A OBLIGATION • We use the modal verb MUST for indicate that is necessary to something Ex I must my homework • The negative MUSTN’T is used for indicate that we’re not allowed to something Ex I musn’t drink cola • The verb MUST doesn’t change with he/she/It We always follow this structure: Subject + (Modal Verb) + vb (infinitive) without TO • We can also use the modal verb HAVE TO for indicate obligation and all its forms (don’t have to , had to, has to ) • Must and Have to have very similar meanings They both mean something is necessary • We usually use have to for talking about rules and laws • REMEMBER! The negative form of have to and must is very different (don’t have to and mustn’t) Other verbs that can give us obligation are HAD TO and COULD • In negative statements COULD (the past simple of CAN) is COULDN’T and HAD TO is DIDN’T HAVE TO (it follows the past simple tipical structure • We also use COULD for talking about ability in the past We use COULDN’T when we have to talk about something that we weren’t able to B PRACTICE B.1- Complete the sentences Use the modal verbs 1) They _ arrive on time to work 2) They be rude to the public 3) They _ wear an uniform 4) They _ careful with us 5) When I was 5, I _ walk, but I swim 6) They _ study science B.2- Choose the correct verbs 1) You mustn’t/don’t have to study law to be a forensic scientist 2) I must/mustn’t spend some time with my parents I haven’t seen them for ages 3) We mustn’t/don’t have to commit crimes 4) You must/have to take the passport for travelling to South Africa 5) I couldn’t / mustn’t swim when I was years old 6) You must/could check your answers for avoiding errors 7) I had to/could drank water, but I couldn’t/didn’t have to drink beer B.11) 2) 3) 4) 5) 6) B.21) 2) 3) 4) 5) 6) 7) have to don’t have to must have to mustn’t must don’t have to must don’t have to have to couldn’t must had to/couldn’t