Modal verbs of Obligation
Sometimes students struggle with modal verbs and their different uses. Some modal verbs can be used to express different functions, so, when do we know which ones to use?
We use have to + infinitive, must + infinitive and should + infinitive to express obligation (something you have to do)
Have to and must
These are normally used to talk about obligation or something that it is necessary to do and is a strong obligation.
*You have to wear a seatbelt in a car.
*You must remember to phone Emily.
What is the difference between have to and must?
They have a very similar meaning and you can usually use either form.
Have to is more common for general, external obligations for example rules and laws
- I have to wear a shirt and tie at work
Must is more common for specific or personal obligations for example on one occasion.
- I must buy a new shirt
Have got to is often used instead of have to or must in spoken English
- I’ve got to go now. It’s very late.
Don’t have to and Mustn’t
Don’t have to and mustn’t are completely different.
*You don’t have to pay, this museum is free.
*You mustn’t park here.
We use don’t have to when there is no obligation to do something.
- You don’t have to get the train we can drive.
We use mustn’t when something is prohibited.
- You mustn’t smoke inside.
Can’t or not allowed to are often used instead of mustn’t.
Should and shouldn’t
Should is not as strong as must/have to. It is used to give advice or an opinion – to say if we think something is right or wrong thing to do.
Should is a modal verb so the only forms are should / shouldn’t
- You should take warm clothes with you to Dublin.
- You shouldn’t drink so much coffee, it isn’t good for you.
Ought to / ought not to can be used instead of should / shouldn’t
*You ought to take warm clothes with you to Dublin.
*You ought not to drink so much coffee.
If you have any questions regarding modal verbs just ask your teacher they will be happy to help!