• To get a cheap ticket, you must / have (got) to book in advance.
• Every animal on the island must / has (got) to be destroyed.
When we want to say that it will be necessary for someone to do something in the future, we use must, have (got) to, or will have to: [Quando nós queremos dizer que será necessário para alguém fazer algo no futuro, nós usamos “must”, “have (got) to”, ou “will have to:”]
• To get there on time , I must / have (got) to / will have to leave home by 8.30.
Have got to is less formal than the others, and is particularly common in spoken English. We can often use need (to) with a similar meaning: [“Have got to” é menos formal do que os outros, e é particularmente comum no inglês falado. Nós podemos muitas vezes usar “need (to) com um significado similar:”]
• Before you buy a house, you need to / must / have (got) to consider all the costs . (For mustn’t an d haven’t go t to / don’t have to)
Use have (got) to suggests that someone else or some outside circumstances or authority makes something necessary. We use must when the speaker decides it is necessary. Compare: [Use “have (got) to” para indicar que alguém mais ou alguma circunstância externa ou autoridade o torna necessário. Nós usamos “must” quando o orador decide que é necessário. Compare:]
• I have to see the head teacher, (...she has called me to her office)
• I must see the head teacher. (...I want to discuss something with her)
We prefer have (got) to when we talk about a necessity that is characteristic of a person: [Nós preferimos “have (got) to quando falamos sobre a necessidade de que é característica de uma pessoa”]
• Ann has got to have at least eight hours’ sleep a night.
• She has to drink two cups of coffee in the morning before she feels really awake.
We normally use must, not have (got) to, when we CONCLUDE that something (has) happened or that something is true: [Nós normalmente usamos “must”, não “have (got) to”, quando nós CONCLUÍMOS que algo (tem) acontecido ou que esse algo é verdade:]
• With that pile of papers on his desk, Tony must be wishing he’d never taken the job.
• The hall’s packed. There must be about 2,000 people at the meeting.
However, in informal speech, we can use have (got) to: [No entanto, em conversas informais, nós usamos “have (got) to”:]
• Look at all those penguins. There’s got to be about a million of them!
• You want to borrow more money from me? You’ve got to be joking!
When we give a negative conclusion we rarely use either must not or hasn’t / haven’t got to. Instead, we use can’t (cannot ) or couldn’t: [Quando nós damos uma conclusão negativa, nós raramente usamos quer “must not” ou “hasn’t / haven’t got to.” Ao invés disso, nós usamos “can’t (cannot)” ou “couldn’t”:]
• ‘I’m seeing Dr Evans next week.’ ‘That can’t be right. He’s on holiday then.’
• He wasn't there at the time. It couldn't have been his fault.
Must has no other forms than the present tense (no past tense, no participles, etc.) and in past tense sentences which say that it was necessary to do something, we use had to instead: [“Must” não tem nenhuma outra forma do que o presente (sem passado, particípio, etc) e em sentenças no passado que diz que é necessário fazer algo, nós usamos “had to” no seu lugar]
• Bill’s not here. He had to leave early.
• The car broke down and we had to get a taxi.
To draw a conclusion about something in the past, we use must + have + past participle: [Tirar uma conclusão sobre algo no passado, nós usamos “must + have + particípio no passado:”]
• You must have been upset when you heard the news .
• She must have played really well to win. I wish I’d seen the match .
Sometimes we can use either have to or have got to. However, we prefer have to with frequency adverbs such as always, never, normally, rarely, sometimes, etc: [Ás vezes, nós usamos tanto “have to ou have got to”. No entanto, nós preferimos “have to” com advérbios de freqüência, tais como “always, never, normally, rarely, sometimes,” etc:]
• I often have to work at the weekend to get everything done. With the past simple, we use had to, especially in questions and negative sentences:
• When did you have to give the books back? (not When had you got to...)
• We didn't have to wait too long for an answer, (not We hadn't got to...)
After contracted forms of have, has or had (e.g. I’ve, He’s, It’d) we use got: [Outras formas de “have, has ou had” (e.i I’ve, He’s, It’d) nós usamos “got”:]
• It’s got to work this time, (not It’s to work...)
In formal English we prefer have to rather than have got to. [No inglês formal, nós preferimos “have to” ao invés de “have got to”.]
Fonte: Cambridge Advanced Grammar in Use