“Must” and “have to”

General comments

The verbs “must” and “have to” have very similar meanings. Both are used to talk about things that we have an obligation to do, or things that we are sure about. But there are certain differences between the two verbs. In particular, “must”, as a modal verb, has only one form, and it is used only in the present tense. Whenever you need to use another tense, or an infinitive form, “have to” is your only choice. So, for example, “must” is possible only in the first of these three sentences:

Present: I must / have to go home now.Infinitive: I hate to have to go home now.Past: I had to go home then.

1. Obligation and necessity: present tense

“Must” and “have (got) to”* are both used to talk about obligation and necessity:• Employees must / have (got) to wash their hands before returning to the kitchen.• I must / have (got) to remember to call her after work.

Both verbs are used in the same way in this context, although there is a slight difference between US and British usage. In US usage, “have (got) to” is used much more frequently than “must”. For details on British usage, and for talking about obligation and necessity in other tenses, see the opposite page.

2. Certainty: present tense

“Must” and “have (got) to”* are also commonly used to talk about certainty:• This must / has (got) to be the worst job in the whole company.• That must / has (got) to be the stupidest idea I’ve ever heard.

In US usage, one usually hears “have (got) to” in this context. In British English, “must” is far more common. For talking about certainty in other tenses, see the next page.

*Note that in the present tense, the affirmative forms of “have to” and “have got to” are interchangeable.

3. Negative forms

The negative forms “must not” and “do not have to” have totally different meanings.The negative form “must not” is used to forbid people to do something:

• You mustn’t tell anyone I told you! I would be in big trouble if anyone found out.• You mustn’t talk that way to a client. It’s bad for business.• I mustn’t forget to call them.

In contrast, “don’t have to” is used to express that it is not necessary for something to be done:

• Oh, you don’t have to clean up. I’ll do that.• I don’t have to stay if I don’t want to.

Note that the Spanish translation of “you don’t have to” is no tienes que/no es necesario (que lo hagas). “You must not” should be translated as no debes/deberias.

Advanced usage

Obligation and necessity: present tense (British usage)

British speakers often use “must” when talking about their own feelings about what is necessary. On the other hand, they often use “have (got) to” to talk about other people’s opinions of what has to be done:

• I must listen to her speech!Necesito escuchar su discurso!

• I’ve got to listen to her speech. Boss’s orders.Tengo que escuchar su discurso. Ordenes del jefe.

Obligation and necessity: other tenses

When talking about obligation and necessity in the past, we use the form “had to”. There is no past-tense form of “must”:

• I had to call her after work.• She had to finish up her project last night.

When talking about an obligation in the future, “will have to” is used. When talking about the near future and arrangements that have already been made, “have (got) to” is preferred:

• You’ll have to look for a new job when the boss leaves.• I’ve got to go to a job interview next week.

For orders and explicit instructions on what to do in the future, use “must”. To make the statement more indirect, use “will have to”:

• I’ll lend it to you, but you must bring it back tomorrow.• I’ll lend it to you, but you’ll have to bring it back tomorrow. 

Certainty: other tenses

To express certainty about the past, use “must have” + past participle:• She’s not there. She must have left already.• He was really red in the face. He must have been very angry.

Neither “must” nor “will have to” is used to express certainty about the future. Use the future tense with “certainly” or “definitely” instead:

• This will definitely be our last attempt.

This will certainly not be repeated.