Definition of: shall

(shal)
A defective verb having a past tense should, an archaic present second person singular, (thou) shalt, past (thou) shouldst or shouldest, and no other inflected forms. It is now used only as an auxiliary followed by the infinitive without to, or elliptically with the infinitive unexpressed. Its function is to indicate, now chiefly in formal discourse:
1. In the first person, simple futurity, with a matter–of–fact attitude toward the action or state projected: We shall take only the usual precautions. (But see usage note below.)
2. In the second and third persons, futurity combined with a mood or feeling of: a Determination: They shall not pass. b Promise: You shall have whatever you need. c. Threat: You shall pay for this. d Command: No one shall twice be put in jeopardy. e Inevitability: When earthly time shall end, will life survive?
3. In all persons, indefinite future time in conditional statements: If and when you or we or the divers shall locate the treasure, it will (or, in legal use, the mandatory shall) be shared out according to the agreement.
4. In all persons, futurity involving ideal certainty, in clauses following expressions of anxiety, demand, or desire: They are anxious, indeed insist, that you or I or both of us shall go, rather than any outsider. [OE sceal I am obliged, 1st person sing. of sceolan] ♦ shall vs. will
The traditional view on the use of shall and will is that to indicate simple futurity shall is used in the first person, will in the second and third; their roles are reversed to express determination, promise, threat, command, inevitability, etc.; while in questions, the choice between them depends on which one is expected in the answer. These statements hold fairly well for legal usage, but they are too arbitrary to describe accurately the facts of current American usage in speech and writing, except at the most stilted formal level. Shall and will have had a tendency gradually to exchange roles once each century since 1500, and during the present century it has been the turn of will to make its way into the lead. In the important task of indicating simple future time in the first person, will has largely replaced shall, aided in doing so by the leveling effect of the contraction 'll: I'll (= I will or I shall) be free at ten. Shall, thus displaced, takes on one role assigned by traditional formula to will, and is used in the first person to express determination plus inevitability, as in General MacArthur's “I shall return” and Winston Churchill's “.. . and win we shall.” If will in the first person is to express determination according to the formula, it must be stressed or qualified in some way: I will too go out and play. In questions in the first person, shall is still commonly used to express the simple future, but it is also found as the hortatory shall, either humorously formal: Shall we (= Let's) dance? or politely threatening: Shall we (= Let's) do it my way for once. Again, will has won out over shall when it comes to giving routine or polite, as distinct from peremptory, commands: You will proceed to Hill 90 and occupy it. The peremptory shall in the second person is now usually replaced, except in legal usage, by will with have to: You will have to (= shall) go whether you want to or not. It is hazardous to try to sum up the present position of these two forms, but with the few exceptions noted, in American usage will now usually indicates the simple future in all persons, while shall expresses the future complicated by some feeling about it.