How to use “Must” and “ Have to”
Unit 3
Must vs. Have to
Must
Necessity, strong obligation
Ex: I must write a letter to Bob.
(I decided to write a letter. Nobody else told me to write it. I think it is necessary.
Have to
Obligation, Rules, laws, other wishes
Ex: I have to write a letter to John.
(I didn’t decide to write a letter. Someone else told me to write it)
Must vs. Have to
Must
Necessity, strong obligation
Ex: I must book a hotel for my trip next week.
(I am reminding myself that it is necessary to do. I have decided it is necessary)
Have to
Obligation,Rules, laws, other wishes
Ex:I have to wear a uniform at work.
(My boss makes us wear a uniform. It is an obligationthat our boss has decided.)
Teacher: You must complete the essay by Friday.
(The teacher is giving the students an obligation)
Student: We have to complete the essay by Friday.
(The teacher has given us the obligation)
Must can use only in the present tense.
Have to can be used in other tenses.
The past form: had to
I had to pay my speeding ticket yesterday.
Examples
I have to leave early today.
He has to see the doctor.
You have to drive slower than 110 km/h on highways.
You have to wear uniform in class.
I have to finished this report by 5:00.
You must work hard.
All passengers must wear seat belts.
We must fasten our seatbelts.
You must stop palying computer games.
She must stop playing computer games.
Banks must examine all documents.
You must be on time.
You must call her.
Official, written rule
You must be 18 or older to vot in the U.S.
Necessaity
I have to wear glasses to see.
Strong recommendation/ advice

You must visit DC when you are in The U.S.
Bob is a good person. You must meet him.
You must read this book. It’s amazing.
If you go to Paris, you must take a walk by the river at night.
We must hire some new staff as soon as possible.
Must: a logical conclusion (deduction)

They must be rich. Their house is huge.
It must be a difficult exam; only 10 % of candidates pass.
It must have rained last night.
He is eating a lot of pizza. He must like pizza.
This must be her house. I can see her car in the garage.
Mustn’t: Prohibition
something is not allowed/ forbidden
Ex: You mustn’t smoke here.
Mobile phones must not be used while the plane is flying.
Children mustn’t talk to strangers.
Cars mustn’t park in front of the entrance.
Don’t have to: no obligation
You are not required to do something, especially if you don’t want to.
Ex: You don’t have to make excuses for her.
You don’t have to whisper, no one can hear us.
Negative of must
You must not drink that.
(It is forbidden to drink that.)
You mustn’t tell John.
(Do not tell John.)
(You are not allowed to tell John.)
Negative of have to
You don’t have to drink that.
(You don’t need to drink that but you can if you want.)
You don’t have to tell John.
( you can tell John if you want to but it is not necessary. You decide if you want to.)
You musn’t get on the the bus without a ticket.
You musn’t drive through a red light.
You musn’t touh the ball with your hands when you play football.
You mustn’t use your mobile phone in class.
You mustn’t stand-up in a small boat.
You mustn’t arrive late for you’re appointment.
You mustn’t touch the animals at the zoo.
She mustn’t come.
(It is important that she does NOT come. Maybe because we are organizing a surprise for her and we don’t want her to know about it.)
She doesn’t have to come.
(Here we let her now about the meeting or whatever. She is not required to come but she can if she wants to.)
Goodbye!