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MUST & HAVE TO & MUSTN'T & DON'T HAVE TO (MODAL VERBS)

Updated: Sep 24

MUST & HAVE TO & MUSTN'T & DON'T HAVE TO (MODAL VERBS)

GRAMMAR


must / might / may / can't / couldn't + have + past participle


rules

examples

We use must have when we are almost sure that something happened or was true.

must have left my phone at Anna's. I definitely remember having it there. 

You must have seen something. You were there when the accident happened.

We use might / may have when we think it's possible that something happened or was true.



We can also use could have with this meaning.

Somebody might have stolen your wallet when you were getting off the train. 

He still hasn't arrived. I may not have given him the right directions.

Somebody could have stolen your wallet when you were getting off the train.

We use can't have when we are almost sure something didn't happen or that it is impossible.



We can also use couldn't have when the speculation is about the distant past

You couldn't have seen their faces very clearly.

She couldn't have gone to bed. It's only ten o'clock.

You can't have seen it because it doesn't exist.

should have / ought to have + past participle

• Use should have + past participle to say that somebody didn't do the right thing, or to express regret or criticism.

• You can use ought to have as an alternative to should have, 

e.g. I ought to have told you earlier.


 


should / shouldn't (+ infinitive) vs Ought to (+ infinitive)


I ought to marry Kate because I truly love her. 

It should be difficult to live in a foreign country. 

You shouldn’t / oughtn’t to say things like that to granddad. ( I don’t think you ought to say things like that to granddad).)

The girls should / ought to be working now.

 



MUST & HAVE TO & MUSTN'T & DON'T HAVE TO (MODAL VERBS)


GRAMMAR

 have to or must?

Compare:

I have to wear a shirt and tie at work. (= It's the rule in this company.)

I must buy a new shirt - this one is too old now. (= It's my own decision.)


have got to

Have got to is often used instead of have to or must in spoken English, e.g. I've got to go now. It's very late.

MUST

Meaning: "Must" is used when the obligation or necessity comes from the speaker. The speaker believes it is necessary.

When we use "must," the speaker themselves believes something is necessary. The sense of obligation is personal. The speaker feels strongly that the action needs to be done, but it’s not necessarily imposed by an external rule or authority.


  • Example 1:"You must finish your homework before going out."(The speaker thinks it is important to complete the homework.)

  • Example 2:"I must call my parents today."(The speaker feels it's important and necessary.)

  • Example 3:"We must wear a helmet while riding a bike."(The speaker thinks it is essential for safety.)

  • Example 5:"I must go to the gym today."(The speaker feels personally responsible for going to the gym.)

  • Example 6:"You must tell him the truth."(The speaker believes it is necessary for the listener to be honest.)

  • Note: Must is often used for rules or laws that apply to everyone when spoken by someone with authority.For example:"You must wear a seatbelt." (General rule but also reflects the speaker's belief that it’s important.)




HAVE TO (Modal Verbs)

Meaning: "Have to" expresses an external obligation. The necessity comes from an outside source, like rules or another person’s expectations.

"Have to" indicates that the obligation or necessity is imposed by an external factor, such as a rule, law, someone else's instructions, or circumstances that are outside of the speaker’s control.


  • Example 1:"I have to be at work by 9 AM."(The obligation comes from your boss or workplace policy.)

  • Example 2:"We have to submit the project by Friday."(This deadline is set by someone else, not the speaker.)

  • Example 3:"She has to visit the doctor for a check-up."(The obligation comes from the doctor's recommendation.)

  • Example 4:"I have to go to work at 8 AM."(The obligation comes from the workplace’s rules.)

  • Example 5:"She has to finish the report by tomorrow."(The obligation comes from a deadline set by her boss.)

  • Important: Even if the speaker doesn't personally agree with the necessity, "have to" expresses an external requirement.




 

Comparison of MUST vs. HAVE TO (Modal Verbs)

Internal vs. External Obligation

  • Must: Internal/personal obligationExample:"I must exercise more."(The speaker believes they need to exercise more for their own health or fitness.)

  • Have to: External obligationExample:"I have to exercise because my doctor told me so."(The obligation comes from the doctor's recommendation.)

Present Tense Use

In the present tense, must and have to are often used interchangeably, but the distinction lies in the source of obligation:

  • "Must" is when you think it’s important.Example:"I must clean my room."(It’s my own belief that cleaning is necessary.)

  • "Have to" is when someone else or an external rule makes it necessary.Example:"I have to clean my room before my parents arrive."(This obligation comes from my parents or the situation.)

Past Tense Differences

In the past tense, we don’t use "must." We use "had to" to express past obligations, whether personal or external.

  • Example:


    "I had to finish the report yesterday."


    (This was an external obligation.)



 

MUSTN'T (Modal Verbs)

Meaning: "Mustn't" indicates a prohibition. It means that something is not allowed, and it's necessary that you do not do it.

When we use "mustn't," we are saying that it is essential not to do something. This expresses a strong prohibition, often a rule or law, and means that doing the action would be wrong or harmful.


  • Example 1:"You mustn't talk during the exam."(It's forbidden, not allowed during the exam.)

  • Example 2:"We mustn't enter the building after 10 PM."(There’s a strict rule that prohibits entry after 10 PM.)

  • Example 3:"He mustn't use his phone at work."(It’s against the rules to use a phone while working.)

  • Example 4:"You mustn't touch that! It’s dangerous."(Touching it is prohibited because it’s dangerous.)

  • Example 5:"We mustn’t forget to submit the application on time."(Forgetting to submit the application is forbidden, as it would cause problems.)


DON'T HAVE TO (Modal Verbs)

Meaning: "Don't have to" is used when there is no obligation. You can do something if you want to, but it's not necessary.

"Don’t have to" tells us that there’s no need to do something, but doing it is not forbidden. You can choose to do it if you want to, but it's not required.

  • Example 1:"You don’t have to come to the meeting if you’re busy."(You can come if you want, but it’s not necessary.)

  • Example 2:"I don’t have to wear a uniform at work."(There’s no rule that requires the speaker to wear a uniform.)

  • Example 3:"They don’t have to finish the report today."(It's not necessary to finish it today.)



 

Comparison of MUSTN'T vs. DON'T HAVE TO (Modal Verbs)

  • Mustn't: Prohibition, something is not allowed.Example:"You mustn’t smoke in this building."(It’s against the rules to smoke here.)

  • Don’t have to: No obligation, something is not necessary.Example:"You don’t have to smoke."(You’re not required to smoke, but you could if allowed.)


Summary Table

Phrase

Type of Obligation

Example

Must

Internal or personal

"I must study for the exam."

Have to

External

"I have to submit this report by Friday."

Mustn't

Prohibition (Not allowed)

"You mustn’t park here."

Don't have to

No obligation (Optional)

"You don’t have to attend the meeting."

 

Additional Examples for Practice: (Modal Verbs)

  1. Must:"I must apologize for being late."(The speaker feels it is important to apologize.)

  2. Have to:"I have to wear a uniform at my job."(The rule comes from the workplace, not the speaker.)

  3. Mustn't:"You mustn't use your phone during the flight."(It is prohibited by flight regulations.)

  4. Don't have to:"You don’t have to bring food to the party."(It’s not necessary, but you can if you want to.)


 



Comparison Examples

  • MUST vs. HAVE TO:

    • Must:


      "I must call Sarah today."


      (The speaker feels personally that this is necessary.)

    • Have to:


      "I have to call Sarah because she left me a message."


      (The obligation comes from Sarah’s message.)




  • MUSTN'T vs. DON'T HAVE TO:

    • Mustn't:


      "You mustn't park here."


      (It's prohibited to park here.)

    • Don’t have to:


      "You don’t have to park here."


      (There’s no need to park here, but you can if you want.)


More Practical Examples for Each Case:

  • MUST:

    • "I must study for my exam tomorrow."

    • "We must leave the house by 7 AM."

  • HAVE TO:

    • "She has to take her medication every morning."

    • "They have to follow the rules at the competition."

  • MUSTN'T:

    • "You mustn’t forget to lock the door."

    • "We mustn’t eat in the library."

  • DON'T HAVE TO:

    • "You don’t have to wake up early on Sunday."

    • "They don’t have to clean the office every day."




MUST & HAVE TO & MUSTN'T & DON'T HAVE TO (MODAL VERBS)
MUST & HAVE TO & MUSTN'T & DON'T HAVE TO (MODAL VERBS)

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Very useful, thank you teacher

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