Use of have to/must

USE  OF 'HAVE' TO..'MUST

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have to, must

Have to is NOT an auxiliary verb (it uses the verb have as a main verb). We include have tohere for convenience.

Must is a modal auxiliary verb.

have to for objective obligation

must for subjective obligation

must not for prohibition

have to for objective obligation

We often use have to to say that something is obligatory, for example:

• Children have to go to school.

Note that we can use the have to expression in all tenses, for example: he has to, he had to, he has had to, he will have to

Structure of have to

Have to is often grouped with modal auxiliary verbs for convenience, but in fact it is not a modal verb. It is not even an auxiliary verb. In the have to structure, "have" is a main verb.

The basic structure for have to is:

subject

+

auxiliary verb

+

have

+

to-infinitive

Look at these examples in the Present Simple tense:

	subject	auxiliary verb	main verb have	to-infinitive
+	She		has	to work.
-	I	do not	have	to see	the doctor.
?	Did	you	have	to go	to school?

Use of have to

In general, have to expresses impersonalobligation. The subject of have to is obliged or forced to act by a separate, external power (for example, the Law or school rules). Have to is objective. Look at these examples:

• In France, you have to drive on the right.
• In England, most schoolchildren have towear a uniform.
• John has to wear a tie at work.

In each of the above cases, the obligation is not the subject's opinion or idea. The obligation comes from outside.

We can use have to in all tenses, and also with modal auxiliaries. We conjugate it just like any other main verb. Here are some examples:

	subject	auxiliary verb	main verb have	to-infinitive
Past Simple	I		had	to work	yesterday.
Present Simple	I		have	to work	today.
Future Simple	I	will	have	to work	tomorrow.
Present Continuous	She	is	having	to wait.
Present Perfect	We	have	had	tochange	the time.
modal may	They	may	have	to do	it again.

must for subjective obligation

We often use must to say that something is essential or necessary, for example:

• I must go.

Structure of must

Must is a modal auxiliary verb. It is followed by a main verb.
The basic structure for must is:

subject

+

auxiliary verb must

+

main verb base

The main verb is always the same form: base
Look at these examples:

subject	auxiliary verb must	main verb base
I	must	go	home.
You	must	visit	us.
We	must	stop	now.

Like all auxiliary verbs, must cannot be followed by to. So, we say:

• I must go now.
  not I must to go now.

Use of must

Ingeneral, must expresses personalobligation. Must expresses what the speakerthinks is necessary. Must is subjective. Look at these examples:

• I must stop smoking.
• You must visit us soon.
• He must work harder.

In each of the above cases, the "obligation" is the opinion or idea of the person speaking. In fact, it is not a real obligation. It is not imposed from outside.

It is sometimes possible to use must for real obligation, for example a rule or a law. But generally we use have to for this.

We can use must to talk about the present or the future. Look at these examples:

• I must go now. (present)
• I must call my mother tomorrow. (future)

We cannot use must to talk about the past. We use have to to talk about the past.

must not for prohibition

We use must not to say that something is not permitted or allowed, for example:

• Passengers must not talk to the driver.

Structure of must not

Must is an auxiliary verb. It is followed by amain verb.
The basic structure for must not is:

subject

+

must not

+

main verb

The main verb is the base verb.

We often contract must not to mustn't.

Look at these examples:

subject	auxiliary must + not	main verb
I	mustn't	forget	my keys.
You	mustn't	disturb	him.
Students	must not	be	late.

NB: like all auxiliary verbs, must CANNOT be followed by to. So, we say:

• You mustn't arrive late.
  not You mustn't to arrive late.

Use of must not

Must not expresses prohibition - something that is not permitted, not allowed. The prohibition can be subjective (the speaker's opinion) or objective (a real law or rule). Look at these examples:

• I mustn't eat so much sugar. (subjective)
• You mustn't watch so much television. (subjective)
• Students must not leave bicycles here. (objective)
• Policemen must not drink on duty. (objective)

We can use must not to talk about the present or the future:

• Visitors must not smoke. (present)
• I mustn't forget Tara's birthday. (future)

We cannot use must not to talk about the past. We use other structures to talk about the past, for example:

• We were not allowed to enter.
• I couldn't park outside the shop