Modal verbs (and other verbs) to express OBLIGATION

Hello Everyone! Today we are looking at the verbs used to express obligation.

Must, should and ought to are the modal verbs used to express obligation. Ought to has exactly the same meaning as should but is not commonly used. Have to, which is a full verb, is also used to talk about obligation. Examples of statements, questions and negatives:-

  1. Tom must help Kathy.
  2. Must Tom help Kathy?
  3. Tom mustn’t help Kathy.
  1. Tom should help Kathy.
  2. Should Tom help Kathy?
  3. Tom shouldn’t help Kathy.
  1. Tom has to help Kathy.
  2. Does Tom have to help Kathy?
  3. Tom doesn’t have to help Kathy.

Must and have to are both used to talk about STRONG obligation.

Modal verbs (and other verbs) to express Obligation 1

Must is used when the speaker uses his/her authority and cares about the obligation being spoken about.

Example

Mother: “Emma, you must do your homework!” Emma’s mother is using her authority as Emma’s parent and wants her to do her homework. It is 100% important that Emma should do her homework.

Have to is used to express general obligation. The speaker has no authority over the person being spoken to.

Example

Friend: “Emma, you have to do your homework!” Emma’s friend has no authority over her, she can’t make her do her homework but, still, the obligation is 100% strong. Have to is often used to talk about rules or laws. E.g. In India, you have to drive on the left.

Must doesn’t have a past form, so the past of must and have to is had to. You can’t show if the speaker used his/her authority or if the obligation was general.

Example

He must do his homework. (Present)
He had to do his homework. (Past)

He has to do his homework. (Present) He had to do his homework. (Past)

Mustn’t and don’t have to have completely different meanings in the negative.

Mustn’t means forbidden and don’t have to means no obligation but you can if you want to.

Example 1.
“You mustn’t play with fire!” You are forbidden from doing this – You could get burnt. You wouldn’t say “You don’t have to play with fire” because that would mean that you can if you want to!

Example 2.
“You don’t have to help me with the cooking” There is no obligation but you can if you want to. (I may like some help). “You mustn’t help me with the cooking” means I forbid you from helping me. I really don’t want your help!

The past of don’t have to is didn’t have to. It has exactly the same meaning as don’t have to but in the past, i.e. there was no obligation but you could if you wanted to. E.g. When I was young I didn’t have to help my mother with the cooking but, if I finished my homework early, I sometimes did.

The past of mustn’t is wasn’t allowed to which means was forbidden from… E.g. “When I was young I wasn’t allowed to play with fire” means “When I was young I was forbidden from playing with fire.”

Should is used for mild obligation and advice.

Example

“You should do your homework.” It is the right thing to do and I advise you to do it.

The negative of should is shouldn’t as;

“You shouldn’t go to bed too late.” I advise you not to.

The past of should is should have. It means you didn’t do something but it would have been the right thing to do.

Example

“You should have learned for the test” – unfortunately, you didn’t.

Shouldn’t have means that you did something but it was the wrong thing to do.

Example
“You shouldn’t have eaten all the pizza” – you did and it was the wrong thing to do!

To test your understanding of verbs of obligation, try grammar quiz as follows:

Grammar Quiz

Modal verbs (and other verbs) to express Obligation 2

See how much you understand about using verbs of obligation! Circle the correct sentence, A or B.

1.

A. Does he have to come to the meeting?

B. Has he to come to the meeting?

2.

A. You mustn’t drink poison!

B. You don’t have to drink poison!

3.

A. You don’t have to come shopping with me but you can if you want to.

B. You mustn’t come shopping with me but you can if you want to.

4.

A. Doctor “You have to take this medicine three times a day for a week.”

B. Doctor “You must take this medicine three times a day for a week.”

5.

A. Friend “You must pay your school fees!”

B. Friend “You have to pay your school fees!”

6.

A. When I was young I must help my mother clean our house.

B. When I was young I had to help my mother clean our house.

7.

A. Jim failed the exam! He should have studied harder!

B. Jim failed the exam! He had to study harder!

8.

A. Anna didn’t has to buy me a present!

B. Anna didn’t have to buy me a present!

9.

A. In India most school children must wear a uniform.

B. In India most school children have to wear a uniform.

10.

A. You mustn’t drive over the speed limit!

B. You don’t have to drive over the speed limit!

Answers: 1A, 2A, 3A, 4B, 5B, 6B, 7A, 8B, 9B, 10A

Modal verbs (and other verbs) to express Obligation

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