Modals and Semi-Modals

Learning objectives

By the end of this lesson, you should be able to explain the rules, recognise the target forms in context, avoid common errors and apply the patterns to new sentences.

• Understand the core terms and distinctions.
• Study examples in complete sentences, not as isolated rules.
• Complete all 15 practice items before opening the answer key.

1. Modal form

Core modals include can, could, may, might, must, shall, should, will and would. A modal is followed by the base form without to: can swim, should study. Modals do not add -s in the third person.

2. Ability, permission and requests

Can expresses present ability or informal permission. Could can describe past general ability or make a polite request. May is often used for formal permission or possibility.

3. Advice, obligation and necessity

Should usually gives advice or expectation. Must often expresses strong obligation or a strong conclusion; have to often expresses an external requirement. Must not means prohibition, while do not have to means lack of necessity.

4. Possibility and deduction

May, might and could express possibility. Must can express a strong positive deduction; can’t can express a strong negative deduction. Could have/might have + past participle can describe unrealised or uncertain past possibilities.

5. Semi-modals and past reference

Have to, need to, ought to, be able to and be allowed to have modal-like meanings but different forms. Use be able to for ability in tenses where can is unavailable; use had to for past obligation.

Guided practice

Try each item first. Then open the answer key and read the explanation for any answer you missed.

1. She can ___ very fast. (run/runs)
2. ___ I borrow your pen? (May/Am)
3. You ___ wear a helmet when riding. (should/should to)
4. You ___ smoke here; it is prohibited. (must not/don’t have to)
5. You ___ bring food; lunch is provided. (must not/don’t have to)
6. He ___ be at home; the lights are on. (must/mustn’t)
7. It ___ rain later, so take an umbrella. (might/must to)
8. Yesterday, we ___ work late. (had to/must)
9. She will ___ able to help tomorrow. (be/is)
10. Could you ___ the door, please? (close/closed)
11. You ought ___ apologise. (to/for)
12. He ___ swim when he was five. (could/can)
13. You ___ have told me earlier. (should/should to)
14. She ___ be serious—she is laughing. (can’t/must)
15. Do we ___ to book in advance? (need/should)

Revision checklist

• I can explain the main rules in my own words.
• I can recognise the correct form in a complete sentence.
• I can explain why a common incorrect form is wrong.
• I can apply the rule to a new example.

If an answer was wrong, identify the rule behind the mistake and try writing two original examples.

Continue learning

Editorial note: Some grammar conventions vary by dialect or examination syllabus. Follow the terminology and conventions specified by your course or exam board where relevant.