English Grammar for proficiency: Modal verbs 'must'.

Must is generally used to talk about a necessity, obligation, or strong probability.

Structure
Affirmative (subject + must + V1)
• You must go now.
Negative (subject + must + not + V1)
• You must not go now.   • You mustn't go now.
Question (must + subject + V1)
• Must I go now?

Usage

Necessity
It is used to indicate that something is necessary or very important.

• I must finish my homework.

• It’s getting dark. I really must go.

• These flowers must be watered regularly.

Obligation
It is used to indicate that something is legally or formally required.

• You must not park your car here.

• You must be at least 18 years old to vote.

Strong probability
It is used to indicate that something is likely or most likely true.

• He must be upset about the news.

• He must be tired after working all day.

• She must have arrived home by now.

Recommendation
It is used to recommend something that is considered good or beneficial.

• You must read this book.

• You must save money for the future.

Emphasis
It is used with certain verbs such as 'say, admit, warn, etc.' to emphasize something.

• I must say, I am quite pleased with the results.

• I must admit, I didn't expect to win the competition.

Example Sentences with 'Must'

• I must go now.

• You must be joking.

• He must be at least 50.

• There must be some mistake.

• You must stop at the red light.

• You must not leave the party early.

• We must finish the report by Monday.

• You must take your medicine every day.

• We must leave early to catch the train.

• They must follow the rules of the game.

• There must be a better solution to this problem.

• You must have misunderstood what I said.

• They must have spent a lot of money on the wedding.

• They must have forgotten to invite us to the party.

• He must not violate the terms of the contract.

• You must admit, the view was breathtaking.

• I must warn you, the exam is going to be difficult.

• He must be running late, because he's not here yet.

• They must be having a great time on their trip.

• You must be really excited for your vacation.

• We must be prepared for the worst scenario.

• You must be careful when crossing the street.

• You must have a driver’s license to operate a vehicle.

• I must have left my wallet at the store, because I can't find it anywhere.

• There must be a mistake on the bill, because it's too high.

• There must be something wrong with the car, because it's making a strange noise.