In more than twelve years of writing this column, we have somehow escaped dealing with the difference between “can” and “may.” That aversion ends because of a friend’s request:
“Please, please write about how many people are misusing ‘can’ when they mean ‘may.’ It’s making my head hurt. I just saw the headline ‘President Trump can’t use $3.6 billion in military funds for border wall construction, federal court rules,’ and it’s wrong! He has the ability to spend the money, but he doesn’t have permission to do so!”
Yes, the friend is a grammar stickler. Let’s hope they remain a friend after this column.
The confusion, if there is one, comes from traditional usage. “Can” has meant the ability to do something: “Now that her homework is finished, she can go to the park to play.” Compare that to “Now that her homework is finished, she may go to the park to play.”
Don’t see a difference? Many people would agree with you. But to those with finely attuned grammatical senses, the sentence with “may” might be less clear. Does that mean she has permission to go to the park? Or that she has the choice of going to the park or perhaps going to the store instead?
“Can” is an auxiliary verb, also known as a helping verb, meaning its use in a phrase gives greater context to another verb by specifying tense, voice, emphasis, and so on. Descended from Germanic languages, it meant “to know, to understand, to know how, (as auxiliary) to be able to, to have ability or opportunity,” the Oxford English Dictionary says.
“May” has a similar etymological history, is slightly older, and originally meant “To be strong; to have power or influence,” the OED says, but quickly took on the meaning “To be able to do or be.” Both, not surprisingly, also came to mean “to have permission.” After all, who is to say whether “able” means physically able to do something or given leave to do so?
By the end of the nineteenth century, “can” and “may” became interchangeable. And when two words mean virtually the same thing, somebody typically comes along to try to make them different again.
As Merriam-Webster’s Words at Play blog notes: “It didn’t take too long for teachers and grammarians of the day to proscribe that can should only be used of ability and may of permission. . . . There is no particular reason for the rule, except for the fact that may has been used longer to mean ‘to give permission’ than can has. Nonetheless, the ‘rule’ lives on.”
The “rule” is still being taught, often without regard to the nuance needed to clearly understand our second sentence. Bryan A. Garner’s Modern English Usage says, “Although only an insufferable precisian would insist on observing the distinction in informal speech or writing (especially in questions such as ‘Can I wait until August?’), it’s often advisable to distinguish between these words.” Even so, he puts the substitution of “may” for “can” at Stage 4 of the Language-Change Index, the etiquette equivalent of “elbows on table.”
In other words, “can” and “may” can both be used when it’s a question of possibility or permission rather than ability, making our friend’s objection to the headline moot (and possibly endangering the friendship). As M-W says: “You may use can if you wish, and you can use may if it makes you feel better.” For ability, “can” rules.
“May” is the more formal of the two, often more polite. “Can I have this dance?” sounds more abrupt than “May I have this dance?” though Garner’s warns that “a fussy insistence” on using “may” “can give the writing a prissy tone.”
In the classic example used to teach many people the difference (and in this classic clip from Dirty Rotten Scoundrels), asking “Can I go to the bathroom?” or “May I go to the bathroom?” could result in a far different outcome.