S 'can' in 'may' nekomu dovoljuješ, da nekaj stori.

can/can't - navadna raba (v družini in med prijatelji)

You can borrow my pen if you want. 
You can't watch television.

may/may not - uradna in zelo vljudna raba (do neznancev)

Excuse me, may I sit here? 
Passengers may not smoke.