What is the correct sentence when asking for something like while flying asking for a glass of water :

May I have a glass of water


Can I have a glass of water


1 Answer 1


The Cambridge Dictionary website ("English Grammar Today") ranges three possible modal constructions in this order of increasing politeness.

Can I ask you a question? (Informal)

Could I use your phone? (More formal/polite)

May I use your phone? (Even more formal/polite

The Oxford Dictionary also says that "Can I" is possible, although less formal:

But the 'permission' use of can is not in fact incorrect in standard English. The only difference between the two verbs is that one is more polite than the other. In informal contexts it’s perfectly acceptable to use can; in formal situations it would be better to use may.

So, if you aim for the most polite construction, you might say

May I have a glass of water, please?

It never hurts to add "please" to make the request more polite.


  • 2
    Contra Cambridge, can is not more informal than could. The latter expresses deference, but that is not the same thing as formality. There are situations, including semi-formal ones, where I would choose can over could because directness is preferred and could would be at least borderline inappropriate. Jul 2, 2016 at 14:08
  • @AlanCarmack - that's interesting, Alan. As a non-native speaker not immersed into an English-speaking community, I have to rely on "official" sources like Cambride etc. Maybe you could (or can?) post an additional answer with explanations. Jul 2, 2016 at 15:31
  • 3
    I agreed with Alan at first (and upvoted his comment), but after thinking some more, here's what I think. Could I is softer than Can I, hence more deferential and more polite, which is not the same as more formal, but that makes it more appropriate in a situation where you and the other person don't know each other—the kind of situation where you resort to greater formality. Saying Can I in that situation is an invitation to be less formal. The more formal the situation, the more that Can I means "Am I able to" rather than "Will you permit me to". …
    – Ben Kovitz
    Jul 2, 2016 at 16:34
  • 3
    … For example, if you say "Can I get a glass of water?" to a waitress, that can be heard as suggesting that the staff is unable to do their jobs, especially if you say it after you've been waiting a long time for service. "Could I get a glass of water?" doesn't invite that interpretation. (Intonation can change everything, of course, but that's another topic.) On the other hand, if you are asking about rules, Can I is formal and clear and Could I is hazy or informal; e.g. "Can I enter the building after 5:00?" But that's not a request. So, I'd say your answer is fine as-is.
    – Ben Kovitz
    Jul 2, 2016 at 16:43

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