Passive Voice with Modal Verbs
Learn how a modal verb combines with the passive voice, what different modal verbs add to the meaning, and how to form a modal passive about the past.
Adding meaning beyond time
A modal verb adds necessity, possibility or ability to a passive sentence.
A modal verb can be added before the passive structure, combining with be and a past participle to express necessity, possibility, ability, advice or permission.
In The task must be completed by Friday., the modal verb must adds a sense of necessity to the passive structure be completed. Compare this to The task is completed., which simply states a fact without that added meaning.
This lesson covers the pattern behind every modal passive, what different modal verbs contribute to the meaning, and how to talk about the past using this structure.
Before you begin
This is one of ten topics on the passive voice.
This lesson focuses on the passive voice with modal verbs specifically. The passive voice as a whole includes nine other topics, each covered in its own lesson.
If you would like an overview of the passive voice in general, begin with the Passive Voice page.
The central idea
A modal verb layers extra meaning onto the same passive structure.
Compare a plain passive sentence with the same sentence carrying a modal verb.
01
Plain passive
The task is completed.
02
Modal passive
The task must be completed.
The useful question is: what does the modal verb add?
Must adds necessity: the task is not yet completed, but it needs to be. The core passive structure, be completed, stays the same in both versions.
The pattern
Every modal passive follows the same structure.
modal verb + be + past participle
Whichever modal verb is used, it is followed by the base form be, never is, was, or been. The past participle then follows, exactly as it would in any other passive sentence.
What each modal adds
Different modal verbs contribute different shades of meaning.
must / have to → necessity: The form must be signed.
should / ought to → advice or expectation: The report should be finished by noon.
can → ability or general possibility: This fabric can be washed in cold water.
could / might / may → possibility: The delay could be caused by traffic.
may / can → permission: Visitors may be admitted after five o’clock.
will → a future certainty: The results will be published next week.
Talking about the past
Have been is added to place a modal passive in the past.
Present or future: modal + be + past participle
The task should be completed today.
Past: modal + have been + past participle
The task should have been completed yesterday.
This form often implies the action did not actually happen, even though it was expected to.
A useful decision guide
Ask what meaning is needed, and whether the action is past.
01
Is the sentence expressing necessity, possibility, ability or advice?
Choose the modal verb that matches that meaning.
02
Does the modal verb take the base form of be?
Every modal is followed by be, never is or was.
03
Is the action happening now, or already in the past?
A past modal passive adds have been before the past participle.
04
Does the sentence still need its past participle?
The main verb keeps its past participle form throughout.
Common mistakes
The form after a modal verb needs to stay in its base form.
Be, not is or was, follows a modal verb.
Not: The task must is completed.
Correct: The task must be completed.
Have been is needed for a past modal passive.
Not: The task should be completed yesterday.
Correct: The task should have been completed yesterday.
Without have been, the sentence does not correctly place the action in the past.
The main verb still needs its past participle form.
Not: The form must be sign.
Correct: The form must be signed.
Check your understanding
Which modal correctly completes each sentence?
Choose the correct answer for each sentence.
Which sentence correctly expresses necessity?
✅ Exactly! A modal verb is followed by the base form, be.
❎ Not quite. Check the form that follows a modal verb.
Is “be” or “is” the correct form after a modal verb?
The invoice __________ paid last week, but it wasn’t.
✅ Exactly! This describes an expectation about the past, so “should have been” is needed.
❎ Not quite. The sentence refers to “last week”, a point in the past.
Does this sentence refer to now, or to a moment already passed?
Which sentence correctly expresses general ability?
✅ Exactly! “Be” is needed between “can” and the past participle.
❎ Not quite. Every modal passive needs “be” in this position.
Is a word missing between “can” and “washed”?
Choose the best explanation
Select the sentence that explains the modal passive correctly.
Why is “The task must is completed.” not correctly formed?
✅ Exactly! Modal verbs are always followed by a base form.
❎ Not quite. Look at the word immediately after “must”.
Why does “The task should be completed yesterday.” need to be corrected?
✅ Exactly! A past modal passive needs “have been” before the past participle.
❎ Not quite. Look at the time word, “yesterday”, in this sentence.
Try it another way
Rewrite each sentence using a modal passive.
Use the modal verb given.
The report is finished by Monday. (use “must” to express necessity)
✅ Exactly! “Must be” adds necessity to the passive structure.
❎ Not quite. Add “must” before “be finished”.
The letter is sent last week. (use “should have” to express a past expectation)
✅ Exactly! “Should have been” places the expectation in the past.
❎ Not quite. Remember to add “have been” since this refers to the past.
Quick review
A modal verb adds meaning; be and the past participle stay constant.
A passive sentence follows the pattern modal verb + be + past participle.
Different modal verbs add different meanings: must/have to for necessity, should/ought to for advice, can for ability, and could/might/may for possibility.
A modal verb is always followed by the base form of be, never is or was.
A past modal passive adds have been before the past participle, often implying the action did not happen as expected.
Remember
The modal verb changes the meaning, not the passive structure itself.
Choose the modal verb for the meaning you need, then attach it to the same be plus past participle structure used in every other passive sentence.