Modal auxiliary verbs (II) : Must – Should – Ought to

Must: obrigaçăo, necessidade no presente ou futuro

        She must leave early tomorrow. ( *Not must to leave * *musts to leave* *musts leave*)

(NO to-infinitive or third person –(e)s ending)

         Must you leave now? (NOT *Do you must...)

      


Must is personal. We use must when we give our personal feelings.

‘You must do something’= ‘I (the speaker) say it is necessary’:

She’s really nice person. You must meet her. (= I say this is necessary)

I haven’t phoned Ann for ages. I must phone her tonight.

Compare:

I must get up early tomorrow. There are a lot of things I want to do.

 

Have to is IMPERSONAL. We use have to for facts, not for our personal feelings.

‘You have to do something’ because of a rule or the situation:

You can’t turn right here. You have to turn left. (because of the traffic system)

My eyesight isn’t very good. I have to wear glasses for reading.

George can’t come out with us this evening. He has to work.

I have to get up early tomorrow. I’m going away and my train leaves at 7:30.

Must: DEDUCTION

    She’s been studying all afternoon. She MUST have a test tomorrow.

        She’s not here, she MUST be at home.

Must and Can’t: refer to present time only. In expressing certainty, they are opposites:

        This must be our stop. (I’m sure it is.)

        This can’t  be our stop. (I’m sure it isn’t)    

Must * had to

        Our son was very ill last night and we had to call the doctor.  (Not * must call * musted call *  * musted to call* )

        (Must has no past form and we use had to to express

 ‘inescapable obligation’ in the past)

        My lawyer said he must/had to warn me not to answer any questions.

        (we can use must or  had to as past forms in indirect speech)

MUST HAVE + PAST PARTICIPLE: Deduction in the past

        Someone MUST HAVE TAKEN it. (I’m sure they did.)

        Surely you MUST HAVE NOTICED it!

        The phone rang but I didn’t hear it. I MUST HAVE BEEN asleep.

        I’ve lost one of my gloves. I MUST HAVE DROPPED it somewhere.

        ‘You must do something’=it is necessary that you do it.

        ‘You mustn’t do something’=it is necessary that you do not do it (so don’t do it) (prohibition)

        ‘You needn’t do something’=it is not necessary that you do it, you don’t need to do it.

Should/ ought to: dar conselhos, lembrar

        I’m sure your mother’s worried. You should phone/ ought to phone her.

        (should and ought to when we give advice)

        We must leave by 3 to avoid the rush hour.

        (MUST for ‘ inescapable obligation’)

Should HAVE + PAST PARTICIPLE / Ought to HAVE + PAST PARTICIPLE  Usado para indicar algo que deveria ter acontecido no passado, mas năo aconteceu.

        I didn’t know you’d been so sick. You should have told/ ought to have told me.

        (i.e. it was your duty to do this, but you didn’t do it)

 

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