Difference between Shall and May

Key Difference: Shall is generally used to express an intended provision in the form of offers or suggestions. On the other hand, may is generally used to express possibility or permission. It is also used to denote a wish or hope. Shall is considered to be more formal than may. Shall is also comparatively more old-fashioned. However, both are used to denote propositions about the future.

‘Shall’ and ‘may’ might create some confusion as both are modal verbs. However, they both are somewhat different from each other. Shall is used to express an intended provision. It is used to denote propositions about the future. Shall is used with first person pronouns like I and we to form the future tense. For example, Shall we go to classes? It is important to be noted that shall can also be used to form other type of sentences, but it often sounds formal and old-fashioned. Shall with second and third person pronouns is used to express a strong determination. For example - You shall come by 5.30 p.m.

May is generally used to express a wish. For example - May he rest in peace. May is also used in subordinate clause so that the purpose can be depicted. For example - use good ointment so that the scar may heal. In this sentence, may is indicating a possibility. May is also generally used in context to permissions. For example - May I go out for sometime? - the person is seeking permission to go out.

According to Dictionary.com may is defined as -

(used to express possibility): It may rain.
(used to express opportunity or permission): You may enter.
(used to express contingency, especially in clauses indicating condition, concession, purpose, result, etc.): I may be wrong but I think you would be wise to go. Times may change but human nature stays the same.
(used to express wish or prayer): May you live to an old age.
Archaic. (used to express ability or power.)

According to Dictionary.com shall is defined as -

plan to, intend to, or expect to: I shall go later.
will have to, is determined to, or definitely will: You shall do it. He shall do it.
(in laws, directives, etc.) must; is or are obliged to: The meetings of the council shall be public.
(used interrogatively in questions, often in invitations): Shall we go?

Comparison between Shall and May:

	Shall	May
Definition	Shall is used to express an intended provision. It is used to denote propositions about the future	On the other hand, may is used to express possibility or permission. It is also used to denote a wish or hope.
Origin	Old English sceal, Northumbrian scule "I owe/he owes, will have to, ought to, must"	Old English mæg "am able" (infinitive magan, past tense meahte, mihte)
Main Concept	Offers/suggestions with ''I' and 'we'	Possibility Permission
Example	Shall we go to party? I shall retire to my room.	He may get the medal. May I go to visit Aunt Mary?
Type	Modal Verb	Modal Verb