Should, must, mustn’t and have to
A modal verb is followed by the base verb, never by to and never with -s: She should rest, not She shoulds rest. Use should and shouldn’t for advice: You should drink more water. Use must for a strong rule or strong advice that comes from the speaker: You must wear a seat belt. The negative mustn’t means that something is not allowed: You mustn’t shout in the library. Use have to for a rule or a duty from outside: Students have to arrive by eight. For he, she, it we say has to, for the past had to, and for questions Do you have to …? Now notice the contrast. Mustn’t means it is forbidden. Don’t have to means it is not necessary, but it is allowed: You don’t have to wear a coat today, because it is warm. Must is the speaker’s opinion or rule; have to is an outside rule. In a warm invitation, must can also be friendly: You must try my mother’s cake.
| Meaning | Form | Example |
|---|---|---|
| Advice | should / shouldn’t | You should sleep early. |
| Not allowed | mustn’t | You mustn’t run here. |
| No choice (outside rule) | have to / has to / had to | I have to be at school at 7:30. |
| Not necessary | don’t / doesn’t have to | You don’t have to pay. |
Volunteers, listen please. You have to sign your name when you arrive.
Do we have to wear a badge?
Yes, you do. And you mustn’t leave children alone in the reading corner.
Do I have to bring my own lunch?
No, you don’t have to. We provide sandwiches, and you should drink plenty of water.
Thank you. We must come and try the new stories on Saturday!
Class rules. Write six rules for a school library or a youth club. Use should, mustn’t, have to and don’t have to at least once each. Then write a short paragraph of 60 to 80 words that begins “Every good citizen should …” and gives two duties.