Several days ago we revisited a long list of rules from the 1930s about the use of "shall" and "will" that are basically no longer observed in our language.
Some GTOTD subscribers asked what the current rules are.
In current editions of Harbrace, there are hardly any mentions of "shall" and "will" at all. In section 7c (2) on the subjunctive mood, there is a small note that reads, "The indicative is displacing the use of the subjunctive, just as will is displacing shall -- except in questions such as "Shall we go?"
If we go back to the first edition of Harbrace, from 1941, Professor Hodges followed up his section on the subjunctive (then 7e) with the following page-long section on Shall and Will:
7f. Use the correct form for shall (should) and will (would).
Informal English is rapidly dropping the distinctions between shall and will, should and would. Except for the use of should to express an obligation (see below), the tendency is to use everywhere will and would.
But careful usage still observes the following rules:
(1) To express the simple future tense use shall (should) in the first person and will (would) in the second and third.
RIGHT . . . I shall stay. He will go. You will find me at home. We shall expect you.
(2) To express determination (or in making a promise) use will (would) in the first person and shall (should) in the second and third.
RIGHT . . . I will help. You shall have your reward. He shall not obstruct our passage.
(3) In questions, use the form expected in the answer.
RIGHT . . . Shall you remain longer in the country? [Answer expected: I shall, or I shall not.]
RIGHT . . . Will you go in spite of all the dangers? [Answer expected: I will; I am determined to go.]
(4) Use should in all persons to express an obligation.
RIGHT . . . I (you, he, we they) should help the needy.
(5) Use would in all persons to express customary or habitual action.
RIGHT . . . I (you, he, we they) would take a vacation at the end of the summer.