If someone were to lend me a time machine and ask me to go back and figure out exactly what first set me down my road to dedicated descriptivism, I would first ask them if perhaps there wasn’t a better use for this marvelous contraption. But if they persisted, the coordinates I’d start with would be my elementary school days. I suspect it was some time around then that I first asked for permission to do something and was met with one of the archetypal prescriptions.
“Can I go to the bathroom?”, I surely must have asked, and just as surely a teacher must have answered, “I don’t know, can you?”
The irritation that I felt at this correction was so severe that even though I can’t remember when this happened, nor who did it to me, I still can call to mind the way it made me seethe. It was clear to me that the pedant was wrong, but I couldn’t figure out quite how to explain it. So, at the risk of sounding like I’m trying to settle a two-decade-old grudge, let’s look at whether it makes sense to correct this. I say that the answer is no — or at the very least, that one oughtn’t to correct it so snootily. […]
You can see there’s a changeover in the mid-1960s, when the usage levels ofMay Ifinish plunging andCan Istarts rocketing away. As you well know, this sort of fairly sudden change in relative frequency tends to generate a backlash against the newly-prominent form as a sign of linguistic apocalypse, so there’s no real surprise that people would loudly oppose permissiveCan I. As always, the loud opposition to it is one of the surest signs that it’s passed a point of no return. By my youth,Can Iwas ensconced as the question of choice, and nowadays, I doubt many of our kids are getting being corrected on it — though it remains prominent enough in our zeitgeist to function as a set-up fora range of uninspired jokes.
So historically, what can we say of can and may and permission and ability? We’ve seen something of a historical switch. In the distant past, may could indicate either permission or ability, while can was restricted to ability. Over time, may‘s domain has receded, and can‘s has expanded. In modern usage, can has taken on permission senses as well as its existing ability senses. May, on the other hand, has become largely restricted to the permission sense, although there are some “possibility”-type usages that still touch on ability, especially when speaking of the future:
I think there’s also another reason that correcting people on “can” versus “may” seems annoying. It’s implicature. Even if the person seems to be literally asking “Am I able to go to the bathroom?”, this would generally not make sense as a question to ask. So the Cooperative Principle (Maxim of Relevance) implies that you should interpret a person’s utterances as relevant to the conversation, which means that since the logical thing for them to be asking is whether they’re allowed, this is probably the best way to interpret the question. Replying “I don’t know, can you?” is being non-cooperative and understandably annoying.