No future or perfect form: Use be able to: “I’ll be able to come tomorrow.” / “I haven’t been able to sleep.”
No -s, no to: “He can swim”, not “He cans swim” or “He can to swim”.
Examples
I can drive, but I don’t have a car.
Ability
Can I use your phone?
Informal permission
This word can have two meanings.
Possibility
We can’t park here.
Negative
Tip: For one specific success in the past, use “was able to” or “managed to”, not “could”: “Despite the traffic, we managed to arrive on time.”
Common mistakes
✗She cans swim.
✓She can swim.
Modals never take -s.
✗I will can come.
✓I’ll be able to come.
Two modals cannot follow each other.
✗I can to help.
✓I can help.
Modal + base verb, no to.
Form
Positive
Subject + could + base verb
Negative
Subject + could not / couldn’t + base verb
Question
Could + subject + base verb?
How it works
General past ability: I could read when I was four.
One past success: Use was able to / managed to: “We managed to finish on time.” Not “We could finish on time.”
Possibility: It could rain later. / This could be the answer.
Polite permission and requests: Could I open the window? / Could you pass the salt?
Suggestions: You could try restarting the phone.
Deduction: She could be at home — I’m not sure.
could have + past participle: Past possibility or missed opportunity: “I could have helped, but I didn’t know.”
Examples
When I was a child, I could climb that tree.
General past ability
Could you speak more slowly, please?
Polite request
The keys could be in the kitchen.
Possibility
You could have told me!
Missed opportunity / criticism
Tip: “Could” is more polite than “can” for requests. For past obligation and past probability, use “had to” and “must have”.
Common mistakes
✗I could finish the report yesterday.
✓I was able to finish the report yesterday.
One completed success takes was able to / managed to.
✗I could to swim.
✓I could swim.
Modal + base verb.
Form
Positive
Subject + may + base verb
Negative
Subject + may not + base verb
Question
May + subject + base verb?
How it works
Formal permission: May I come in? / Students may use the library until 9 p.m.
Possibility: It may rain this afternoon. (About 50% certainty.)
Formal concession: However hard he may try, he won’t finish today.
Wishes: May you have a happy birthday. (formal or literary)
Past possibility: may have + past participle: “She may have missed the bus.”
Reported speech: “You may leave” → He said we might leave.
Examples
May I ask a question?
Formal permission
The results may take a few days.
Possibility
There may be a simpler solution.
Possibility
She may have forgotten the meeting.
Past possibility
Tip: “May” is more formal than “can” for permission. In everyday speech, “can” is far more common.
Form
Positive
Subject + might + base verb
Negative
Subject + might not / mightn’t + base verb
Question
Might + subject + base verb? (formal)
How it works
Weaker possibility: She might be at work. (More uncertain than “may”.)
Very polite request: Might I ask a question? (Very formal, uncommon in speech.)
Tentative suggestion: You might want to check the settings.
Deduction about the past: He might have missed the train.
Formal purpose: I left early so that I might catch the train.
Reported “may”: “You may go” → She said we might go.
Examples
I might go to the gym later.
Possible plan
They might not arrive before dark.
Negative possibility
You might have left your keys in the car.
Past possibility
Might I make a suggestion?
Very formal
Tip: Use “might” when you are less sure than “may”. For strong certainty, use “must”; for impossibility, use “can’t”.
Common mistakes
✗She might to come.
✓She might come.
Modal + base verb.
✗She might comes.
✓She might come.
No -s after a modal.
Form
Positive
Subject + must + base verb
Negative (prohibition)
Subject + must not / mustn’t + base verb
Question
Must + subject + base verb? (rare; use have to)
How it works
Strong obligation: I must finish this tonight. (The speaker feels it is necessary.)
Rules and laws: You must wear a seat belt.
Confident deduction: You must be tired after that journey.
Prohibition: You mustn’t smoke here. (= it is not allowed)
No past or future form: Use had to / will have to: “I had to work late.” / “I’ll have to leave early.”
Must vs have to: must often comes from the speaker; have to often comes from an external rule or situation.
Examples
I must call my mother tonight.
Personal obligation
Passengers must show their tickets.
Official rule
He must be at work — his car is here.
Deduction
You mustn’t touch that switch.
Prohibition
Tip: “Mustn’t” is a prohibition. For “not necessary”, use “don’t have to” or “needn’t”: “You don’t have to come” = you can stay away; “You mustn’t come” = you are not allowed to come.
Common mistakes
✗I must to go now.
✓I must go now.
Modal + base verb.
✗I musted work late.
✓I had to work late.
Must has no past form.
✗You mustn’t to smoke.
✓You mustn’t smoke.
No to after a modal.
✗I don’t must go.
✓I don’t have to go.
Use have to for negative obligation.
Form
Positive
Subject + should + base verb
Negative
Subject + should not / shouldn’t + base verb
Question
Should + subject + base verb?
How it works
Advice: You should see a doctor about that cough.
Expectation: The train should arrive at six.
Probable deduction: She should be home by now. (I expect so.)
Conditional: If you should need help, call me. (formal)
should have + past participle: Regret or criticism: “You should have told me.” / “I should have studied more.”
After suggest / recommend: “I suggest that he should see a specialist.” (BrE; the subjunctive “see” is also correct.)
Examples
You should drink more water.
Advice
They should have arrived by now.
Expectation
You shouldn’t work so late.
Negative advice
He should have apologised.
Criticism of the past
Tip: Should = it is a good idea. Must = it is necessary. Have to = it is required by a rule or situation.
Common mistakes
✗You should to rest.
✓You should rest.
Modal + base verb.
✗You should have came.
✓You should have come.
Past participle after have.
Form
Positive
Subject + ought to + base verb
Negative
Subject + ought not to / oughtn’t to + base verb
Question
Ought + subject + to + base verb? (rare)
How it works
Advice and duty: You ought to apologise to her.
Expectation: The film ought to be good — it got great reviews.
Past criticism: ought to have + past participle: “You ought to have warned me.”
Formality: Slightly more formal than “should”; less common in questions and negatives.
Examples
We ought to leave before the traffic gets bad.
Advice
He ought not to eat so much sugar.
Negative advice
They ought to be here soon.
Expectation
She ought to have checked the figures.
Past criticism
Tip: “Ought” always takes “to”, unlike other modals. In everyday speech, “should” is usually more natural.
Common mistakes
✗You ought rest.
✓You ought to rest.
Ought always takes to.
✗You ought to have went.
✓You ought to have gone.
Past participle after have.
Form
Positive
Subject + will + base verb
Negative
Subject + will not / won’t + base verb
Question
Will + subject + base verb?
How it works
Future: I’ll call you tomorrow.
Willingness and promises: I’ll help you. / I won’t tell anyone.
Requests: Will you close the door, please?
Refusal: The car won’t start. / She won’t listen.
Habits and characteristics: She’ll sit for hours reading. (present habit, emphatic)
Certainty about the present: That’ll be the postman. (= that is probably the postman)
No “to”: “I will to go” is wrong; use “I will go”.
Examples
I’ll send the email this afternoon.
Future
I’ll carry that for you.
Offer
He won’t answer his phone.
Refusal
Will you be quiet, please?
Request
Tip: For arrangements, use the present continuous (“I’m meeting Sam at 6”); for timetables, the present simple (“The train leaves at 8”).
Common mistakes
✗I will to help.
✓I’ll help.
Modal + base verb.
✗She will comes.
✓She will come.
No -s after a modal.
Form
Positive
Subject + would + base verb
Negative
Subject + would not / wouldn’t + base verb
Question
Would + subject + base verb?
How it works
Past habits: We would play outside every summer. (Repeated actions only — not states.)
Polite requests and offers: Would you like some tea? / Would you close the window?
Conditional: I would travel more if I had the time.
Reported speech: “I will come” → He said he would come.
Future in the past: We didn’t know the film would be so long.
would have + past participle: Third conditional: “If I had known, I would have called.”
Preferences: I’d rather stay home. / I’d prefer to walk.
Examples
When I was young, we would visit my grandparents every Sunday.
Past habit
Would you mind opening the window?
Polite request
I wouldn’t do that if I were you.
Advice with conditional
She said she would send it later.
Reported future
Tip: Use “used to” for past states (“I used to live in Rome”) and either “used to” or “would” for repeated past actions (“I used to/would play there”).
Common mistakes
✗I would live in Rome when I was a child.
✓I used to live in Rome when I was a child.
Would is not used for past states.
✗I would have went.
✓I would have gone.
Past participle after have.
✗Would you mind to open the window?
✓Would you mind opening the window?
Would you mind + -ing.
Form
Positive
Subject + shall + base verb
Negative
Subject + shall not / shan’t + base verb
Question
Shall + I/we + base verb?
How it works
Offers and suggestions: Shall I open the window? / Shall we go now?
Formal rules and contracts: The tenant shall pay the rent on the first day of each month.
Formal future (BrE): I shall return tomorrow. (Formal and increasingly rare.)
Register: Uncommon in modern American English; “should” and “will” usually replace it outside offers and legal texts.
Examples
Shall I help you with that?
Offer
Shall we meet at seven?
Suggestion
The company shall provide all necessary training.
Formal rule
I shan’t be long.
Formal negative
Tip: Use “Shall I/we …?” for offers and suggestions. For ordinary future statements, “will” is safer in international English.
Form
Positive
Subject + have/has to + base verb
Negative (no obligation)
Subject + don’t/doesn’t have to + base verb
Question
Do/Does + subject + have to + base verb?
Past
Subject + had to + base verb
How it works
External obligation: I have to wear a uniform at work.
Rules and circumstances: We had to leave early because of the storm.
Past and future: had to / will have to / have had to: “I’ll have to renew my passport.”
No obligation: You don’t have to come. (= it isn’t necessary)
Prohibition: You mustn’t come. (= you are not allowed) — a very different meaning!
Informal “have got to”: I’ve got to go now. (Common in speech.)
Examples
She has to start work at 8 a.m.
External rule
We had to wait two hours.
Past obligation
You don’t have to pay today.
No obligation
Do you have to work this weekend?
Question
Tip: must and have to are close in meaning. Use have to when you need a past or future form, or when the obligation comes from outside.
Common mistakes
✗I don’t must go.
✓I don’t have to go.
Use have to for negative obligation.
✗I have to going now.
✓I have to go now.
have to + base verb.
✗She has to works.
✓She has to work.
No -s on the main verb.
Form
Necessity
Subject + need(s) to + base verb
No necessity
Subject + don’t/doesn’t need to + base verb
Modal negative
Subject + needn’t + base verb (BrE)
Modal question
Need + subject + base verb? (formal)
How it works
Necessity: I need to study tonight.
No necessity: You don’t need to worry. / You needn’t worry.
Formal modal use: Need I say more? / Nobody need know.
didn’t need to vs needn’t have done: “I didn’t need to book” = it wasn’t necessary (probably no booking). “I needn’t have booked” = I booked, but it wasn’t necessary.
need + noun / -ing: The car needs a service. / The car needs washing. (BrE)
Examples
You need to show your ID at reception.
Necessity
We needn’t have taken a taxi — the station was five minutes away.
Unnecessary past action
Does she need to bring anything?
Question with do-support
The plants need watering.
need + -ing
Tip: Use “don’t need to” or “needn’t” for no obligation. Do not confuse them with “mustn’t” (prohibition).
Common mistakes
✗You needn’t to worry.
✓You needn’t worry.
Modal need takes no to.
✗She need to go.
✓She needs to go.
As a normal verb, need takes -s.
Form
Positive
Subject + be able to + base verb
Negative
Subject + not be able to + base verb
Question
Be + subject + able to + base verb?
How it works
Future ability: I’ll be able to come tomorrow. (Not “I will can”.)
Perfect ability: I haven’t been able to sleep lately.
After another modal: You might be able to fix it.
Infinitive and -ing: I’d like to be able to swim. / Being able to work remotely is useful.
Specific past success: We were able to escape through the window. (= managed to)
Examples
She’s able to work from anywhere.
Present ability
Will you be able to join us?
Future
We weren’t able to find the address.
Past
I’ve been able to save some money this year.
Present perfect
Tip: Use “be able to” whenever “can” cannot go: after will, have, might, to, or in the perfect tenses.
Common mistakes
✗I will can help.
✓I’ll be able to help.
No two modals together.
✗I would like to can swim.
✓I’d like to be able to swim.
Can has no infinitive.
Form
Positive
Subject + used to + base verb
Negative
Subject + didn’t use to + base verb
Question
Did + subject + use to + base verb?
How it works
Past habits: I used to play football every weekend.
Past states: She used to live in Rome. / There used to be a shop here.
Only the past: For present habits, use the present simple: “I play football every weekend.”
Negative and question: “I didn’t use to like coffee.” / “Did you use to live here?” (No -d in “use”.)
be used to + -ing: A different structure meaning “be accustomed to”: “I’m used to getting up early.”
Examples
We used to go camping every summer.
Past habit
He used to be a teacher.
Past state
Did you use to play the piano?
Question
She’s used to working under pressure.
Accustomed to
Tip: Do not mix the two structures: “used to + base verb” (past habit) vs “be used to + -ing” (accustomed).
Common mistakes
✗I used to playing tennis.
✓I used to play tennis.
used to + base verb.
✗I am used to play tennis.
✓I am used to playing tennis.
be used to + -ing.
✗Did you used to live here?
✓Did you use to live here?
No -d after did.
Form
Positive
Subject + had better (’d better) + base verb
Negative
Subject + had better not + base verb
How it works
Strong advice: You’d better see a doctor. (Or the problem may get worse.)
Warning: We’d better leave now, or we’ll miss the train.
Form: “Had” does not refer to the past. It is always followed by the base verb: “You’d better go.”
Negative: You’d better not tell him.
Register: Common in speech; “should” is more neutral in writing.
Examples
You’d better take an umbrella — it looks like rain.
Advice
We’d better not be late again.
Negative warning
He’d better apologise.
Strong expectation
Tip: Use “had better” when there is a clear consequence if the advice is ignored. Otherwise, “should” is softer and more general.
Common mistakes
✗You had better to go.
✓You’d better go.
No to after had better.
✗You better to go.
✓You’d better go.
Keep had in formal writing; “you better go” is very informal.
How it works
1. Modal + base verb: No to, no -s, no -ed, no -ing: “She can swim”, not “She cans swim” or “She can to swim”.
2. No do-support: Questions and negatives are formed with the modal itself: “Can you help?” not “Do you can help?”; “He can’t come” not “He doesn’t can come”.
3. One modal at a time: Use a semi-modal or another structure: “I’ll be able to come” (not “I will can come”); “You might have to wait” (not “You might must wait”).
4. No person changes: Modals are the same for all subjects: I can, she can, they must.
5. Semi-modals behave differently: Have to, need to, ought to, used to and be able to take to and change with tense and person: “She has to work”, “I had to work”.
Examples
He can speak Japanese.
No -s
Can I sit here?
No do-support
We’ll have to leave early.
Semi-modal for future obligation
She has been able to relax.
Perfect form
Tip: If you need two modal meanings, use a semi-modal for one of them: “You might have to wait” (= possibility + obligation).
Common mistakes
✗Do you can drive?
✓Can you drive?
No do-support with modals.
✗She musts go.
✓She must go.
Modals never take -s.
✗I will can help.
✓I’ll be able to help.
No two modals together.
How it works
must + base verb: almost certain (positive deduction) — “He must be at work.”
should / ought to + base verb: probable, expected — “She should be home by now.”
may / might / could + base verb: possible but uncertain — “It may rain later.”
can’t + base verb: almost impossible (negative deduction) — “That can’t be true.”
For deductions about the past, add have + past participle: “He must have forgotten.”
Certainty scale
Certainty
Modal
Example
≈ 95%
must
You must be exhausted.
≈ 80–90%
should / ought to
The parcel should arrive today.
≈ 50%
may
It may snow tonight.
≈ 30–50%
might / could
She might call later.
≈ 0% (negative)
can’t
That can’t be the right answer.
Examples
The lights are on — they must be home.
Very confident
They should be here by eight.
Expected
She might be in a meeting.
Possible
He can’t be serious.
Impossible
Tip: “Mustn’t” is a prohibition, not a negative deduction. For “it is impossible”, use “can’t”: “He can’t be at home — I just saw him at work.”
Common mistakes
✗He mustn’t be at home — I saw him leave.
✓He can’t be at home — I saw him leave.
Use can’t for negative deduction.
How it works
must have + past participle: A confident deduction about the past: “You must have been tired.”
might / may / could have + past participle: A past possibility: “She might have missed the bus.”
can’t / couldn’t have + past participle: Something was impossible: “They can’t have arrived yet.”
should / ought to have + past participle: Regret or criticism: “You should have called me.”
could have + past participle: An unused possibility or missed opportunity: “I could have helped, but I didn’t know.”
needn’t have + past participle: You did something that was not necessary: “You needn’t have bought milk — we have plenty.”
would have + past participle: An unreal past result: “If I had known, I would have come.”
Past obligation: Use had to, not “must have”: “I had to work late yesterday.”
Table
Structure
Meaning
Example
must have done
Certain about the past
He must have forgotten.
may/might/could have done
Possible in the past
She might have left.
can’t have done
Impossible in the past
They can’t have finished already.
should/ought to have done
Regret or criticism
You should have asked.
could have done
Unused possibility
I could have stayed longer.
needn’t have done
Did it unnecessarily
We needn’t have paid.
would have done
Unreal past result
I would have gone.
Examples
She must have left her keys at home.
Certain deduction
They might have taken the wrong train.
Possible past
You should have told me earlier.
Criticism
I needn’t have worried — the exam was easy.
Unnecessary worry
We could have won if we had practised more.
Unreal past
Tip: The pronunciation of “have” is weak (/əv/), so “should have” sounds like “should’ve”. Never write “should of”.
Common mistakes
✗You should of told me.
✓You should have told me.
“Of” is not a verb.
✗You should have came.
✓You should have come.
Past participle after have.
✗I must have went.
✓I must have gone.
Past participle.
How it works
Informal: Can you help me?
Polite: Could you help me?
Very polite: Would you mind helping me? (Answer: “Not at all.”)
Tentative: Do you think you could help me?
Formal permission: May I ask a question?
Very formal: I was wondering if you could help me.
Offers: Can I help? / Shall I carry that? / Would you like some tea?
Politeness ladder
Register
Request
Typical answer
Informal
Can you …?
Sure.
Polite
Could you …?
Of course.
Very polite
Would you mind …ing?
Not at all.
Tentative
Do you think you could …?
I’ll try.
Formal permission
May I …?
Yes, you may.
Very formal
I was wondering if you could …
Certainly.
Examples
Could you send me the file?
Everyday polite
Would you mind closing the door?
Very polite
May I come in?
Formal permission
I was wondering if you could check this.
Indirect and tentative
Tip: With “Would you mind …ing?”, a negative answer means yes, I will do it: “Not at all” = I don’t mind = I’ll help.
How it works
Adding to after a modal: “must to go”, “can to swim”, “should to rest”.
Adding -s: “She cans”, “He musts”.
Using do-support: “Do you can …?”, “I don’t must …”.
Two modals together: “will can”, “might must”.
Confusing mustn’t (prohibition) with don’t have to (no obligation).
Using must for past obligation: “I musted” → “I had to”.
Mixing used to + base verb with be used to + -ing.