Student: Aha, but I clearly meant to ask for permission. Since you and the rest of the class understood my intent perfectly well, and the word “may” to show permission is rapidly falling out of fashion, there is nothing wrong with asking you whether I can borrow a pencil.
Teacher: Possibly so, in colloquial speech. Discerning context can help us decipher the nuance of each sentence on a case-by-case basis. However, as your teacher, my task is...
...to teach you the intricacies and nuances of the English language with rigor, so that you may have a greater mastery of the language in order to effectively and precisely control what you want to communicate. In this case, the difference between the words “can” and “may”.
I have a personal beef with teachers that do this. In 2nd grade I asked “can I please go to the bathroom”. Teacher said no until I asked properly. I asked again a minute later and twice more within a few minutes. Each time with the same answer. I then wet my pants and peed all over my chair. She let me go to the bathroom then. [emo1848]
Everyone knows teachers buy and supply the pencils themselves. Which sucks. I also hate this ambiguous crap, no need to make students waste your time over something that trivial.
Student: Can I borrow a pencil?
Teacher: I don’t know, can you borrow a pencil?
Teacher: No, you may not. The state cut funding for education again.