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2. Match the phrases, a) – g), taken from the text, to the descriptions, I) – IV).

a) you are not allowed to bring any food i) a present obligation

b) you can chew a gum ii) necessity

c) you must not smoke iii) permission

d) you are not permitted to take photographs iv) prohibition

e) you need to obtain permissions

f) someone has to clean up all fingerprints

g) you are allowed to use your iPod

Language Reference

Obligation: This is a requirement to do something which comes from the speaker.

Necessity: This is a requirement to do something which comes from external circumstances (for example, rules and customs) or the situation.

Obligation

The verbs must, have to and have got to can all be used to express obligation:

You must tell me. You promised. / You have to tell me. You promised.

Note, however:

  • must is more common than have to in conversation to express obligation.

  • have got to is used especially in spoken English: I've got to go now.

  • to express past or future obligation, we use have to.

Necessity

The verbs must, have to / have got to and need to can all be used to express necessity. Note, however:

  • when the necessity is due to a rule, have to or need to is usually used:

You have to wear a uniform in the army. I need to / have to be at work by 8.45 every day.

  • Must is often used in public notices or signs:

Visitors must report to reception. Guests must be signed in at the desk.

Negatives

We use mustn't to express an obligation or necessity not to do something:

You mustn't talk about people behind their backs. (this is a bad thing to do)

Bananas mustn't be kept in the fridge. (this is not a good thing to do)

  • We use don't have to / haven't got to when obligation / necessity is usually expected, but not on this occasion or in this situation:

I don't have to go to school today. It's a holiday. (I usually go to school, but today is a holiday)

We don't have to wear a uniform at my school. (I can wear my own clothes)

  • Don't need to is similar to don't have to to express freedom from necessity:

You don't need to bring a sleeping bag. We've got a spare duvet.

Need not is also possible:

You needn't worry.

Questions

  • Questions with have to and have got to are common:

Do I have to go to school today? Have I got to wear smart clothes?

  • Questions with must / mustn't are unusual, but possible:

Must I go to school today?

Other points

  • Words like just, only, also, always, sometimes etc. come before have to / have got to / need to but after must:

You only have to do it once. You must only do it once.

  • The present perfect form is:

We've had to sell the boat. The restaurant's had to close.

  • Other verbs can express obligation or necessity:

I insist that you leave now. (obligation) You are required to leave now. (necessity)

Practice

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