PAST OF MODALS p. 42 world pass Student's book

P R E S E N T P A S T
ability: can could
giving permission: can/may could/was-were allowed to
necessity: must/have had to was, were required to
lack of necessity: dont/doesn't have to didn't have to
advice/regret: should should have
negative should't shouldn't have

examples:
I can play guitar (present) She could play guitar at age 8
She may go the party. She was allowed to go to the party
She must attend to the meeting He eas recquired to go to the meeting
They have to go to the airport first They had to go to the airport first.
You don't have to do all the exercises p.10 You didn't have to do all the reading.
Mary should take some medicine now. She should have taken some medicine
Charlie shouldn't make so much noise. He shouldn't have made so much noise.