Auxiliary Verb MUST :
1. Joris must be at least 50.
2. I am sure he is at least 50.
3. No. He can't be over 45.
4. I am sure he is not over 45.
5. He must have married years ago.
6. I am sure he married years ago.
7. We can't have been at college together.
8. I am sure we weren't at college together.
9. They'll be back by now.
10. I'm sure they're back.
11. No. They won't be there yet.
12. I'm sure they are not there yet.
13. Mary will have arrived already.
14. I'm sure she's arrived already.
15. No. She won't have left home yet.
16. I am sure she hasn't left home yet.
: MUST HAVE is the past form of MUST when it is used to express certainty.
and MUST HAVE
express stronger certainty than WILL and WILL HAVE.
CAN'T and CAN'T HAVE express stronger certainty than WON'T and WON'T HAVE.
MUST : (verb) - 3rd person singular
MUSTN'T - Negative short form
HAD TO - past - usually
MUST : modal + verb
MUST : shows what it is necessary for one to do (or) what one ought to do (or) what one is forced to do
: (verb) - 3rd person singular
OUGHT - present tense
OUGHTN'T - negative short form
OUGHT - modal + to verb
OUGHT - to have the moral duty to do something (or) obligation (or) requirement
1. You must finish this job by tomorrow.
2. I must phone my son tonight.
3. He had to finish the job by the next day.
4. You don't have to do it until next week.
5. It is not necessary.
6. You don't need to do it until next week. It is not necessary.
7. You needn't do it until next week. It is not necessary.
8. You mustn't smoke in the cinema. It is forbidden.
9. I didn't need to get up early this morning.
10. The speaker did not get up early.
11. The speaker did, in fact, get up early.
12. You needn't have bought me a present.
13. But you did buy a present.
HAD TO is the best form of MUST when it is used to express obligation.
1. Don't have to…
2. Don't need to…
4. Must not…
These expressions used to show that there is an obligation not to do something.
These expressions are used to show that there is no obligation.
The contracted forms NEEDN'T and MUSTN'T are common expressions.
1. You should give up smoking.
2. You ought to give up smoking. (advice)
3. We should go to that new theatre one day.
4. We ought to go to that new theatre one day. (suggestion)
5. The members should have been consulted in the matter.
6. The members ought to have been consulted in the matter.
7. This sentence means that they were not consulted.
8. You shouldn't work so hard, you know.
9. You ought not to work so hard, you know.
: The contracted form OUGHTN'T is common usage in English.
1. The meeting should be over now.
2. The meeting ought to be over now. (I expect it is…)
3. He should be home at 5 O'clock today.
4. He ought to be home at 5 O'clock today. (I expect he will be…)
5. They should have received our letter by now.
6. They ought to have received our letter by now. (I expect they have…)
: In this meaning, SHOULD & OUGHT TO are not as strong as WILL & MUST.
Auxiliary Verb MUST
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