must / have to / should

Rules

• Rule 1: must and have to = necessary

  must and have to mean something is necessary. must never changes. have to becomes has to with he / she / it.

  Pattern: subject + must / have to / has to + base verb

  Example: We must listen to the coach.

  Example: My mom has to get up at six.

• Rule 2: mustn't = not allowed!

  mustn't (must not) means “Don't do it! It's against the rules.” In everyday American English, people often say can't instead: You can't swim here.

  Pattern: subject + mustn't + base verb

  Example: You mustn't swim here. It's dangerous.

  Example: We mustn't eat in the classroom.

• Rule 3: don't have to = not necessary

  don't have to means “you can do it if you want, but you don't need to”. It is NOT a rule against something. With he / she / it: doesn't have to.

  Pattern: subject + don't / doesn't have to + base verb

  Example: You don't have to bring a pencil. I have one.

  Example: Ela doesn't have to go to school today.

• Rule 4: should / shouldn't = advice

  should gives advice: “it's a good idea”. shouldn't means “it's not a good idea”.

  Pattern: subject + should / shouldn't + base verb

  Example: You should wear a coat. It's cold.

  Example: You shouldn't stay up so late.

Common mistakes

• You must to go. → You must go.

  No to after must or should.

• She have to study. → She has to study.

  she → has to.

• Does he has to go? → Does he have to go?

  After Does, use have.