|shall | will|
In his 1653 book Grammatica Linguae Anglicanae, John Wallis promoted the following rules:
(1) When using the first person, the simple future should be expressed with shall
(e.g. I shall dine with the prescriptivists ).
(2) When using the second and third person, the simple future should be expressed with will
(e.g. He will get drunk with the descriptivists ).
Note: Prior to 1653, this distinction was not made. Since then it has been observed, but with great difficulty because the rules are both artificial and unnatural.
1. Many people use shall to express offers and suggestions.
Shall we dance?
2. Some legal codes use shall, shall not, and shalt not to express mandatory behavior.
Thou shalt not kill. (Exodus 20:13)
Quotation - "In Old and Middle English times, shall and will were sometimes used to express simple futurity, though as a rule they implied, respectively, obligation [shall] and volition [will].
The present prescribed use of these words … stems ultimately from the seventeenth century, the rules having first been codified by John Wallis, an eminent professor of geometry at Oxford who wrote in Latin a grammar of the English language. ….
Despite a crusade of more than three centuries on behalf of the distinction, the rule for making it is still largely a mystery for most Americans, who get along very well in expressing futurity and willfulness without it."
(Source: The Origins and Development of the English Language, Thomas Pyles)