4-1 Expressing Necessity

I've got to return these books to the library.

Modal Verbs

Modals are auxiliary verbs with special meanings.

can
could
would
should
will
may
might
must
ought (to)
shall

Modals are different from normal verbs. They don't use an s for he / she / it:

He cans go to the store.
He can go to the store.

They make questions by changing the order of the words in the sentence:

She can go.
- Can she go?

They are followed directly by the base form of another verb (without to) (*ought to is the only exception):

He must goes.
He must going.
He must to go.
He must go.

Other Expressions

English has many other expressions used in a similar way to modal verbs:

be able to
be allowed to
be going to
be supposed to
have got to
have to
had better

Expressing Necessity

We can use verbs such as must, have to, or have got to to say when something is necessary:

Children must do their homework.
Children have to do their homework.
Children have got to do their homework.

Be careful of the differences in form:

Example #1

	must	have to	have got to
Positive	He must go to work.	He has to go to work.	He has got to go to work.
Negative	He must not work.	He doesn't have to go to work.	He hasn't got to go to work.
Question	Must he work?*	Does he have to work?	Has he got to work?
*Questions with must are not common.

Example #2

	must	have to	have got to
Positive	You must do your homework.	You have to do your homework.	You have got to do your homework.
Negative	You mustn't do your homework.	You don't have to do your homework.	You haven't got to do your homework.
Question	Must you do your homework?*	Do you have to do your homework?	Have you got to do your homework?
*Questions with must are not common.

Have to, have got to, and must all express that it is necessary to do something. Must is usually stronger in meaning and can express urgency or importance:

I have to go home.
I've got to go home.
I must go home. (stronger in meaning)

Because must has a stronger meaning, it is less common in spoken English when describing necessity. English speakers usually prefer have to or have got to. Must is more common in writing.

There is no past form of must or have got to. Instead, use had to:

I must study.
I have to study.	I had to study. (past)
I have got to study.

Lack of Necessity

To say that it isn't necessary to do something, we use do not have to or have not got to. To talk about the past, we use did not have to:

The concert is free. You do not have to pay to enter.

I don't have school tomorrow. I don't have to go to bed early tonight.

We haven't got to hurry. There's still lots of time.

Last night, I didn't have to make dinner because my mother took me out to a nice restaurant.

Jane didn't have to do any homework because she had finished everything during class.

Prohibition

Using must in the negative has a very different meaning. It means that something is prohibited. This means you cannot do it, you are not allowed to do it, or it is bad to do it: