Key features

• No inflection

Modals do not take -s in the third person singular, past or -ing form.

✅She can swim. 

❌She cans swim. 

• Followed by the bare infinitive

They are always followed by the base form of the main verb (without to).

You must finish on time.

• Negation and questions without auxiliaries

Modals form negatives and questions without using "do".

• Can you help? (Do you can help? ❌)

• You shouldn’t worry.

Modal verbs overview

CAN / COULD / BE ABLE TO

Can

1. Ability in the present or in general: Can is the most common way to talk about skills and capacities. It applies both to things people have learned (skills) and to natural abilities.

• I can play the guitar, but I can’t play the piano. (learned skill) 

• Owls can see in the dark. (natural ability)

2. Permission (informal, spoken English): Can is often used to allow or forbid someone to do something. It’s common in everyday contexts, though may is more formal.

• You can leave early today. (permission granted)

• Sorry, you can’t come in without a ticket. (permission denied)

3. Possibility (general, objective): Can expresses that something is possible, without necessarily referring to a specific occasion — often for things that are true sometimes or in general.

• Life can be very unpredictable. 

4. Requests and offers (informal): With can, requests and offers sound direct and friendly, but sometimes less polite than could or may.

• Can you help me with this exercise? (request)

• Can I carry that bag for you? (offer)

Could

1. Past ability (general, not specific events): Could describes abilities people had in the past, especially during a period of time, not on one occasion.

• When I was a child, I could run very fast. (general past ability) 

• She could read when she was four. (ability at a young age)

• ❌ I could pass the exam yesterday. → Wrong, because the exam is a specific occasion. Use was able to.

2. Polite requests and permission: Could is softer and more polite than can. It sounds more formal, careful, or respectful.

• Could you open the window, please? (polite request)

• Could I speak to Mr. Smith, please? (polite permission)

3. Possibility in the present or future (less certain than can): Could suggests that something is possible, but less definite than can.

• It could rain later. (uncertain, but possible)

• That could be true, though I’m not sure. (tentative opinion)

4. Hypothetical ability (imagined situations): Could is used in conditional sentences or when imagining abilities in unreal situations.

• I could help you if you explained the problem.

Be able to

1. General or specific ability in all tenses: Unlike can/could, be able to is flexible and can be used in any tense (present, past, perfect, future).

• I am able to solve this problem. (present)

• She has been able to find a job recently. (present perfect)

• He will be able to attend the meeting. (future)

• By next year, I’ll have been able to save enough money. (future perfect)

2. Specific ability in the past (when “could” doesn’t work): Could describes general ability in the past, but for one-time successful actions, was able to is the correct choice.

• The fire was very strong, but they were able to escape. (they managed to do it on that occasion)

3. Formal/academic tone: In more formal writing, be able to often replaces can because it sounds less casual. It also allows for a wider range of tenses.

• The new system will be able to handle 10,000 requests per second. (technical/formal context)

MUST / HAVE TO

Must

1. Strong Obligation (internal or speaker-imposed): Must expresses a necessity that feels urgent, strong, or imposed by the speaker/authority.

• You must finish your assignment before the deadline. (urgent)

• You must wear a seatbelt at all times. (law/authority)

• I must remember to call my grandmother. (self-imposed obligation)

2. Rules and Regulations (formal): Used in instructions, official documents, and notices.

• Candidates must arrive at least 15 minutes early.

3. Strong Deduction / Logical Conclusion: Expresses certainty (present or past) when we have strong evidence.

• You must be tired after such a long journey. (present deduction)

• She must have forgotten our meeting. (past deduction)

Have to

1. External Obligation (rules, necessity outside speaker’s control): Refers to obligations coming from circumstances, rules, or external authority rather than the speaker.

• I have to wear a uniform at school. (rule)

• She has to submit the form by Friday. (external authority)

2. Everyday Necessity (neutral, less formal than must): Sounds more natural in daily conversation than must.

• Sorry, I can’t stay. I have to catch the train.

3. For Past, Future, and Questions: Unlike must, have to works in all tenses and questions:

• Past: I had to cancel my trip.

• Future: You will have to show ID at the airport.

• Question: Do I have to attend the meeting?

4. No Strong Deduction: Have to is NOT normally used for deductions.

• ❌ She has to be tired. → sounds like obligation, not logical conclusion.

• ✅ She must be tired. → deduction

WILL / WOULD

Will

1. Future predictions (neutral or certain): Refers to what the speaker sees as certain or inevitable. It is also used for the 1st Conditional. 

• The sun will rise at 6:30 tomorrow. 

• Prices will increase if inflation continues.

2. Spontaneous decisions: When the decision is made at the moment of speaking.

• I’ll answer the phone.

• Don’t worry, I’ll help you with your bags.

3. Promises and threats: Used to show determination, insistence, or threat:

• I will always love you. (promise)

• You’ll regret this decision. (threat)

4. Orders / instructions: Especially in formal or military-like contexts, will expresses obligation in the form of an order.

• You will stay here until I return.

• All students will hand in their essays by Friday.

Would

1. Polite requests / offers: It is more formal and softer petitions than will.

• Would you like a cup of tea?

• I would be happy to help.

2. Hypothetical or unreal situations: It is used for making hypothesis about unlikely or impossible situations - 2nd and 3rd Conditional. 

• If I had more time, I would travel the world.

• She would have bought it if it had been cheaper.

3. Past habits (like "used to"):  Repeated actions in the past, especially with nostalgia.

• When we were kids, we would spend hours playing outside.

• Every summer, they would go camping in the mountains.

4. Future in the past: Talking about the future from a past point of view. (Reported Speech)

• He said he would call me the next day.

• They promised they would send the documents.

SHALL / SHOULD / OUGHT TO

Shall

1. Suggestions and offers (mainly in questions): In British English, "shall" is often used for making offers or suggestions, particularly in a more formal or polite context.

• Shall I help you with your bags?

• Shall we start the meeting now?

2. Formal rules, contracts, and legal language: In legal or formal contexts, "shall" is often used to express obligation, indicating what is required or must be done. 

• All visitors shall sign in at reception.

• The company shall provide training for all employees.

3. Formal determination or promise (literary/ceremonial):  In literature or speeches, "shall" conveys authority and solemnity. It gives a sense of finality or moral determination.

• You shall not pass!

Should

1. Advice / recommendation: Should is used to give suggestions or recommendations in a polite but clear way.

• You should see a doctor.

2. Light obligation / duty: Expresses what is morally right or socially expected, though not legally binding. 

• Employees should treat customers with respect.

3. Expectation / probability:  Used when something is likely or expected to happen, though not guaranteed.

• The train should arrive at 7.45.

Ought to

1. Advice / recommendation: Polite suggestion, often slightly stronger than should.

• You ought to back up your files regularly.

2. Moral duty / strong obligation: Expresses what is the right or proper thing to do, from a moral standpoint. 

• We ought to look after our planet.

3. Probability / logical expectation: Indicates that something is logically expected to be true or to happen.

• This ought to be enough money.