The modal verb must is used for many expressions.
- She must smile more often. (Suggestion)
- You must bring along your own calculator. It’s not provided. (Command/Advice)
- She has been talking for so long her mouth must be very dry now. (Opinion)
- All of you must come over for the tea party next weekend. (Invitation)
- You haven’t eaten a pear for a long while, and you think you must pluck one from your neighbour’s tree? (Desire)
- You have a big pond, so you must keep some ducks. (Insistence)
Must is used to show something is required.
- You must sign the visitor book..
- All applicants must fill in all the pink forms.
- We must stop at the library to renew the books.
Must is used to show something is necessary.
- You must follow the step-by-step instructions to get it working.
- The advice is she must do 30 minutes of vigorous exercise every day to shed off the excess fat.
- You must see the doctor about that lump on your cheek.
Must is used to show something is required by a rule or law.
- All passengers must gather here fifteen minutes before departure.
- You must obey the rules and not bring your pet monkey here.
Must is used to show something that is very likely or possible.
- They must be arriving soon.
- It must be almost one hundred people in that long queue.
- He must be the skinniest member of his family.
Must is used to emphasize a statement.
- I must say that big man was a real coward. (Emphasis)
- You must admit you are wrong, and they are right..
Must is used in questions to express annoyance or anger.
- Must you visit the toilet so many times?
- Why must you always say I’m wasting my time watching television?
- Must you always be as stubborn as a mule?
We use had to, not must to express obligation and necessity in the past.
- Yes: I didn't pass my exam and had to sit it again.
No: I didn't pass my exam and must sit it again.
- Yes: Yesterday, we had to take a taxi home when the rain began to fall.
No: Yesterday, we must take a taxi home when the rain began to fall.
Must is used for a future action in the past.
- It was still a long way to go, but we knew we must arrive in the city before it got dark.
- The police had no leads in the case, but they must carry on investigating into the woman’s murder.