MODAL VERBS

1. auxiliary verb

1.1. CAN

1.1.1. permission

1.1.1.1. You can use my pencils

1.1.2. ability

1.1.2.1. I can read a book in one week.

1.1.3. possibility

1.1.3.1. She can be really sad

1.1.3.2. offer

1.1.3.2.1. Can I do anything for you?

1.1.4. request

1.1.4.1. Can you be quiet?

1.2. COULD

1.2.1. suggestion

1.2.1.1. You could write a letter to your friend

1.2.2. permission (more polite)

1.2.2.1. Could I ask you a personal question?

1.2.3. ability

1.2.3.1. When I was a child I could jump the rope.

1.2.4. possibility

1.2.4.1. He could be one who stole the money.

1.2.5. request (more polite)

1.2.5.1. Could you borrow your pencil, please?

1.3. HAVE TO

1.3.1. obligation

1.3.1.1. I have to wear an uniform in my school.

1.3.2. necessity

1.3.2.1. I have to brush my teeth

1.3.2.2. I have to drink two litters of water