'Can' Versus 'May'

A listener named Donna says that after familiarizing herself with the definitions and usages of “can” and “may,” she still isn't sure which word to use in this sentence: “May we expect you tomorrow?” or “Can we expect you tomorrow?”

That's a tough one! 

Ability or Permission?

Once upon a time in the land of strict grammar rules, “can” denoted physical or mental ability, and “may” denoted permission or authorization (1). It wasn't OK to use “can” if you were talking about permission. You could hear citizens of this land saying, “May I accompany you to the ball, Miss Fuzzywink?” and “Why of course you may, my dear.” This young lady perhaps would ask her suitor about his dancing ability: “Can you do the cha-cha?” and he would answer that he did have the ability: “Why of course I can, Miss Fuzzywink.”

'Can' Instead of Traditional 'May'

Nowadays, the rules aren’t so cut and dried. Since the second half of the 19th century, “can” has been used in informal contexts to denote permission (2). You’ve probably heard someone ask, “Can I go to the party?” If we lived in strict-grammar land, the authorities would complain about this usage, but these days it is acceptable to use “can” in this manner if you’re speaking informally (3). If you’re a teacher of young children, you probably often hear “Can I go to the bathroom?” Parents probably hear their children whining, “Can I have a cell phone?” So are the kids to blame for using “can” instead of “may”? Well, they just repeat what grown-ups say, and grown-ups are apparently moving away from the sometimes prissy-sounding “may.”

For example, according to the American Heritage Dictionary, the experts on its usage panel were more accepting of using “can” to mean “may” in a recent survey than they were in the past.

'May' Is OK

Now, “may” does have its rare place. If formality and politeness are of utmost importance, you should use “may” to denote permission. So it would be better to say to the waiter at a fancy restaurant, “May I have more water, please?” than “Can I have more water, please?” If you’ve just knocked on a door, you should probably say, “May I come in?”

Next: "Mayn't" and the Final Word on "Can" Versus "May"

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'Mayn’t' Isn’t OK

Before we answer Donna’s question, let’s talk about denying permission: No, you may not turn off your listening device just yet. It’s possible to say the obscure contraction “mayn’t,” but I wouldn’t recommend it. The American Heritage Dictionary says mayn’t sounds unnatural, and Garner’s Modern English Usage states that “educated people” typically say, “Can’t I?” instead of “Mayn’t I?” or “May I not?” So if we were in the land of strict grammar rules, we might hear Miss Fuzzywink asking her governess, “But why can’t I go to the ball?” Even she probably wouldn’t say, “Why mayn’t I?”

'Can' Versus 'May'

Now we can ponder Donna’s question about “Can or may we expect you tomorrow?” First, we might ask ourselves if the speaker is talking about ability or permission. I don’t think we're talking about permission: “Are we allowed to expect you tomorrow?” No.

Neither does it seem to be talking about ability—“Are we mentally able to expect you tomorrow?”—at least, not in this literal sense. But it does work in the sense of "Will we be able to expect you tomorrow?" In other words, can we make plans to have you at our house?

"Can" also has meanings beyond simple ability. For example, it can also mean to have the possibility of something, such as "I hear you can win at poker." Therefore, "Can we expect you tomorrow?" could also have the sense of "Is there a possibility that you will arrive tomorrow?"

If we want to ask, “Are you coming tomorrow?” maybe we should just say it that way. But if I were forced to choose between “can” and “may,” I would say, “Can we expect you tomorrow?”

Bonnie Mills is the author of The Curious Case of the Misplaced Modifier and blogs at sentencesleuth.blogspot.com.

References

1. Garner, B. Garner's Modern English Usage. Oxford: Oxford University Press. 2016, p. 139-40.

2. Burchfield, R. W, ed. The New Fowler’s Modern English Usage. Third edition. New York: Oxford, 1996, p. 126.

3. American Heritage Guide to Contemporary Usage and Style. Boston: Houghton Mifflin Company, 2005, p. 74.