“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.