Obligation and Necessity (Modals) 8

A. Must / Must not + infinitive without to

Must is used:

1. For strong obligation imposed by the speaker. The speaker uses must to express his/her authority.

Ex: You must be here by 8 am. (manager to employee)

2. to give strong advice.

Ex: It’s a great film. You really must go and see it.

3. to tell oneself what is necessary.

Ex: I must remember to phone Roger.

“Must not”  is used:

4. to talk about something that is not permitted.

Ex: Passengers must not smoke on the aircraft.

Ex: You mustn’t drive without your seatbelt on in Britain.

5. to give strong advice.

Ex: You mustn’t work to hard. You’ll make yourself ill.

Past form

Must does not have a past form. Had to is therefore used to refer to the past.

Ex: We had to write a formal letter in the exam.

Question form

Must is possible in question forms:

Ex: Must you wear that horrible dress?

Although “have to” is more common:

Ex: What do we have to do for homework?

B. Have to / Don’t have to:

“Have to” is used to refer to strong obligations imposed by another person rather than by the speaker or writer.

Ex: I have to be at work by 8 o’clock. The boss will get angry if I’m late. (employee toa friend)

“Don’t have to” expresses a lack of obligation.

Ex: I’m glad I don’t have to wear a suit. It’s so hot today.

C. Need to / Don’t need to / needn’t

“Need to” is used to express necessity.

Ex: Can we go to the baker’s next? I need to get some bread.

Don’t need to / needn’t express a lack of necessity.

Ex: We don’t need to / needn’t leave yet. It’s only 2 o’clock.

D. Should / shouldn’t + infinitive without to

“Should” and “shouldn’t” are used to express obligation or give advice. “Ought to” can also be used with the same meaning as should.

Ex: You ought to/should see a doctor about your backache.

Ex: If you’re on a diet you shouldn’t drink bear.

E. Be supposed to / had better:

“Be supposed to” is used to talk about what you should do because of a rule or because it is expected.

Ex: Come on, it’s 10 o’clock. You’re supposed to be in bed.

“Had better + infinitive” without “to” is used to talk about what you should do because you think it’s a good idea.

Ex: You’d better ask your dad before you borrow the car.

8 thoughts on “Obligation and Necessity (Modals)

  1. sharareh Jun 2,2010 7:06 pm

    thanks it was very good i have to be teacher in my english class next setion and i found all information here thanks a lot 🙂

  2. MEZILI HOURIA Jan 8,2011 7:06 pm

    will please help me?i want a small poem or a saying with the models (must,have to mustn’t or need.it s for teaching .thanks

  3. bouchra Mar 9,2011 11:05 pm

    :oops:thanks for help my htanks

  4. diinna Apr 10,2011 1:51 pm

    😉 thanks can help me ………

  5. cha May 14,2011 8:47 am

    😉 😐 😡 😈 🙂 😯 🙁 🙄 😛 😳 😮 :mrgreen: 😆 💡 😀 👿 😥 8) ➡ 😕 ❓ ❗

  6. Basma kazem Feb 20,2013 3:13 am

    THANX you’ve been a big help 🙂
    especially for the part about “must” appreciate it 😀

  7. Bellamy Feb 22,2013 11:00 pm

    Thank you so much! You helped a Spanish speaker so well 😀

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