Small words, big meaning: A modal verb is a helper verb that sits in front of a main verb and adds a layer of meaning — ability, permission, possibility, obligation or advice. The core modals are can, could, may, might, must, shall, should, will, would, plus the semi-modals have to and ought to.
"I swim" is just a fact. "I can swim", "I must swim", "I should swim" each say something different about that same action — and that nuance is exactly what examiners reward.
- modal verb
- a helper verb (can, must, should…) that changes the meaning of the main verb
- main verb
- the verb that carries the action (swim, go, study); it follows the modal
- bare infinitive
- the base form of a verb with no 'to' (swim, go, study)
- ability
- being able to do something — expressed with can / could
- permission
- being allowed to do something — expressed with can / may
- possibility
- something that may or may not be true — expressed with may / might / could
- obligation
- something you are required to do — expressed with must / have to
- advice
- what is a good idea to do — expressed with should / ought to
Why it carries the marks: Modals appear in every skill — a notice that says what you must do, a text discussing what people should change, an opinion about what we could improve. Using a range of modals accurately is core Criterion A (Language), and they are the natural way to give advice and opinions in writing and speaking.
Three rules that cover every modal: Modals are wonderfully simple because they break the normal verb rules in the same way every time:
1. + bare infinitive — the verb after a modal has no 'to': "She can swim" (not "to swim"), "You should go".
2. No -s on he/she/it — modals never change: "He can", "She must", "It might" — never "cans", "musts".
3. Questions and negatives need no 'do' — invert for questions ("Can you help?") and just add not for negatives ("You must not run", "She cannot come").
| Modal | Main use | Example |
|---|---|---|
| can / can't | ability, permission | I can drive. / You can't park here. |
| could | past ability, polite request | I could read at four. / Could you help me? |
| may | permission, possibility | You may leave. / It may rain later. |
| might | possibility (less certain) | She might be late. |
| must / mustn't | strong obligation, prohibition | You must wear a helmet. / You mustn't smoke here. |
| should / shouldn't | advice | You should rest. / You shouldn't worry. |
| will / won't | future, promise, willingness | I will call you. / He won't listen. |
| would | polite request, hypothetical | Would you like tea? / I would travel more. |
| have to | obligation (often external) | I have to wear a uniform at school. |
must vs have to in the negative: In the positive, must and have to are close (both = obligation). In the negative they split: mustn't = it is forbidden ("You mustn't be late" = don't be late), while don't have to = it is not necessary ("You don't have to come" = you can if you want, but you needn't). Don't mix them up.
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Match the modal to the meaning: Choosing the right modal is mostly about meaning. Ask yourself: am I talking about what someone is able to do, allowed to do, what might be true, what they must do, or what they should do? Each meaning has its go-to modal.
The five meanings and their modals
- Ability — can / could: "I can ride a bike", "She could already read at four."
- Permission — can / may: "You can borrow it", "May I come in?" (may is more formal).
- Possibility — may / might / could: "It might snow", "That could be true."
- Obligation — must / have to: "Drivers must stop at a red light", "I have to work on Saturday."
- Advice — should / ought to: "You should drink more water", "We ought to leave early."
Stronger / more certain
- must — a strong obligation or near-certainty
- will — a confident prediction or promise
- can — a clear, present ability or permission
Softer / less certain
- should — advice, not a command
- might / may — a real but uncertain possibility
- could / would — tentative, polite, or hypothetical
Modals are perfect for opinions: When the task asks you to give a view or persuade, modals do the heavy lifting: "Governments should invest more in transport", "Young people could make a real difference", "We must act now." A confident modal turns a flat statement into an argument.
A short text built on modals: Here is a short, everyday paragraph built one sentence at a time. Each sentence uses a modal verb to express a different meaning — ability, obligation, advice, permission and possibility. Read it once for meaning, then notice which modal does which job.
IB-style task — modals in action
One paragraph, sentence by sentence
- Ability (past → present): "When I was younger, I couldn't swim at all, but now I can swim quite well." — couldn't / can compare ability then and now.
- Obligation: "If you want to enter the pool area, you must wear a swimming cap — it is a strict rule." — must signals a strict rule.
- Advice + possibility: "You should warm up before you get in; otherwise you might pull a muscle." — should gives advice; might warns of a possible result.
- Permission + ability: "Beginners may use the shallow end, and they can ask a lifeguard for help at any time." — may and can grant permission and state ability.
- Ability + obligation: "Honestly, anyone can learn to swim — you just have to practise a little every week." — can (ability) and have to (necessity) round off the advice.
Steal this for your own writing: Notice how few patterns you need: pick the meaning, choose the modal, then add a bare infinitive. Swap in your own topic — phones, the environment, school — and you have ready-made, mark-scoring sentences for the oral or a writing task.
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The slips to watch for: Three mistakes dominate at SL: adding 'to' after the modal ("should to go" instead of should go), adding -s in the third person ("she cans" instead of she can), and using 'do' to make a question or negative ("Do you can…?" instead of Can you…?). Compare the right version with the typical mistake and the fix becomes obvious.
Correct
- You should rest before the exam.
- She can speak three languages.
- Can you help me, please?
- You don't have to come if you're tired.
Common mistake
- You should to rest before the exam. (extra 'to' — drop it)
- She cans speak three languages. (no -s on a modal — 'can')
- Do you can help me, please? (no 'do' — just 'Can you…?')
- You mustn't come if you're tired. (wrong meaning — that forbids it)
Two quick checks before you write a modal: 1. Is the next verb a bare infinitive (no 'to', no -s, no -ing)? "She must leave", not "to leave" / "leaves". 2. For a question invert (Modal + subject + verb: "Should I go?"); for a negative add not to the modal ("You should not worry"). Never bring in 'do'.