You needn't say it again. We don't have to write this essay. He hasn't got to leave now

2. The verb must is used to express commands, orders, urgent and emphatic requests and suggestions. It is followed by the indefinite infinitive only and doesn’t change according to the rule of the sequence of tenses:

You must leave the room at once.

You must visit us as soon as possible.

He said we must leave the room at once.

3. The negative form of must is used to express prohibition that is rather a command or an order not to do something. The indefinite infinitive of the notional verb is used:

Visitors must not feed animals at the zoo.

You must not discuss this question now.

4. The verb must is used in affirmative statements to express supposition (speculation), implying strong probability, bordering on assurance or almost a conviction. As the modal verb must has only one form, the form of the infinitive of the notional verb expresses the time reference. Indefinite and non-perfect continuous infinitives refer the action of the notional verbs to the present, while perfect infinitives refer the action of the notional verb to the past:

You must know her as she was in your group. They must be waiting for us.

They must have heard the news already.

When the action expressed by the notional verb refers to the present we often use the continuous infinitive to avoid ambiguity:

He must work hard. He must be working hard.

We usually don’t use the negative form of the infinitive after the verb must to express supposition. Modal words and phrases are used instead:

He is not likely to come today.

Probably, he didn't know about your arrival.

The verb must is not used to express supposition about future actions, but modal words and phrases are:

He will evidently come at nine. It's likely to rain tonight.

5. The phrase ‘ if you must ’ is used when you allow something you don't approve of:

If you must talk, do it outside please.

HAVE (TO)

The verb have to is a semi-modal verb and it has a full morphological paradigm. It forms interrogatives and negatives with the help of auxiliary verbs as all notional verbs do:

Do you really have to stay there so late?

He didn't have to tell us the news. We knew it already.

The verb have to can express the following meanings:

1. The verb have to is used to express necessity or obligation arising out of circumstances. The phrase have got to can be also used to express necessity or obligation referring to the present:

I've missed the train, now I'll have to wait for the next one.

I've got to go by train; there is no other way to get there.

I have to go there by train. I had to hurry to catch the train.

2. The verb have to is used to express absence of necessity in negative sentences. The phrase have got to can be used if the situation refers to the present:

I don't have to go there because they have telephoned.

I haven't got to go there.

I didn't have to wait long at the doctor's yesterday.

You won't have to do anything there.

3. The verb have to is used to give instructions and recommendations when telling how to do something:

You have to mix flour and butter first.

Sometimes these sentences may sound like advice.

4. The verb have to is used in affirmative statements to express supposition (speculation) implying strong probability when you are sure that something is happening or will happen:

There has to be an answer to this question.

The price of houses has to go up sooner or later.

BE (TO)

The verb be to is a semi-modal verb. Its present and past forms can express modal meanings.

1. The verb be to expresses obligation or necessity arising out of arrangement or plan. The non-perfect forms of the infinitive are used: