May I correct you?

It is a common teacher's joke to respond to a student who asks, “Can I go to the bathroom?” by correcting them and saying they should ask, “May I go to the bathroom?”. Teachers seem to view the joke as both humorous and important but neither the student’s brain nor his bladder appreciates the distinction. The correction from "Can I go to the bathroom?" to "May I go to the bathroom?" is based on a prescriptive rule that distinguishes ability from permission. In actual English usage, however, "can" is commonly used to ask for permission, and native speakers understand it that way. From a descriptive linguistic perspective, "Can I go to the bathroom?" is correct because it follows established usage and communicates its meaning clearly. If the purpose of language is solely based on arbitrary grammatical rules then idioms, and puns should be discarded at the wayside. But the joke itself is even more fatuous. Since the 1500’s both can and may have had semantic overlap. ^1 Even the current oxford definition of “can”” includes as a secondary definition “have permission to do” ^2 and even the primary definition" be physically or mentally able to” includes this spirit due to the definition of able including “1.b. having the freedom or opportunity to do something ” and 1.a. “having sufficient power, skill, or resources to do something”^3. Given that a student does not have the legal power to allow himself to allow himself to the bathroom the joke seems more and more fatuous.
In this scenario, both parties can understand each other with clarity therefore such a clarification serves as a demonstration of authority rather than correctness. This type of pedantry comes with dangers as it comes with the memorization of unnatural conventions rather than natural usage. Prose written in such form is less expressive and faithful. And a student who changes “can” to "may" demonstrates not an intimate knowledge of grammar but obedience. Without an understanding of the reasoning, he simply tries to guess the correct response through conditioning.[^4]

[^4]: This article describes something similar about guessing the correct password rather thn learning. https://www.lesswrong.com/posts/NMoLJuDJEms7Ku9XS/guessing-the-teacher-s-password