Can vs. May
‘Can’ and ‘May’ are often used interchangeably, but they do have different flavors of meaning worth recognizing.
Generally speaking, ‘can’ means having the ability to do something, and ‘may’ means having the permission to do something. “You can drive this car” means that you are able to operate the vehicle. “You may drive this car” means that you have the blessing to do so.
However, what makes this whole thing a massive clusterfuck is that each of the words individually have multiple meanings.
‘Can’ often is used to mean having permission. Any normal person who says “You can drive my car” is clearly granting permission; it is a universally understood speech pattern, which makes it grammatically correct. Similarly, any normal person who asks, “Can I borrow your car” is clearly asking for permission; the only people who say “I don’t know, can you” are assholes.
‘May’ becomes more problematic because its secondary meaning is that an action is uncertain. “I may drive my car” means that there is a chance that I will drive my car, but there is also a chance that I won’t.
What is most amazing here is that we as English speakers pretty much always understand which meaning of which word is intended solely by the context in which it is said. However, some situations do allow for ambiguity, and some people thrive on using ambiguity or dual meanings to screw with others, so these words can be problematic in use.
Again, although people know how to use these words latently, it is valuable to know the differences and understand the subtle implications of using one word versus another.