A student recently asked me what the difference between "Can" and "Could" is. Here is an explanation: CAN OFFER: Can I help you? PERMISSION (give and ask) You can put it over there. ABILITY (present) I can drive a car. POSSIBILITY She can be really sad. REQUEST Can you be more direct with your answer? COULD (more polite) SUGGESTION We could write an email to the CEO. PERMISSION Could I ask you a personal question? ABILITY (past) When I was a child, I could speak German. POSSIBILITY He could be the one who stole the money. REQUEST Could I borrow your pencil please? I hope that gives you the explanation.