Do not believe what they say about shall and will, that the difference between them is unimportant and not worth the trouble to understand. You will hear this from some teachers and read it in some manuals, but there is a meaningful distinction to be made between these two verbs, tricky though it might be at first to discern. Let’s see what we can learn about it here in the space of a page.
First, let’s acknowledge that contemporary English does in fact no longer care to distinguish carefully between these two verbs, preferring will to shall in almost all regular circumstances of both writing and speech. If anywhere shall is preserved, it is in legal documents, but even there respected authorities of modern English usage argue that it might well be time to let shall go its way. However that may be, there is more of English than only its contemporary productions, and we will be cheating ourselves of the richness of conceptions that our own literature of the past meant to distinguish if we don’t at least begin to comprehend the difference between these two old verbs. One cares about shall and will, that is to say, not to try to bring the usage back, but to understand its subtlety when we ourselves wish to go back.
When, for example, Shakespeare has his Juliet ask her Romeo, “What o’clock tomorrow shall I send to thee?” and he answers, “By the hour of nine,” Juliet replies in turn, “I will not fail,” adding painfully what all of us have known in such a moment: “’tis twenty year till then.” But why “shall I” in one sentence and “I will” a moment later? We would not have expected her to say, “What o’clock will I send,” but perhaps the gentler “should I send” would have been in order. The latter choice of should would take us too far afield to discuss here, but we can ask for a brief explanation of how shall and will differ between Juliet’s question and her vow.
Shall and will were once both principal verbs in English, shall meaning to be under an obligation imposed and will meaning to intend or promise or wish. The two verbs are used most often now, however, as auxiliary verbs along with an infinitive to build the future tense. That means, then, that English in its more traditional form recognizes that the future can come about in two different ways: something will happen either as the result of an obligation or determination imposed, or as the result of things simply unfolding as regularly they will. Any person accused of a crime shall have the right to a trial, because the law imposes that requirement; but the sun will rise again tomorrow because it is in the very nature of the physical setup that such will occur.
Now if that were all there is to it, we could resign ourselves to understanding the distinction without undue effort. But for reasons too involved to detail here, the two verbs mix and match their forms among the three grammatical persons. Thus, the obligatory, or imposed, future is denoted by I will, you shall, he, she, it shall (to present only the singular), and the simple, or inevitable, future is denoted by I shall, you will, he, she, it will (again presenting only the singular to keep things manageable). And when one is posing a question about the future, as Juliet does to Romeo, the form that is used is the form expected in reply.
So when Juliet asks at what hour shall I, she is expecting Romeo to reply (and he does so elliptically) you shall, putting her thereby under an obligation we can only assume she welcomes. For her to have asked at what hour will I would have been to ask him to read, not make, the future. And contrariwise, when she replies to Romeo’s answer, she asserts I will not fail, intending with the verb will in the first person to indicate her own resolve and determination to bring that particular future about.
Yes, this grammatical differentiation of futures is involved and subtle, but so too are human motivations to either accept or determine the future. Again, this is no argument to restore to English its once careful indications of subsequent time, but it is to suggest that we can miss the deeper and more intricate implications of our best literature when we don’t familiarize ourselves, however superficially, with what the language could once do regularly. And anything that can shed more light on our intellectual life, as an old phrase had it, can only be to our good.
***