future itself, in other words, contains something that will be past, and that is exactly what the future perfect tense is meant to denote. The term perfect in grammar means finished or completed, and although at first sight the name of the future perfect tense might appear to be a contradiction in terms—how can something yet to occur also be completed?—we can see from our example that such a mysterious conception is in fact possible for our mind and its language.
Time, then, can be relative, and that is of quite practical importance in writing clear sentences. It may be true as some wise philosophers aver that the truth is ultimately simple, but the path that language takes to the truth is often winding and spiral. The kind of language most of us write most of the time, what is called expository prose, tries to represent the world we live and act in, a world which, as far as our minds are concerned, is made up of both space and time. Clause by clause and sentence by sentence, we write world-like scenes for our readers to enter and live in for a moment. The more accurately we construct those linguistic worlds, the more easily our readers can see what we see and know what we know—all to the point of understanding one another all the better.