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.