This document discusses modal verbs used to express obligation and necessity. It explains: 1) "Have to" is used to talk about rules, obligations, or things that are necessary. 2) "Must" is also used to talk about rules and obligations, and only has the forms "must" and "mustn't". 3) "Must" indicates obligation from the speaker, while "have to" can indicate obligation from another person. 4) "Don't have to" means there is no obligation or necessity, while "mustn't" expresses prohibition.

1. MODAL VERBS (I): Must, have to, don’t have to, mustn’t p. 134

7. OBLIGATION FROM THE SPEAKER FROM ANOTHER PERSON I must go to bed. I’m exhausted. I must remember to phone her tomorrow – it’s her birthday. You have to wear a seatbelt in the car. Do you have to work on Saturdays? I had to wear a uniform when I was at school.