When a modal verb appears in a passive sentence, it keeps its usual position at the front and is followed by the infinitive be plus the past participle.
The modal itself does not change. Only the verb after it shifts from active to passive: finish → be finished, send → be sent, take → be taken.
Active to passive
The structure mirrors the regular passive shift. The active object becomes the subject, the doer is usually dropped, and the main verb moves to its past participle form.
The meaning of the modal — obligation, possibility, ability, future — carries over unchanged. Must be finished still expresses necessity; can be solved still expresses ability.
Form with the main modals
| MODAL | PASSIVE EXAMPLE |
|---|---|
| can | The problem can be solved quickly. |
| could | The door could be opened from outside. |
| may | Photos may be taken during the tour. |
| might | The meeting might be cancelled. |
| must | Passports must be shown at the gate. |
| should | Old files should be deleted. |
| will | The results will be announced on Monday. |
| would | The work would be finished by noon if we started now. |
Have to behaves like a modal in meaning but conjugates as a normal verb, so both have to and has to are possible.
Negatives and questions follow the same pattern as other modals: cannot be solved, should not be deleted, Must this be signed today?, Can the date be changed?
Modal perfect passive
To talk about a past action, the modal is followed by have been + past participle.
The perfect part (have been) stays the same for every modal; only the participle at the end changes with the main verb.
| MODAL | PASSIVE EXAMPLE |
|---|---|
| should | The client should have been told earlier. |
| must | The keys must have been stolen during the break. |
| could | The accident could have been prevented. |
| might | The letter might have been lost in the post. |
| may | The data may have been copied before the system crashed. |
| would | The project would have been finished on time with more staff. |
The same meanings carry over from the active modal perfect. Must have been stolen expresses a confident past deduction; should have been told expresses a past obligation that wasn't met; could have been prevented expresses past possibility that didn't happen.
Common mistakes
Missing "be" after the modal
Wrong verb form after "be"
Conjugating the modal
Modal perfect passive — wrong auxiliary
Adding a second "to"