Modal Verbs | Should – Must – Have to | In English Grammar

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In this lesson, I will answer all those questions you have asked yourself about these modal verbs.
In this concept, we will concentrate on the difference between the modal verbs MUST, SHOULD, and HAVE TO.
This article is for those who wish to clear up doubts about this topic.

Should and Must are modal verbs and therefore, like all model verbs:

Both are always followed by the infinitive ‘without to’:

Should do, must do,

They are the same for all the pronouns:

I should, She should, He should, it should, etc.

So, let’s get to the bottom of this.


1.Expressing thinking (opinion) / Giving suggestions (advice) or asking for advice.

For example,

  • I believe Engineers should have higher salaries.
  • You look exhausted. I think you should have some rest.
  • What should I say when I speak to him?
  • Do you think we should phone him?

2. Expressing an expectation

For example,

  • She should arrive by now.
  • He should arrive any minute.

3. Expressing regret about a past action

For example,

  • You should have been more careful.
  • We shouldn’t have said that.


Must refer to express strong obligation with which the speaker agrees.
and it indicates a necessity.

For example,

  • She is very ill. You must call a doctor now.
  • This is the best book I’ve read. You must read it too.

2. Expressing a prohibition ( present or future)

For example,

  • You must not (mustn’t) open it until you get home.
  • You must not be late for your exam tomorrow.

3. Expressing an assumption (guessing/ expectation) in the present or past

For example,

  • We think everthing must be destroyed and all the girls are dead.
  • She must have read my diary, because she repeated exactly what I had written.

Have to

1. Expressing an external obligation (positive sentences)

For example,

  • You have to make an appointment too see Miss Tina.
  • He has failed his test. He has to retake it.

2. Expressing a need or obligation in the past

For example,

  • She was very ill. We had to call the doctor immediately.
  • John was very busy. We had to make an appointment to see him.

3. Removing a need or an obligation (present, past, future)

For example,

  • She feels much better now. You don’t have to call a doctor.
  • She didn’t have to make an appointment to see Rahul.
  • He has passed his exam. He won’t have to retake it.
'Need to' is a swampy (softer) substitute (alternative) to both 'must' and ' have to:

I must/need to finish this task tonight, because I want to take tomorrow off.

I have to/need to finish this tonight. My deadline is tomorrow.

Click here to practice  MUST, SHOULD, and HAVE TO Quiz

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