H. P. Grice on "will-b"/ "will-d" and "shall-b"/"shall-d"

The distinction between shall and will as future markers arose from the practice of Latin teaching in English schools in the 14th century. 

It was customary to use will to translate the Latin velle (meaning to wish, want or intend); this left shall (which had no other equivalent in Latin) to translate the Latin future tense.