We have prepared this lesson to help you understand how to use ‘have to’, “must’,  ‘don’t have to’ and ‘mustn’t’.

 

Here's how to use them:

 

1) Must = Obligations

We use “must” for obligations. Think of a policeman, a boss, a teacher, or a parent talking to their child. 

 

Examples:

- You must wear a seatbelt.

- I must stop spending time talking to my girlfriend and get to work, or my boss will fire me.

 

NOTE: It is impossible to conjugate “must” in the past and the future. 

- We will must arrive at work on time. - INCORRECT

- We didn’t must arrive at work on time. - INCORRECT

 

2) Have to = Responsibilities

We use “have to” for responsibilities. Think of routines, plans, or resolutions.

 

Examples:

- I really have to stop drinking so much coffee.

- Listen, you will have to wake up early tomorrow, if we’re going to have brunch downtown.

 

NOTE: As a regular verb, “have to” can be conjugated in the past and the future.

- He will have to try harder.

- I had to wait in line for three hours.

 

3) Must not = Prohibitions

We use “must not” when we are not allowed to do something. Think of illegal actions or terrible ideas.

 

Examples:

- You must not smoke in the hospital. 

- The children must not climb on the statues.

- This is a museum, not a playground.

 

4) Don’t have to = Not necessary

We use “don’t have to” when something is not required.

 

Examples: 

- I appreciate the offer, but you don’t have to wash the dishes.

- If you want to, I’m not going to stop you.

- My uncle doesn’t have to go to work on Sunday.

- He does it because he likes his job and he has no family.

 

✔ In contemporary, spoken English, we use “have to” and “must” interchangeably. It is not an error to use “must” for responsibilities or “have to” for “obligations”.

 

 Examples:

 

- You must stop at red lights.

- You have to stop at red lights.

 

- I loved Rocky 2070. You must see it.

- I loved Rocky 2070. You have to see it.

 

✔ However, there is a significant difference between “must not” and “don’t have to”. They cannot be interchanged.

 

Examples:

Correct:

- The children must not throw eggs at cars.

 (This means that throwing eggs at cars is illegal). 

 

Incorrect:

- The children don’t have to throw eggs at cars.

(This means that they can throw eggs at cars if they want, but that no one is obligating them to do so).

 

Let’s practice!

 

1.) My neighbor was arrested again. He _________________________ stop driving drunk.

a.) must b.) doesn’t have to

 

2.) My sister is very generous. She _________________________ prepare dinner for all of us, but she likes sharing meals with friends.

a.) must not b.) didn’t have to

 

3.) Those are Farmer Brown’s chickens. You _________________________ steal them.

a.) must not b.) didn’t have to

 

4.) We will _________________________ be patient, if we want to cross the city by bus.

a.) must b.) have to

 

5.) All pet owners _________________________ keep their dogs on a leash.

a.) must b.) must not

 

6.) Littering is illegal in this city. You _________________________ throw trash in the street.

a.) don’t have to b.) must no

 

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