5A: must/ have to / can

5A: must/ have to / can

When do we use must ​/ have to/ can?

Multiple Choice

What are these examples?:

Visitors must wash their hands.

We have to wash our hands.

• Not allowed to do something, a rule

• Necessary to do something,

  a rule

• Allowed to do something

• Not necessary to do something

Multiple Choice

What are these examples?:

You mustn’t smoke in the building.

We can’t smoke here.

• Not allowed to do something, a rule

• Necessary to do something, a rule

• Allowed to do something

• Not necessary to do something

Multiple Choice

What is this example?:

You can smoke outside.

• Necessary to do something, a rule

• Allowed to do something

• Not allowed to do something, a rule

• Not necessary to do something

Multiple Choice

What is this example?: 

You don’t have to wear a uniform.

• Allowed to do something

• Necessary to do something, a rule

• Not allowed to do something, a rule

• Not necessary to do something

​Must and have to have very similar meanings.

​Must

​Must is often used in written rules:

​

• ​All patients must wash their hands.

Open Ended

Can you give us an example of a written rule?

​Must

​People in authority use must when they are speaking, for example, teachers, parents etc.:

​

• ​You must switch off your mobile phones.

Open Ended

Can you give us an example of a person of authority? 

​Have to

​We use have to when we say what is necessary. It is very common in spoken English:

​

• ​Doctors have to work very long hours.

• ​I have to leave for work at 7. 00 am.

Open Ended

Can you give us an example to say something that is necessary?

​Must not and don’t have to have very different meanings.

​Must not

​Must not means something is not allowed — it is important not to do something:

​

​- Students must not talk in the exam room.

​- You mustn’t smoke in here.

Open Ended

Can you give us an example of something that is important NOT to do? (something not allowed)

​Don't have to

​Don ’t have to means something is unnecessary:

​

​- Teachers don’t have to wear a uniform.

​- He doesn’t have to work because he’s rich.

Open Ended

Can you give us an example of something that is unecessary?

​Can

​Can means something is allowed:

​

​- You can take a one—hour lunch break.

​- You can borrow up to five books from the library.

Open Ended

Can you give an example for when something is allowed?

​Can’t is similar to Mustn’t.

​It means not allowed / not possible:

​

​ - You can’t smoke here.

​ - Bankers can’t relax for a minute.

Open Ended

Can you give an example for when something is not allowed or not possible?

The End​

Complement with exercises in Grammar Focus 5A. ​P. 151.