Few persons can claim to be entirely free from slips of speech in the use of these auxiliaries. Simply to express a future action or event, shall is used with the first person and will with the second and third; as,
I shall read, We shall read,
You will read, You will read,
He will read, They will read.
But when I desire to show determination on my part to do a certain thing, or when I exercise my authority over another, or express promise, command, or threat, will is used in the first person and shall in the second and third; as,
I will read, We will read,
You shall read, You shall read,
He shall read, They shall read.
Shall primarily implies obligation; will implies intention or purpose. Will and would should be used whenever the subject names the one whose will controls the action; shall and should must be employed whenever the one named by the subject is under the control of another.
The difference between should and would is, in general, about the same as that between shall and will.
The foregoing suggestions cover the ordinary uses of these auxiliaries, but there are some special cases deserving attention.
Will, in the first person, expresses assent or promise, as well as determination; as,
“I will read this poem for you since you have requested it.”