Grammar Rule in 30 Seconds
Use modal verbs to express your level of certainty about a situation based on evidence or logic.
- Use 'must' for near-certainty: 'He must be tired.'
- Use 'might/may/could' for possibility: 'She might be late.'
- Use 'can't' for near-certainty of impossibility: 'It can't be true.'
Overview
- Nobody is answering — they must be busy.
- She knows every answer. She must have studied all night.
- He looks exhausted. He must have been travelling all night.
- She can't be the director — she looks about twenty.
- The payment can't have gone through — it was declined.
- The report should be ready by now.
- The guests ought to have arrived — let me call them.
- The medicine should work within 48 hours.
- The delay could be due to a system failure.
- They may have taken a different route.
- It might be worth reconsidering the approach.
- This may well turn out to be the best decision we ever made.
- With that much preparation, she is bound to do well.
- There are bound to be complications at some point.
Modal Probability Formation
| Certainty | Present | Past |
|---|---|---|
|
High (Positive)
|
Must + Verb
|
Must + have + P.P.
|
|
High (Negative)
|
Can't + Verb
|
Can't + have + P.P.
|
|
Possibility
|
Might/May/Could + Verb
|
Might/May/Could + have + P.P.
|
Common Contractions
| Full Form | Contraction |
|---|---|
|
Cannot
|
Can't
|
|
Could not
|
Couldn't
|
|
Might have
|
Might've
|
Meanings
Modal verbs of probability are used to express how certain we are about a deduction or a situation.
Logical Deduction
Concluding something is true based on evidence.
“She's wearing a coat, so it must be cold.”
“He's not answering; he might be in a meeting.”
Possibility
Expressing that something is possible but not certain.
“It could rain later.”
“They may arrive by noon.”
Impossibility
Expressing that something is logically impossible.
“That can't be right.”
“It couldn't have been him.”
Reference Table
| Form | Structure | Example |
|---|---|---|
|
Affirmative (Present)
|
Subject + must + verb
|
He must be tired.
|
|
Affirmative (Past)
|
Subject + must + have + P.P.
|
He must have been tired.
|
|
Negative (Present)
|
Subject + can't + verb
|
He can't be tired.
|
|
Negative (Past)
|
Subject + can't + have + P.P.
|
He can't have been tired.
|
|
Possibility (Present)
|
Subject + might + verb
|
He might be tired.
|
|
Possibility (Past)
|
Subject + might + have + P.P.
|
He might have been tired.
|
正式程度
He may be in his office. (Workplace)
He might be in his office. (Workplace)
He's probably in his office. (Workplace)
He's likely at his desk. (Workplace)
Certainty Scale
High
- Must 100% sure
Possibility
- Might 50% sure
Impossibility
- Can't 0% sure
按水平分级的例句
It might rain.
It might rain.
He may be home.
He may be home.
That can't be right.
That can't be right.
It must be cold.
It must be cold.
They must have left.
They must have left.
She could be at work.
She could be at work.
It can't be true.
It can't be true.
He might have forgotten.
He might have forgotten.
He must be working late again.
He must be working late again.
They might have been delayed by traffic.
They might have been delayed by traffic.
That couldn't have been him; he's in London.
That couldn't have been him; he's in London.
She may have already finished the report.
She may have already finished the report.
The project must have been completed by now.
The project must have been completed by now.
It could be that they are waiting for us.
It could be that they are waiting for us.
He can't have seen the email yet.
He can't have seen the email yet.
They might be considering our proposal.
They might be considering our proposal.
He must have been working on this for weeks.
He must have been working on this for weeks.
It could have been a misunderstanding, but I doubt it.
It could have been a misunderstanding, but I doubt it.
They may well have decided to postpone the event.
They may well have decided to postpone the event.
That can't have been the only reason for his departure.
That can't have been the only reason for his departure.
One might have expected a more favorable outcome.
One might have expected a more favorable outcome.
It could not but have been a deliberate choice.
It could not but have been a deliberate choice.
They must be being watched by the authorities.
They must be being watched by the authorities.
He may have been misinformed, or perhaps he lied.
He may have been misinformed, or perhaps he lied.
容易混淆
Learners mix up 'I must go' (obligation) and 'He must be home' (deduction).
Learners use 'mustn't' for negative deduction.
Learners think they have different meanings.
常见错误
He must to be home.
He must be home.
He musts be home.
He must be home.
It mustn't be true.
It can't be true.
He might be go.
He might go.
He must have be home.
He must have been home.
He can be not home.
He can't be home.
It might be rain.
It might rain.
He must have went.
He must have gone.
He could have go.
He could have gone.
It must be have been.
It must have been.
He must have been being there.
He must have been there.
It might have been to be true.
It might have been true.
He can't have to be there.
He can't be there.
It must be that he has been.
He must have been.
句型
He ___ be at home.
They ___ have forgotten the meeting.
It ___ be true; I saw it myself.
She ___ have been working all night.
Real World Usage
She must be having a great time!
Might be late, sorry!
We could look into that strategy.
The flight might be delayed.
The driver must be lost.
These findings may suggest a correlation.
Context is King
Mustn't Trap
Use 'Can't' for Negative
Politeness
Smart Tips
Use 'might' to hedge your statement and sound more natural.
Use 'must' to show you have reached a logical conclusion.
Always use 'can't' instead of 'mustn't'.
Remember to add 'have' + past participle.
发音
Contractions
In spoken English, 'might have' often becomes 'might've' (/maɪtəv/).
Stress
Modals are usually unstressed unless you want to emphasize the certainty.
Falling
He MUST be home. ↘
Strong conviction.
记住它
记忆技巧
Must is a Must-have for certainty; Might is for Maybe.
视觉联想
Imagine a detective with a magnifying glass. If they see a footprint, they say 'It MUST be him!' If they see a shadow, they say 'It MIGHT be him.'
Rhyme
If you're sure, use must, if you're not, use might, if it's impossible, use can't to be right.
Story
Detective Miller looked at the empty safe. 'The thief must have had a key,' he said. 'He might have entered through the window,' his partner suggested. 'No, the window is locked; it can't have been the window.'
Word Web
挑战
Look around your room and make 5 guesses about your belongings using different modals.
文化笔记
British speakers often use 'might' more frequently than 'may' to sound less formal.
Americans often use 'probably' instead of modals for probability in casual speech.
In academic writing, 'may' is preferred for hedging claims.
Modal verbs evolved from Old English preterite-present verbs.
对话开场白
Why is the office empty today?
Who do you think left this bag here?
Why didn't he show up to the meeting?
What do you think caused the market crash?
日记主题
常见错误
Test Yourself
He ___ be home; his car is in the driveway.
Which sentence is correct?
Find and fix the mistake:
It mustn't be true.
He must be tired. -> He ___ tired.
A: Why is the store closed? B: It ___ a holiday.
Match each item on the left with its pair on the right:
they / must / have / forgotten
I'm not sure, but it ___ rain.
Score: /8
练习题
8 exercisesHe ___ be home; his car is in the driveway.
Which sentence is correct?
Find and fix the mistake:
It mustn't be true.
He must be tired. -> He ___ tired.
A: Why is the store closed? B: It ___ a holiday.
Match 'must' to its meaning.
they / must / have / forgotten
I'm not sure, but it ___ rain.
Score: /8
常见问题 (8)
No, 'must' for deduction is for present or past. Use 'might' or 'will' for the future.
Yes, 'may' is often used in formal writing, while 'might' is common in speech.
'Mustn't' is reserved for prohibition. Use 'can't' instead.
They are very similar, but 'could' sometimes implies a slightly higher possibility.
Yes, 'He must be working' is perfectly fine.
Yes, they are standard across all major English dialects.
Use 'couldn't have' or 'can't have'.
Rarely, but some literary forms use 'shall' for probability.
Scaffolded Practice
1
2
3
4
Mastery Progress
Needs Practice
Improving
Strong
Mastered
In Other Languages
Deber + infinitive
Spanish uses the conditional tense for probability, which English doesn't.
Devoir
French uses the conditional for uncertainty.
Modalverben
German word order changes with modals.
Kamoshirenai
Japanese does not use auxiliary verbs in the same way.
Yajib an
Arabic lacks a direct modal system like English.
Keneng
Chinese verbs do not conjugate for modals.
Learning Path
Prerequisites
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