modal verbs

modal verbs II

prohibition, obligation

Obligation

We use have to and must to express obligation.

There is a slight difference between the way we use them.

have to

Have to shows us that the obligation comes from outside the speaker. 

We sometimes call this 'external obligation'.

We have to wear a uniform when we're working in reception.

(Student to teacher) When do we have to hand in our homework?

Alex has to work tomorrow so he can't come.

must

Must expresses a strong obligation or necessity. It often shows us that the obligation comes from the speaker (or the authority that wrote the sentence). 

Note that we don't use must to express obligation in the past. We use have to instead.

I had to pay £85 to renew my passport last week.

No obligation

don't have to

We use don’t have to to show that there is no obligation. You can do something if you want to but it's not compulsory.

You don't have to wear a tie in our office but some people like to dress more formally.

You don't have to go to the bank to do a transfer. You can do it online.

You don't have to come with me, honestly. I'll be fine!

Multiple Choice

What does this sign say? Oh, we ________ park here.

• should

• can

• can't

• ought

Multiple Choice

You ______ take photos in the museum. They're really strict about it.

• can't

• should

• ought

• have to

Multiple Choice

Visitors _____ not park in the staff car park.

• should

• can

• must

• have to

Multiple Choice

Baggage ___________ be left unattended.

• have to

• can

• must

• musn't

Multiple Choice

We ________ wear a uniform when we're working in reception.

• have to

• must

• can

• hope

Multiple Choice

Alex ______ work tomorrow so he can't come

• have to

• has to

• must

• can

I must phone my dad. It's his birthday today.

(Teacher to student) You must hand in your homework on Tuesday or you will lose ten per cent of your mark.

(Sign on a plane) Seat belts must be worn by all passengers.