Modal Verbs & Modality

What are modal verbs?

Common modal verbs include can, could, may, might, must, shall, should and would.

They are followed by the base form of the main verb:

• She can swim.
• They might arrive later.
• You should revise the introduction.
• We must leave now.

Possibility and certainty

Modal verbs can express different degrees of certainty.

Compare:

• It might rain later. → possible
• It may rain later. → possible
• It must be raining. → the speaker sees strong evidence
• It cannot be true. → the speaker believes it is impossible

Obligation and advice

Must and have to often express strong obligation, while should usually expresses advice or a weaker expectation.

You must submit the form today.

I have to leave before six.

You should check your sources before submitting the essay.

Permission and ability

Can and may can be used for permission in different contexts.

Can also commonly expresses ability.

• Can I borrow your notes?
• May I come in?
• She can speak three languages.

Past meaning

Modal meaning can also refer to the past.

Could can express past ability in some contexts.

Modal + have + past participle can express judgments about past events:

• They might have missed the train.
• You should have checked the deadline.
• She must have misunderstood the instructions.

Modality in academic language

Modality is important in formal and academic writing because claims often need to be qualified.

Compare:

• The policy causes lower emissions.
• The policy may contribute to lower emissions.
• The results suggest that the policy could reduce emissions under certain conditions.

Sentence A: This proves that social media harms all teenagers.

Sentence B: This may suggest that some forms of social media use can have negative effects on some teenagers.

Sentence B uses modality to match the strength of the claim to the evidence more carefully.

1. Decide what meaning you want: ability, possibility, obligation, advice, permission or certainty.
2. Choose a modal that matches the strength of that meaning.
3. Use the base form after the modal.
4. For past judgments, consider modal + have + past participle.
5. In formal writing, check whether your claim is stronger than the evidence allows.

Incorrect: She can speaks English.

Correct: She can speak English.

Incorrect: They must to leave.

Correct: They must leave.

Too strong: The results prove that the method always works.

More careful: The results suggest that the method may be effective in some contexts.

Which sentence best expresses a cautious conclusion based on limited evidence?

• A. The programme definitely improves every student's results.
• B. The programme may improve results for some students.
• C. The programme must improve every result.
• D. The programme cannot have any limitations.

Answer: B. May expresses possibility without claiming more certainty than the evidence supports.

• Modal verbs express meanings such as possibility, obligation, advice and certainty.
• A modal is normally followed by the base form of the verb.
• Different modals express different degrees of strength.
• Modal + have + past participle can express judgments about past events.
• Modality helps writers make appropriately cautious and precise claims.