CAN
A. Ability, Power and Capacity
1. Ravi can drive a car.
2. Can you lift this weight?
3. He can speak English fluently.
4. They can not help at this time.
B. To Give or Take Permission (informal)
1. Can I take your pen?
2. You can go now.
C. Possibility (Mostly used for negative and interrogative sentences)
1. This news can not be true.
2. He can not come today?
3. Can he be angry?
COULD
A. Ability, Power and Capacaity in Past
1. He could drive a car.
2. They could win this competition.
3. He ran as fast as he could.
B. Permission/Possibility in Past
1. He asked me if he could take my pen.
2. He told her that he could not give her his car.
C. Use in Present (More polite and hesitant than can)
1. Could you give me your pen?
2. Could you tell me the way to the railway station ?
SHOULD
Duty, Advice etc.
1. You should meet him tomorrow.
2. Should we attend the function?
SHOULD HAVE
1. He should have played the match.
2. Should they have told a lie?
MUST
Must is used to express Duty, Necessity etc.
1. You must go to school daily.
2. You must work hard if you want to succeed.
"Be" is used in place of verb or while adding "ing" with a verb. It is a use in present, not future.
1. She must be in the office.
2. You must be sixteen.
3. Rajat must be sleeping.
4. Teacher must be teaching the class.
