Modals of Obligation

This page will teach you when and how to use modals of obligation and prohibition


We use modals of obligation to describe necessity or the lack of it. Whereas modals of prohibition are used say that something is not permitted or against the rules.

Present / Future

We can use the following structure with must to describe obligation when the obligation comes from within.


must(n’t)

+

infinitive


I must study for my exam tomorrow.

You mustn’t smoke here.


We can use the following structure with have/has to to describe obligation when the obligation comes from outside.


Have/Has to

+

infinitive


His boss says that he has to be at work on time

They have to finish their project by tomorrow.


* Note: We can use have got to, in a similar way.


They've got to finish their project by tomorrow.


* Note: We can use need to in a similar way.

She has to work long hours to pay off her loan.

She needs to work long hours to pay off her loan.


We can use the following structure with don’t/ doesn’t have to to describe lack of obligation.


Don’t/Doesn’t have to

+

infinitive


He doesn’t have to wear a suite at work.

We don’t have to be at the airport for another hour.


* Note: We can use don’t / doesn’t need to or need not/needn’t in a similar way.

We don’t need to be at the airport for another hour.

We needn’t to be at the airport for another hour.


Past

We can use the following structure with had to to describe obligation when the obligation comes from outside.


Had to

+

infinitive


We ran out of gas, so we had to walk to the gas station.

They did a terrible job and had to redo everything.


* Note: We can use needed to in a similar way.

She had to show her passport at customs.

She needed to show her passport at customs.


We can use the following structure with didn’t have to to describe lack of obligation.


Didn’t have to

+

infinitive


He didn’t have to bring camping equipment because it was all provided.

They didn’t have to bring any food to the party.


Future

We can use the following structure with will have to to describe obligation in the future.


Will have to

+

infinitive


He will have to study all weekend if he wants to pass the exam on Monday.

Note: We can use going to instead of will.

They missed their train, so will have to wait until the next train.

They missed their train, so are going to have to wait until the next train.


We can use the following structure with will not/ won’t have to to describe lack of obligation in th future.


Will not/Won’t have to

+

infinitive


She won’t have to visit her grandparents for their anniversary as they are spending it abroad this year.

Note: We can use going to instead of will.

She isn’t going to have to visit her grandparents for their anniversary as they are spending it abroad this year.