Thank you Mister Micawber. As far as I'm concerned it refers to a intelligent use of modal verbs to ask something in a polite way or offer something or permission etc.
May I / Might I / Could I borrow your pen?— Polite in any circumstances Can I borrow your pen?— Familiar; polite only with friends and family. Would you / Could you / Might you lend me your pen?— Polite in any circumstances. Will you / Can you lend me your pen?— Familiar; polite only with friends and famil