Must / Mustn't
Use it for a strong obligation, a rule, or the speaker’s certainty.
Rule
Must means strong obligation or a rule. Mustn't means forbidden, not lack of obligation. Past -> had to; future -> will have to.
Formula
| Positive (+) | Subject + must + V1 | You must finish this report.I must call her. |
|---|---|---|
| Negative (-) | Subject + mustn't + V1 | You mustn't smoke here. (forbidden!) |
| Question (?) | Must + subject + V1? | Must I do this? |
Notes
- No direct past/future forms
- Past -> had to
- Future -> will have to
- mustn't is not don't have to: forbidden is not the same as not necessary