Modal verbs of Permission: May, Can, & Could

Modal verbs are auxiliary verbs that express necessity, possibility, permission, or ability.

Among these, the verbs "may," "can," and "could" are frequently used to ask for or give permission, with each of these modals having its nuances and levels of formality or politeness.

May

"May" is considered the most formal and polite way to ask for permission. It is typically used in official requests, formal settings, or when speaking to someone you don't know very well.

So using "may" shows respect and courtesy. Here are some examples.

May I leave the room for a moment?
May I use your phone to make a call?
May I sit here, please?
May I borrow your book for a day?
May I speak to Mr. Smith?

Can

"Can" is used in informal contexts and is the most common way to ask for or give permission. It is straightforward but slightly less polite compared to "may."

Can I go to the restroom?
Can I take one of these cupcakes?
You can ask me something if you like.
Can I try this on?
You can open the window.

Could

"Could" is again a polite modal verb - it is more polite than "can" but less formal than "may." It can't though be used to give permission, just to ask for it.

it's used when you want to be considerate and show that you are not imposing too much.

Could I possibly borrow your charger for a moment?
Could I get your help with this?
Could I see that menu again, please?
Could I ask you a favor?
Could I join you on your walk?

Comparing Politeness and Formality

So summing up, here’s how they typically rank in terms of politeness and formality:

May: Formal and very polite. Used in professional or formal settings and when you need to show great respect.
Could: Polite but less formal than "may." Used when asking for something while implying flexibility or non-imposition.
Can: Informal and straightforward. Used in everyday situations.

When choosing which modal verb to use for permission, the speaker has to consider their relationship with the speaker, the setting, and how polite or formal they want to be.