Must - Have to - Need to

Man carrying full shopping basket in grocery store
I have to do the shopping. Dan Dalton/Getty Images

'Must', 'have to', and 'need to' in the positive or question form are used to speak about responsibilities, obligations and important actions.

I'm having some trouble understanding this. I must ask Peter a few questions.
She has to work with clients from all over the world.
They need to study more if they want to get good grades. 

Sometimes, 'must' and 'have to' can be used to speak about responsibilities.

However, 'must' is generally used for strong personal obligations and 'have to' is used for responsibilities at work and in everyday life. 

I must do this right now!
I have to file reports every week.

'Don't have to', 'don't need to' and 'mustn't' have very different meanings. 'Don't have to' is used to express that something is not required. 'Don't need to' also expresses that a particular action is not necessary. 'Mustn't' is used to express that something is prohibited.

She doesn't have to get up early on Saturdays. 
Children mustn't be left alone in a car. 
You don't need to go shopping as I've already gone. 

Listed below are explanations, examples and uses of must / have to / need to / and  mustn't / not have to / don't need to

Have to Do - Responsibilities

Use 'have to' in the past, present and future to express responsibility or necessity. NOTE: 'have to' is conjugated as a regular verb and therefore requires an auxiliary verb in the question form or negative.

We have to get up early.
She had to work hard yesterday.
They will have to arrive early.
Does he have to go?

Must Do - Obligations

Use 'must' to express something that you or a person feels is necessary. This form is used only in the present and future.

I must finish this work before I leave.
Must you work so hard?
John must explain this if he wants his students to succeed.
It's late. I must get going!

Don't Have to Do - Not Required, but Possible

The negative form of 'have to' expresses the idea that something is not required. It is however, possible if so desired.

You don't have to arrive before 8.
They didn't have to work so hard.
We don't have to work overtime on Saturdays.
She didn't have to attend the presentation.

Mustn't Do - Prohibition

The negative form of 'must' expresses the idea that something is prohibited - this form is very different in meaning than the negative of 'have to'!

She mustn't use such horrible language.
Tom. You mustn't play with fire.
You mustn't drive more than 25 mph in this zone.
The children mustn't go into the street.

IMPORTANT: The past form of 'have to' and 'must' is 'had to'. 'Must' does not exist in the past.

Did he have to leave so early?
He had to stay overnight in Dallas.
She had to pick the children up from school.
Did they have to do the work over again?

Need to Do - Important for Someone

Use 'need to' to express that something is important for you to do. This form is usually used for something that is important one time, rather than referring to a responsibility or duty.

She needs to go to Seattle next week.
Do you need to get up early tomorrow?
I need to spend more time with my children because I've been so busy lately.
We need to focus on getting new business this month. 

Don't Need to Do - Not Necessary, but Possible

Use the negative form of 'need to' to express that something isn't necessary, but possible. At times, English speakers use 'don't need to' to express that they don't expect someone to do something. 

You don't need to come to the meeting next week. 
She doesn't need to worry about her grades. She's a great student.
I don't need to work next Monday!
Peter doesn't need to worry about money because he's independently wealthy. 

Must / Have to / Need to- Mustn't / Don't Have to / Don't Need to - Quiz

Use either 'must','have to', 'mustn't or 'not have to' for the following questions. Once you've completed the quiz, scroll down to check you answers.

  1. Jack _____(go) home early last night.
  2. Ted ________ (buy) some food at the grocery store because we're out.
  3. _____ (she/commute) to work every day?
  1. Children _____(play) with cleaning liquids.
  2. We _____(get) going it's already midnight!
  3. When _____(you/arrive) for work last week?
  4. They ______ (mow) the lawn. It's getting too long. 
  5. You _____(do) the cleaning up this morning, I will!
  6. They _____(visit) the doctor yesterday, as they were not feeling well.
  7. I _______ (get up) every morning at six o'clock, so I can make it to work on time. 

Answers

  1. had to go / needed to go
  2. needs to buy / has to buy
  3. Does she have to
  4. mustn't play
  5. must get
  6. did you have to arrive
  7. need to mow
  8. don't need to do
  9. had to visit (there is no past for 'must')
  10. have to get up