Must vs. Have To
Must and have to can both express obligation, but their typical sources and negative forms differ. Must often presents an obligation from the speaker or rule; have to commonly points to external necessity, while mustn’t means prohibition and don’t have to means lack of necessity.
Both can express obligation, but mustn’t means “not allowed,” whereas don’t have to means “not necessary”; choose with the source, tense, and strength of obligation in mind.
Key details
Choose the right form
| Choice | Use it when | Example |
|---|---|---|
| must | strong/speaker-presented obligation | I must call her. |
| have to | external or circumstantial necessity | We have to wear badges. |
| mustn’t | prohibition | You mustn’t enter. |
| don't have to | lack of necessity | You don't have to come. |
Further guidance
Meaning Boundary
Must also has deduction uses; this guide’s core comparison is obligation and necessity.
Tense Boundary
Past obligation is normally expressed with had to rather than a past form of must.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- Must (opens in a new tab)Cambridge Dictionary · Must and have to for obligation, including the must not versus do not have to distinction