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Modal verbs — can, should, must
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Modal verbs — little helpers
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Modal verbs can express ability, permission, advice or a rule. Read the situation as well as the verb.
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Core modals here: can, could, should, must. The related obligation pattern have to works differently: She has to go. Does she have to go?
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After these core modals, use a base verb: She can swim. You must go. Keep to in the separate have to pattern. Outcome: distinguish ability, advice, a requirement and no requirement. Start with can; does You don't have to come forbid coming? No — it says coming is not required.
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Allow about 45–60 minutes across sessions, including later review. This is a study suggestion, not test timing or a proficiency estimate.
I can swim, but I must wear a cap: being able to swim is not the same as a requirement.
can / could — ability & requests
- Can can describe ability: I can swim. In a rule context it can give permission: You can bring water into this room. Being allowed to do something does not establish physical ability.
- could = past ability, or a polite request: She could read at four. Could you help me?
- After can / could, use the base verb: can swim (not can to swim).
Which sentence is correct?
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Can takes base swim in this frame: I can swim. The no-to pattern here applies to the core modal can, not to have to swim or ought to swim.
Mina is able to cook. Which sentence states that ability with a base verb?
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Can cook uses the base verb. Can to cook and can cooking do not fit this core-modal frame. The pattern is not the have-to frame, which keeps to.
should — advice
- should = advice, "it's a good idea": You should see a doctor.
- Negative shouldn't = "it's not a good idea": You shouldn't eat so late.
- Advice often leaves more choice than a requirement, but the words alone do not guarantee a gentle tone. Should can also express an expectation: The bus should arrive soon. Read the whole context.
Give advice using the one-word modal meaning ought to: You ___ see a doctor.
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Should supplies the specifically requested one-word advice modal. You could see a doctor can also be natural advice or a suggestion in another task; it is not the requested ought-to meaning here.
Translate into English: 你应该去看医生。
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You should see a doctor is the model advice. You ought to see a doctor is another natural translation; a grammatical to in that frame is not the same as the incorrect should to see.
A friend studies until midnight and looks exhausted. Choose the advice.
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Shouldn't study gives advice with a base verb. Must to study adds to after a core modal, and don't have to studying uses an -ing form in the have-to frame.
must / have to — obligation
- In these obligation contexts, must and have to express necessity: You must wear a seatbelt. I have to get up early. Have to changes form: has to, had to; its ordinary questions use do/does/did.
- mustn't = it's forbidden: You mustn't smoke here.
- don't have to = it's not necessary: You don't have to come.
What does the modal do?
Classify the intended ability, advice and obligation readings in these examples. Other contexts give can/could/should/must other meanings; have to has its own has to/had to forms.
On a no-smoking notice, “You mustn’t smoke here” states a rule. Does it mean smoking is forbidden?
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Yes, in this explicit rule context mustn’t forbids smoking. Don’t have to would instead remove a requirement; it would not express this prohibition. Interpret the whole context rather than assigning every modal one compulsory meaning.
Choose the core-modal frame: You must ___ now.
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Must go takes the base verb. Must to go is the mistake named for this core modal. Going is not the base form. Have to go is a different pattern and is not the frame asked for here.
One person has a necessary finish today. Choose the have-to frame: She ___ finish today.
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She has to finish uses the third-person form of have to and keeps to. Musts adds an ending the core modal does not take, and have to does not agree with she.
Common mistakes
- For the core-modal pattern here, use You must go, not You must to go. This does not remove to from have to go or the different pattern ought to go.
- The core modal stays must: She must study, not musts. Contrast the separate pattern She has to study; do not apply one form rule to both.
- In these rules, mustn't means not allowed; don't have to means not required. These are different meanings, not interchangeable negatives. A lack of requirement does not itself tell you every other rule that may apply.
Match the intended rule, no-requirement and advice meanings of these example sentences.
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In these contexts, mustn’t park forbids parking; don’t have to come removes a requirement; should rest advises; must wear a seatbelt states a requirement. Lack of a requirement is not itself a full statement of every permission or rule, and these are not all possible modal meanings.
Express a past obligation using have to: Yesterday I ___ work late.
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Had to is the past form of have to for this past requirement. It is not an invented inflected form of must. This practice frame does not mean must can never occur in a past report.
The club says joining is optional. It does not forbid joining. Which sentence matches?
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Don't have to join removes a requirement. Mustn't join would forbid joining, and must to join both states a requirement and adds to after must.
- The core modals practised here take a base verb; have to has its own to and changes to has to / had to.
- Context can give can/could an ability, permission or request meaning. Should can advise or express an expectation; no single label covers every use.
- In these rule contexts, must / have to = required; mustn't = forbidden; don't have to = not required.
A friend is tired and stressed. Write one sentence of advice using “should”.
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Example: “You should go to bed early and relax.”
Three worked contrasts
- Ability and permission: Rae can swim can describe a skill. A pool notice saying You can swim here gives permission in that context; it does not test anyone’s skill. Near miss: The notice proves every visitor is able to swim adds a fact. Keep the permitted activity separate from the person’s ability.
- Forbidden and not required: A study-room rule bans running: You mustn’t run here. Wearing a coat is allowed but optional: You don’t have to wear a coat. Near miss: You mustn’t wear a coat changes no requirement into a ban. Restore the stated option; no requirement alone is not a complete account of other rules.
- Core modal and have to: She must leave keeps must unchanged. She has to leave / Does she have to leave? uses has in the statement and base have after does. Do I have to leave? asks about the speaker. Near miss: Does she must to leave? mixes frames. Repair the chosen frame without claiming that must and have to always express exclusive kinds of necessity.
Independent decisions
- Use only the fact in the question. A base verb after can, could, should or must is a different pattern from have to.
- After a miss, name the error: the verb form, or the meaning (ability, advice, a requirement, a prohibition, or no requirement).
Choose the polite request that keeps a base verb after could.
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Could you open uses the base verb in a request. Could you to open and could you opening do not fit the core-modal frame.
At age four she was able to read. Which sentence fits that past ability?
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Could read states the past ability with a base verb. Could to read adds to, and musts read is neither the past-ability form nor a grammatical core modal.
Someone has a sore throat. Choose advice, not a broken requirement frame.
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Should see is advice with a base verb. Must to see and should to see put to after a core modal.
The speaker expects the bus soon and is not stating a law. Which sentence fits?
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Should arrive can express this expectation, with a base verb. Should to arrive adds to, and musts arrive adds an ending must does not take.
The rule requires a seatbelt. Which sentence states that requirement?
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Must wear states the requirement with a base verb. Must to wear and must wearing do not fit the core-modal frame.
One person needs an early start. Choose the have-to sentence.
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She has to get up early agrees with she and keeps to. Have to does not agree with she, and musts is not the have-to pattern.
Ask whether her early start is necessary, using have to.
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Have to makes its question with does. Does she must mixes the core modal into the do frame, and musts she to get up is not a question pattern taught here.
A sign forbids smoking in this room. Which sentence matches the sign?
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Mustn't smoke forbids smoking. Don't have to smoke only says smoking is not required, and must to smoke both uses the wrong frame and states a requirement.
The host says coming to the party is optional. Which sentence matches?
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Don't have to come means coming is not required. Mustn't come would forbid coming, and must to come is a broken requirement frame.
What does "You mustn't park here" mean on a no-parking sign?
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On this sign, mustn't forbids parking. Not required would be don't have to, and advice would use should.
Choose the advice sentence with a base verb.
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Should rest is advice with a base verb. Should to rest and should resting do not fit the core-modal frame.
Yesterday the late shift was required. Choose the past have-to sentence.
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Had to is the past of have to for this requirement. Musted is not a past form of must, and have to worked mixes the present have-to frame with a past verb.
She is required to study. Choose the core modal that does not add an ending.
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Must study keeps the base modal and a base verb. Musts adds an ending, and must to study adds to. She has to study would be the separate have-to pattern.
Keep to in the have-to pattern for a necessary departure.
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Have to go keeps to and a base verb. Have go drops to, and have going uses an -ing form.
A person asks, “Could you help me carry this box?” Which meaning fits this use of could?
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Could you help ...? makes a request in this context. It does not report a past action or establish a general requirement. Could has other uses, so read the sentence rather than treating the word alone as past time. Next try: answer the request without inventing a rule.
Swimming is allowed, and a cap is required. Which pair keeps both facts?
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Here can swim grants the stated permission; it does not prove swimming ability. Must wear keeps the cap requirement. Can to swim and must to wear add to after core modals; mustn’t swim and don’t have to wear reverse the supplied rules.
Bringing lunch is optional. Lunch is not forbidden. Which sentence fits?
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Don't have to bring lunch means lunch is not required. Mustn't would forbid it, and must to bring is a broken requirement.
The library rules forbid eating anywhere in the library. Which sentence expresses that prohibition?
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Mustn’t eat expresses the stated eating prohibition. Don’t have to eat only removes a requirement; should to eat does not form a grammatical core-modal advice frame. A ban on eating is not a general description of everything people may bring into the building.
Choose advice to drink water, with a base verb.
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Should drink is advice with a base verb. The other options add to or an -ing form.
Giving a name at the desk is required. Bringing a pen is optional. Which pair fits?
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Must give keeps the name requirement, and don’t have to bring a pen preserves the option. Don’t have to give removes the requirement, while mustn’t bring changes optional into forbidden. Must to give and should to bring add to after core modals.
Transfer: a school trip
- The notice says students can bring a bottle of water, and they must give their name to the teacher. Water is allowed; the name is required.
- They don't have to bring food. That sentence does not forbid food, but it does not by itself state every permission either. Attempt the new workshop message before opening its model, then compare the actual notice and full frames.
On the school bus, phones are forbidden. A packed lunch is optional. Which sentence keeps both facts?
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Mustn’t use a phone keeps the bus prohibition; don’t have to bring lunch keeps the option. Don’t have to use a phone/mustn’t bring lunch swaps these meanings. Must to use and should to bring add to and do not give the stated rules.
At the museum, bags may be left in the cloakroom, and a name is required at the door. Which pair fits?
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Can leave a bag grants the stated permission; must give your name keeps the requirement. Must to leave/can to give add to after core modals. Mustn’t leave forbids the bag, and don’t have to give removes the name requirement.
Workshop notes: name badge—required during the whole workshop; phone use—forbidden during the demonstration; notebook—allowed but optional. Write three English sentences reporting these rules using must, mustn’t and don’t have to. Preserve the times and meanings. Compare and revise.
Compare your English with the notes and checklist. Repair a real form or meaning mismatch, or explain why none is present. Several answers can fit. This self-review does not automatically mark correctness or establish proficiency.
Return later
- Tomorrow, recall one ability, one piece of advice, one requirement, and the split between mustn't and don't have to before you reread. Then try the later-review choices.
- Use the new art-room notes to distinguish given permission/requirements from a question still unanswered. Continue with prepositions and connectors. A written self-review does not establish correctness or certify proficiency.
Usage guidance checked 2026-10-20: Cambridge, have to and must, can and British Council, permission and obligation. Local source checks; independent language, answer and learner review pending.
Recall the base verb after can: I can ___.
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Can swim uses the base verb. To swim and swimming do not complete this core-modal frame.
A sign forbids smoking. A second line says a jacket is optional. Which pair keeps both lines?
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Mustn’t smoke keeps the prohibition. Don’t have to wear a jacket keeps no requirement. Don’t have to smoke/mustn’t wear a jacket swaps the rules. Must to smoke/should to wear adds to after core modals and does not preserve the notice.
Return later without rereading. Art-room notes: water bottles—allowed; washing brushes after use—required; whether you must bring your own paint—unknown. Write an English can sentence for permission, a have-to statement for the requirement and a have-to question about bringing paint. Do not invent the answer. Compare and revise.
Compare your English with the notes and checklist. Repair a real form or meaning mismatch, or explain why none is present. Several answers can fit. This self-review does not automatically mark correctness or establish proficiency.