Grammar Girl here.

Today's topic is “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! Guest-writer Bonnie Trenga, writes,

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.”

“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?”

“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. That’s why one authority states that “educated people” typically say, “Can’t I?” instead of “Mayn’t I?” or “May I not?” (1). 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?” Microsoft Word doesn’t even recognize “mayn’t” as a word. So “mayn’t” will probably be obsolete soon, if it isn’t already.

Which One?

Now we can ponder Donna’s question about “Can or may we expect you tomorrow?” We need to ask ourselves if the speaker is talking about ability or permission. I don’t think it’s 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?” No.

I’ve ruminated on it for a while and I have a feeling that the word “might” would be better: “Might we expect you tomorrow?” Although this sentence is somewhat formal, I’m uncertain of the context. This opens up a whole avenue of discussion. Luckily, we’ve already covered the difference between “may” and “might.” Just go to http://grammar.quickanddirtytips.com/may-might.aspx to hear all about it.

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

Summary

You may now discuss this conundrum among yourselves. You have my permission. Don’t worry, though, if you can’t figure it out. I don’t have the ability either. In short, it’s OK to use “can” instead of “may” if you’re speaking informally, but if you’re being formal or polite, use “may” when you’re speaking about authorization.

Administrative

This podcast was written by Bonnie Trenga, author of The Curious Case of the Misplaced Modifier, who blogs at sentencesleuth.blogspot.com, and I'm Mignon Fogarty, the author of the paperback book Grammar Girl's Quick and Dirty Tips for Better Writing.

Finally, I have a couple of things to thank you for! First, thank you for voting Grammar Girl the best education podcast of 2008 in the Podcast Awards. I'm truly honored. Second, thank you for writing all your pet peeves in the comments section two weeks ago. I'm going through them and thinking about the best way to choose a winner.

That's all. Thanks for listening.

References

1. Garner, B. Garner's Modern English Usage. Oxford: Oxford University Press. 2003, p. 124.

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.