B1 · Lesson 10 · 20 min
Obligation, prohibition and permission
In this lesson
- I can describe rules and obligations using must, have to and need to.
- I can say what is prohibited or permitted using mustn't, don't have to and be allowed to.
Grammar in context
Maya has started a weekend job at a city museum. Staff must wear an ID badge, and visitors mustn't touch the paintings. Maya does not have to work every Saturday, but she needs to tell her manager early if she cannot come. She is allowed to take photos only in the staff room.
Which phrase means that something is necessary, and which phrase means that something is forbidden?
Obligation: must, have to and need to
Use must, have to and need to when something is necessary. Must often expresses a strong instruction or a written rule. Have to is common for rules set by an organisation or situation. Need to is another common way to describe something necessary. The patterns are must + base verb, have/has to + base verb, and need/needs to + base verb.
- You must show your ticket at the entrance.
- Leo has to wear safety shoes at work.
No obligation and prohibition
Don't have to means something is optional: you can do it, but it is not necessary. Mustn't means something is prohibited: do not do it. These meanings are very different. Use don't or doesn't with have to, depending on the subject. Do not use mustn't when you mean that there is no need to do something.
- You don't have to bring food; the café is open.
- Passengers mustn't leave bags near the door.
Permission: be allowed to
Use be allowed to when a rule says that someone can do something. Change be for the person and time: am, is, are, was or were. For questions, put be before the subject: Are we allowed to...? For a negative permission rule, use not allowed to. This is often clearer than can when you are discussing official rules.
- Students are allowed to use the library after school.
- Was I allowed to park behind the building?
Common mistakes
Compare the incorrect and corrected forms.
Avoid
When travel is free: You mustn’t pay for the bus today.
Use
When travel is free: You don’t have to pay for the bus today.
Mustn't means payment is forbidden; don't have to means payment is unnecessary.
Avoid
Are visitors allowed take photos?
Use
Are visitors allowed to take photos?
After allowed, use to before the base verb.
Put it into practice
Try the exercises, write your own examples and check your understanding.