Q: God only knows how many times my parents corrected me for using “can” instead of “may” to ask permission. I probably corrected my own children just as often, but I finally gave up. I assume this is a lost cause.
A: Yes, it’s a lost cause, as you learned from struggling with your children, and it was probably a lost cause when your parents were struggling with you.
The old rule is that “can” means “able to” and “may” means “permitted to.” For example, “Jesse can run fast” and “May I go for a jog, Mom?”
However, dictionaries now accept the use of both “can” and “may” as auxiliary verbs for asking permission, though some suggest that “can” here is informal.
As Merriam-Webster Unabridged explains, “The use of can to ask or grant permission has been common since the 19th century and is well established, although some commentators feel may is more appropriate in formal contexts.”
The M-W lexicographers suggest that the permission sense of “can” evolved from the use of both auxiliaries to express possibility, “because the possibility of one’s doing something may depend on another’s acquiescence.”
Although the use of “can” to indicate permission became more popular in the 19th century, the usage actually showed up hundreds of years earlier, initially as to grant permission.
The first citation in the Oxford English Dictionary is from The Book of Fayttes of Armes and of Chyualrye, William Caxton’s 1489 translation from the French of a work by Christine de Pisan:
“Þe lawe saithe suche a man can not make noo testament nor mary himself nor entre in to religyon.” (The term “can not” here means “is not permitted to.”)
The first OED citation in which “can” is used to ask for permission, rather than to grant it, is from a 1677 French-English dictionary by the Swiss-born English writer Guy Miege:
“Y a-t-il moien que je lui parle? Can I speak with him?” (Literally, Y a-t-il moyen que je lui parle? means “Is there any way I can talk to him?”)
Although “may” has been used in the sense of granting permission since Anglo-Saxon times, it wasn’t used to ask for permission until the 17th century, according to citations in the OED.
At first it was used indirectly in parenthetical expressions, as in this example from Conjectura Cabbalistica, an essay by the English philosopher Henry More on cabbalistic views of Moses:
“Justice did but, if I may so speak, play and sport together in the businesse.”
As it turns out, the earliest Oxford citation for “may” used in the direct sense you’re asking about showed up two centuries after the dictionary’s first citation for “can” used that way:
“May we take your coach to town? I saw it in the hangar” (from The History of Henry Esmond, an 1852 novel by William Makepeace Thackeray).
Thus both etymology and common usage support using “can” to ask for permission.
So where did the old rule come from? Merriam-Webster’s Dictionary of English Usage says Samuel Johnson was one of the first language authorities to draw “a strict line of demarcation” between “can” and “may.”
The “can” entry in Johnson’s 1755 dictionary says: “It is distinguished from may, as power from permission; I can do it, it is within my power; I may do it, it is allowed to me: but in poetry they are confounded.”
The M-W usage guide says Johnson’s “definition of can shows that he was ignorant of the origin of the word” and didn’t know its earliest senses, “although such uses may have been the ‘confounded’ ones he found in poetry.”