Modal Verbs of Obligation and Necessity English Learners

 Use of Modal Verbs of Obligation and Necessity

Modal Verbs can be used to talk about obligation, freedom and necessity to do something. We use the following modal verbs:
Must, Have to, Need to, Don’t have to, Needn’t, Don’t Need to + infinitive

 . Talking about Obligation and Necessity in the present

  Obligation
Have to and must are both used to express obligation. There is a slight difference between the way they are used
Have to shows us that the obligation comes from somebody else. It’s a law or a rule and the speaker can’t change it

In Britain you have to wear a seat belt when you drive

Must shows us that the obligation comes from the speaker. It isn’t a law or a rule
I must finish this before I go home
Sometimes if the speaker agrees with an external rule they will use must

In Britain you must wear a seat belt when you drive

 Need to have to and need to are often used in the same context, but many times, need to is used to express something that is less urgent, something in which you have a choice

I have to work late tonight

I need to work late tonight

 Forbidden

If something is forbidden must not / mustn’t + base form of the verb

You must not drive drink and drive

You mustn’t leave medicines where children can find them

   No obligation
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.
don’t /doesn’t /didn’t + have to + base form of the verb

You don’t have to wear a tie in our office. You can wear a tie if you want to but it’s OK if you don’t
needn’t + base form of the verb

You needn’t worry about me. I’ll be fine

 .Talking about Obligation and Necessity in the past

There is no past form of must so we use had to

had to / needed to + base form of the verb

I had to work late last night
I needed to drink a few cups of coffee in order to stay awake
Note: have to and need to are often used in the same context, but many times, need to is used to express something that is less urgent, something in which you have a choice

 .Talking about Obligation and Necessity in the future

There is no future form of must so we use have to

will have to / will need to + infinitive

I will have to work late last night

I will need to drink a few cups of coffee in order to stay awake