Layered modal meanings

A modal phrase can express more than possibility or obligation. Add perfect, progressive or passive meaning and it can also tell us whether an event is earlier, ongoing or directed at its subject. The order is predictable, even when the finished chain feels dense.

Read the layers from left to right

A modal is followed by the base form of a verb. If the meaning needs more detail, add the layers in this order:

modal + perfect have + progressive be + passive be + main verb

Examples:

• The figures may have changed. Possibility + an earlier event.
• The figures may be changing. Possibility + an event in progress.
• The figures may have been changed. Possibility + an earlier passive event.
• The figures may have been being changed. Possibility + an earlier passive process in progress.

The last sentence is structurally possible but difficult to read. If the ongoing process is not essential, say may have been changed. If the agent matters, an active form may be clearer: The team may have been changing the figures.

Separate the layers of meaning

Compare should complete, should have completed and should have been completed:

The panel should complete the review today.
The panel should have completed the review yesterday.
The review should have been completed yesterday.

The first expresses a recommendation or expectation about a present/future action. The second says the panel was expected to finish earlier, often with the implication that it did not. The third keeps the same time relation but makes the review the subject.

Modal meanings depend on context. The lights must be on can express deduction; You must turn on the lights expresses obligation. Form alone is not enough: ask whether the modal concerns the truth of a claim or a required action.

Perfect modals and past evidence

Use modal + have + past participle to assess an earlier event:

The discrepancy might have resulted from a transcription error.
The warning should have been circulated before the vote.
The file cannot have been altered after the system was sealed.

The modal gives the speaker’s stance; have + participle places the event before the current point of judgement. Do not use the past form of the main verb after have.

Common mistakes

• The request may been overlooked. Use may have been overlooked.
• The report should being revised. Use should be revised for an action now/future, or should have been revised for an earlier one.
• The claim must has been exaggerated. Use the base form have after a modal.
• A chain such as may have been being monitored is not automatically wrong, but may be needlessly cumbersome.

Quick check

Choose the form that matches the meaning.

1. We are unsure whether someone changed the date earlier: The date ______ changed.
2. A rule requires someone to review the form now: The form ______ reviewed.
3. The review was expected yesterday, but it did not happen: The form ______ reviewed yesterday.

Answers: may have been; must be / should be, depending on force; should have been. State the time and attitude first, then build the verb phrase.

Separate the speaker’s stance from the event

A modal tells us how the speaker views a proposition or action; the rest of the verb phrase tells us about the event. First decide what the modal means, then add the event layers.

Two broad kinds of modal meaning

Epistemic meaning assesses how likely a proposition is:

The files must be complete.
The files may have been altered.

The speaker draws a conclusion or allows for a possibility. Deontic meaning concerns permission, obligation or what someone should do:

The files must be submitted by noon.
The files may be removed after the review.

The same modal can have either meaning. Context and the kind of subject help you distinguish them. In The door must be locked, must may express a deduction (“I conclude that it is locked”) or an instruction (“It is necessary to lock it”). If the difference matters, make the context explicit.

Perfect modals look back from a reference point

Modal + have + past participle evaluates an earlier event:

The witness may have misread the date.
The figures cannot have been checked independently.
The team should have reported the limitation.

The forms share a perfect infinitive, but their meanings differ. May have misread leaves an earlier event possible. Cannot have been checked rejects it as impossible or inconsistent with evidence. Should have reported can express criticism or an unmet expectation. A modal does not have one fixed meaning just because have follows it.

Compare these easily confused statements:

We didn’t need to repeat the test.
We needn’t have repeated the test.

The first says repeating was unnecessary; it does not say whether the team repeated it. The second normally suggests that they did repeat it, but it was unnecessary. The perfect form matters to the implied story.

Add aspect and voice only when they contribute

• may be changing: possible process in progress now.
• may have changed: possible earlier change.
• may have been changed: possible earlier passive change.
• may have been being changed: possible ongoing passive process at an earlier point.

The final version stacks possibility, past reference, progressive aspect and passive voice. It may be grammatically possible but can be difficult to process. Ask whether the reader needs all four ideas. If the agent is known, an active clause may be clearer; if progress is not important, omit the progressive layer.

Guided practice

Interpret the bold modal phrase.

1. The lock must have been changed after the inspection.
2. Staff must change the lock before the building reopens.
3. The team needn’t have repeated the measurement.
4. The figures may be changing while the software is updated.

Answers and reasoning

1. A deduction about an earlier passive event.
2. An obligation; staff are required to perform the action.
3. The measurement was repeated, but it was unnecessary.
4. A possibility about a process in progress now.

Track where the modal belongs in the chain

English modal verb phrases keep a consistent order. The modal comes first, followed by a base form; perfect, progressive and passive layers are built underneath it:

A modal never takes an -s ending or a following to in these core patterns: may have, not mays have; must be, not must to be. When a sentence contains two modals in meaning, express one through another phrase: may have to be reviewed, might be able to respond. The first modal is followed by an infinitive construction, not another core modal directly.

Negation also needs interpretation. The panel must not publish the names normally expresses a prohibition; The panel cannot have published the names expresses the speaker’s conclusion that publication was impossible. The position and meaning of not distinguish obligation from deduction. If either reading could confuse a reader, use an explicit phrase such as is prohibited from publishing or it is impossible that it published.

Further reading

• Cambridge Dictionary: modality, meanings and uses
• Cambridge Dictionary: modality and tense