English Modal Verbs: The Complete Guide

English Modal Verbs

This article provides a comprehensive, all-in-one guide to English modal verbs (can, could, may, might, must, shall, should, will, would), designed for learners at levels A1 to B1 who want to speak with confidence and precision.

The essential idea you must understand is that modal verbs are "helper" verbs that express possibility, ability, permission, obligation, necessity, and prediction. They never change form and are always followed by the base form of the main verb.

You will discover why the incorrect She can to swim. becomes the correct She can swim., and how mastering just nine modal verbs can dramatically improve your English fluency.

The key question to keep in mind is: What is the speaker's attitude or intention — ability, possibility, permission, obligation, or prediction?

The main rule to remember is: Modal verbs NEVER change form (no -s, -ed, or -ing) and are ALWAYS followed by the base form (bare infinitive) of the main verb.

By the end of this lesson, you will be able to use all nine modal verbs correctly in a variety of contexts, from everyday conversations to formal writing.

What Are Modal Verbs?

Modal Verbs

The Nine English Modal Verbs

Modal verbs are special auxiliary (helping) verbs that express attitude, mood, or intention toward an action. They don't describe actions themselves — they describe how likely, necessary, possible, or permitted an action is.

Modal VerbCore MeaningExample
canability, possibility, permissionI can swim.
couldpast ability, polite request, possibilityI could swim when I was 5.
mayformal permission, possibilityYou may leave early.
mightpossibility (less certain)It might rain today.
muststrong obligation, necessity, certaintyYou must wear a seatbelt.
shallformal suggestions, future (with I/we)I shall call you tomorrow.
shouldadvice, recommendation, expectationYou should see a doctor.
willprediction, promise, willingnessI will help you.
wouldpolite request, hypothetical situation, past habitsWould you like some tea?
💡 Important: Modal verbs are incomplete verbs. They cannot stand alone — they must be followed by another verb (the main verb) in its base form.

The Golden Rule: Modal Verbs NEVER Change

⚡ Modal verbs do not change form — no -s, -ed, or -ing!
  • ✅ She can swim. (NOT: She cans swim.)
  • ✅ He could help. (NOT: He coulded help.)
  • ✅ They must go. (NOT: They musted go.)
  • ✅ You should try. (NOT: You shoulding try.)
💡 Why? Modal verbs are finite verbs — they already carry the grammatical information (tense, person, number), so the main verb stays in its simplest form.

The Key Question: What's the Speaker's Attitude?

To choose the correct modal verb, ask yourself:

"What is the speaker's attitude — ability, possibility, permission, obligation, or prediction?"

💪 Ability

can / could

"I can speak Spanish."

❓ Possibility

may / might / could

"It might rain."

✅ Permission

can / may / could

"May I come in?"

⚠️ Obligation

must / should

"You must study."

🔮 Prediction

will / shall

"It will snow."

The Complete Rules of Modal Verbs

Rule 1: Ability — Can & Could

Can expresses present ability — what someone is able to do now. Could expresses past ability or a polite request.

✅ Can (Present Ability)

  • I can speak three languages.
  • She can run very fast.
  • We can help you.

✅ Could (Past Ability / Polite)

  • I could swim when I was 5.
  • She could read before she started school.
  • Could you help me, please?
⚠️ Important: "Can" and "could" are also used to express possibility:
  • It can be very cold here in winter. (general possibility)
  • It could snow tomorrow. (specific possibility)

Rule 2: Permission — Can, Could, & May

Can is informal permission for everyday situations. Could is a more polite request. May is formal permission, often used in official contexts.

ModalLevel of FormalityExample
CanInformal / Casual"Can I use your phone?"
CouldPolite / Slightly Formal"Could I borrow your pen?"
MayVery Formal / Official"May I come in, sir?"
💡 Pro Tip: "May" is also used to express possibility — often in formal contexts.

Rule 3: Possibility — May, Might, & Could

These three modal verbs express different levels of certainty about a possible event.

ModalLevel of CertaintyExample
May50-60% certain"It may rain later."
Might30-50% certain (less sure)"It might rain later."
CouldPurely possible"It could rain, but I'm not sure."
💡 Remember: "Might" is the least certain of the three. Use "may" when you're relatively sure, "might" when you're less sure, and "could" when it's just possible.

Rule 4: Obligation & Necessity — Must & Should

Must expresses strong obligation — something that is necessary or required. Should expresses advice or recommendation — something that is a good idea but not required.

✅ Must (Strong Obligation)

  • You must wear a seatbelt.
  • I must finish this report.
  • Students must arrive on time.

✅ Should (Advice / Recommendation)

  • You should eat more vegetables.
  • She should apologize to him.
  • We should leave early.
⚠️ Important: "Must" is much stronger than "should." "Must" means it's required. "Should" means it's a good idea but optional.

Rule 5: Prediction & Future — Will & Shall

Will is used for predictions, promises, and willingness. Shall is mostly used with "I" and "we" for formal promises or suggestions (more common in British English).

✅ Will

  • It will rain tomorrow. (prediction)
  • I will help you. (promise)
  • I will open the door. (willingness)

✅ Shall

  • I shall return soon. (formal promise)
  • Shall we go for a walk? (suggestion)
  • We shall overcome. (formal statement)
💡 Important: In modern English, "shall" is used much less frequently than "will." You can use "will" in almost all situations where "shall" used to be used.

Rule 6: Polite Requests — Would, Could, Can

Would is the most polite form. Could is also polite. Can is more casual.

ModalLevel of PolitenessExample
WouldVery polite / Formal"Would you pass me the salt?"
CouldPolite / Standard"Could you help me?"
CanCasual / Informal"Can you help me?"
💡 Pro Tip: "Would you..." is the most polite way to ask for something. Use it in formal situations or with strangers.

Examples with Deep Explanation

Example 1: "Can" — Present Ability

She can speak four languages.

Meaning: She has the ability to speak four languages. This is a present, general ability.

Why it works: "Can" expresses ability in the present. It is followed by the base verb "speak" (not "speaks").

Key question: What is the speaker's attitude? → Ability → So we use "can."

Example 2: "Could" — Past Ability

I could run very fast when I was young.

Meaning: I had the ability to run fast in the past, but I may not be able to do it now.

Why it works: "Could" expresses past ability. It is followed by the base verb "run."

Example 3: "May" — Formal Permission

May I leave early today?

Meaning: The speaker is politely asking for permission to leave early.

Why it works: "May" is a formal way to ask for permission. It is followed by the base verb "leave."

Compare: "Can I leave early?" is casual. "May I leave early?" is more formal and respectful.

Example 4: "Might" — Less Certain Possibility

We might go to the beach tomorrow.

Meaning: There is a possibility (30-50% chance) that we will go to the beach. The speaker is not sure.

Why it works: "Might" expresses a less certain possibility. It is followed by the base verb "go."

Compare: "We may go" = 50-60% sure. "We might go" = 30-50% sure.

Example 5: "Must" — Strong Obligation

You must wear a helmet when riding a bike.

Meaning: It is required/necessary to wear a helmet. There is a strong rule or obligation.

Why it works: "Must" expresses strong obligation. It is followed by the base verb "wear."

Compare: "You should wear a helmet" = advice (optional). "You must wear a helmet" = requirement (not optional).

Example 6: "Should" — Advice

You should drink more water.

Meaning: This is a recommendation. Drinking more water is a good idea, but not required.

Why it works: "Should" expresses advice or recommendation. It is followed by the base verb "drink."

Example 7: "Will" — Prediction

It will be sunny tomorrow.

Meaning: The speaker is predicting that tomorrow will be sunny. This is a forecast.

Why it works: "Will" expresses a future prediction. It is followed by the base verb "be."

Example 8: "Would" — Polite Request

Would you mind closing the window?

Meaning: This is a very polite request asking someone to close the window.

Why it works: "Would" is the most polite way to ask for something. It is followed by "you" and then the base verb "mind."

Compare: "Can you close the window?" (casual) vs "Would you close the window?" (polite).

Common Mistakes & Logical Corrections

Mistake 1: Adding "to" After a Modal

She can to swim.
She can swim.

Why Does It Change?

Modal verbs are always followed by the base form of the verb, NOT the infinitive with "to."

❌ can to swim → ✅ can swim

Remember: Modal + Base Verb (no "to").

Mistake 2: Adding "-s" to Modals with Third Person

She cans sing.
She can sing.

Why Does It Change?

Modal verbs never change form. There is no "-s," "-ed," or "-ing" with modals.

❌ cans → ✅ can

Remember: Modals are the same for all subjects (I, you, he, she, it, we, they).

Mistake 3: Using "Mustn't" Confusion

You mustn't to be late.
You mustn't be late.

Why Does It Change?

"Mustn't" means "it is forbidden" or "it is not allowed." It is followed by the base form of the verb, NOT "to" + verb.

❌ mustn't to be → ✅ mustn't be

Remember: "Mustn't" = "must not" = strong prohibition.

Mistake 4: Confusing "Must" and "Have To"

I must to go to the store.
I have to go to the store. / I must go to the store.

Why Does It Change?

"Must" is a modal verb, so it takes the base form of the verb. "Have to" is NOT a modal — it's a phrase that works like a modal but can change form.

❌ must to go → ✅ must go / have to go

Remember: "Must" + base verb. "Have to" + base verb (but "have" changes form: has to, had to).

Mistake 5: Using "Shall" in Modern English Incorrectly

They shall arrive tomorrow.
They will arrive tomorrow.

Why Does It Change?

In modern English, "shall" is rarely used except with "I" and "we" in very formal contexts. "Will" is used for all subjects in most situations.

❌ They shall → ✅ They will

Remember: Use "will" for predictions with all subjects. "Shall" is mostly used with "I" and "we" in formal contexts.

Practice Exercises

Task 1: Choose the Correct Modal

Fill in the blanks with the correct modal verb (can, could, may, might, must, should, will, would):

  • 1. I ______ swim when I was six.
  • 2. You ______ finish your homework before you go out.
  • 3. ______ I use your phone, please?
  • 4. It ______ rain tomorrow, so bring an umbrella.
  • 5. You ______ drink more water. It's good for you.

Task 2: Correct the Mistakes

Each sentence has one mistake. Find it and correct it:

  • 1. She cans speak French fluently.
  • 2. You must to wear a uniform.
  • 3. They shall arrive by 5 PM. (change to modern English)
  • 4. Could you to help me with this?
  • 5. He shoulds study more.

Task 3: Write Sentences Using Modals

Write one sentence for each of the following situations:

  • 1. Express ability (present)
  • 2. Express polite permission (formal)
  • 3. Express strong obligation
  • 4. Express advice
  • 5. Express a prediction
  • 6. Express a polite request

Task 4: Modal Verb Story

Write a short paragraph (5-7 sentences) about your plans for next week. Use at least 5 different modal verbs.

Example: "I must finish my project by Friday. I can work on it every evening. I might go to the cinema on Saturday. You should come with me. It will be fun!"

Quick Quiz

Quiz 1: The Key Question

What is the key question you should ask yourself when choosing a modal verb?

Answer

"What is the speaker's attitude — ability, possibility, permission, obligation, or prediction?"

Quiz 2: Choose the Correct Modal

Complete the sentence: "You ______ eat more vegetables."

Answer

You should eat more vegetables.

Why? This is advice or a recommendation. "Should" is the correct choice.

Quiz 3: The Golden Rule

What is the golden rule about modal verbs and form changes?

Answer

Modal verbs NEVER change form (no -s, -ed, or -ing) and are ALWAYS followed by the base form of the main verb.

Quiz 4: Find the Mistake

What is wrong with: "She can to speak three languages."

Answer

She can speak three languages.

Why? Modal verbs are followed by the base form of the verb, NOT the infinitive with "to."

Quiz 5: Write Your Own Sentence

Write a sentence using a modal verb to express strong obligation.

Model Answer

"You must wear a seatbelt when driving."

Analysis: "Must" expresses strong obligation or requirement.

Final Review: Master Modal Verbs

To complete your journey with modal verbs, review these key points and use this checklist to ensure you've mastered everything.

  • Ask the key question: What is the speaker's attitude — ability, possibility, permission, obligation, or prediction?

    Ability → can/could | Possibility → may/might/could | Permission → can/may/could
    Obligation → must/should | Prediction → will/shall
  • Remember the golden rule: Modal verbs NEVER change form. They are ALWAYS followed by the base form of the main verb.

    ✅ can swim ❌ can swims / can to swim
  • Practice using all nine modals: The more you use them, the more natural they become. Try to use at least one modal verb in every conversation.

    can • could • may • might • must • shall • should • will • would
  • Compare your sentences with correct models: Before finishing, compare your sentences with the examples in this article to catch any errors.

    Compare → Correct → Confirm

📌 Quick Summary: Modal Verbs

💪 Ability

Can / Could
"I can swim."

❓ Possibility

May / Might / Could
"It might rain."

✅ Permission

Can / May / Could
"May I come in?"

⚠️ Obligation

Must / Should
"You must go."

🔮 Prediction

Will / Shall
"It will snow."

🙏 Polite Request

Would / Could
"Would you help?"

🔑 Remember: Modal verbs NEVER change form. Modal + Base Verb (no "to"). What's your attitude — ability, possibility, permission, obligation, or prediction?

🎯 Next Step: Write a short paragraph about your plans using at least 5 different modal verbs.

Remember: "What is the speaker's attitude — ability, possibility, permission, obligation, or prediction?"

Phrasal Verbs: All-in-One tabs

Complete verb learning center

Phrasal Verbs & Other Verbs

Browse, compare, learn usage, and practice with randomized quizzes from one learning card.

7 learning sections
Choose a section above The learning content stays closed until you are ready.
Learning center is open Switch tabs at any time.
Learn combinations in context

Phrasal Verbs Library

Sort by level, base verb, primary particle, structure, meaning group, or teaching priority.

20of 359 shown

dive in

dive+in
Extended

begin an activity eagerly and without delay

Example

Once everyone is ready, we can dive in.

Grammar & classification
Two Word Inseparable Intransitive Particle: in Start Eagerly

burn out

burn+out
Common

become completely exhausted or stop working from overuse

Example

You may burn out if you work without a break.

Grammar & classification
Two Word Inseparable Intransitive Particle: out Be Exhausted

let in

let+in
Ultra Core

allow someone or something to enter

Example

Please let in the visitors.

Grammar & classification
Two Word Separable Transitive Particle: in Allow Enter

go in

go+in
Ultra Core

enter a place or vehicle

Example

Please go in and take a seat.

Grammar & classification
Two Word Inseparable Intransitive Particle: in Enter

chip in

chip+in
Extended

contribute money, effort, or ideas with other people

Example

Everyone can chip in a few dollars.

Grammar & classification
Two Word Inseparable Intransitive Particle: in Contribute

talk over

talk+over
Common

review, inspect, or discuss something carefully

Example

Let’s talk over the report one more time.

Grammar & classification
Two Word Separable Transitive Particle: over Review

fizzle out

fizzle+out
Extended

gradually become weaker and end without a strong result

Example

The discussion fizzled out after a few minutes.

Grammar & classification
Two Word Inseparable Intransitive Particle: out Fade End

pass out

pass+out
Ultra Core

lose consciousness for a short time

Example

He almost pass out because of the heat.

Grammar & classification
Two Word Inseparable Intransitive Particle: out Faint

Sense: faint.

put on

put+on
Ultra Core

put clothing or an accessory on your body

Example

You should put on a jacket before going outside.

Grammar & classification
Two Word Separable Transitive Particle: on Wear Clothing

squeeze in

squeeze+in
Extended

find space or time for someone or something in a tight schedule or place

Example

Can you squeeze in one more appointment today?

Grammar & classification
Two Word Separable Transitive Particle: in Fit Time

make up

make+up
Ultra Core

become friendly again after an argument

Example

They often argue but quickly make up.

Grammar & classification
Two Word Inseparable Intransitive Particle: up Reconcile

Sense: become friendly again.

work out

work+out
Ultra Core

solve a problem or find a satisfactory answer

Example

We can work out this problem together.

Grammar & classification
Two Word Separable Both Particle: out Solve

breathe in

breathe+in
Extended

take air into the lungs

Example

Breathe in slowly through your nose.

Grammar & classification
Two Word Inseparable Intransitive Particle: in Inhale

break down

break+down
Ultra Core

stop working because of a mechanical or system failure

Example

The car may break down if we ignore that noise.

Grammar & classification
Two Word Inseparable Intransitive Particle: down Machine Fail

Sense: machine or system failure.

check in

check+in
Ultra Core

register your arrival at a hotel, airport, event, or service

Example

We should check in at least two hours before the flight.

Grammar & classification
Two Word Inseparable Intransitive Particle: in Check Register

drift off

drift+off
Extended

gradually fall asleep

Example

I often drift off while reading at night.

Grammar & classification
Two Word Inseparable Intransitive Particle: off Doze

straighten out

straighten+out
Extended

make a situation, place, or object neat, correct, or organized

Example

We need to straighten out this room before the guests arrive.

Grammar & classification
Two Word Separable Transitive Particle: out Organize Fix

get back

get+back
Ultra Core

return to a place or previous situation

Example

We should get back before it gets dark.

Grammar & classification
Two Word Inseparable Both Particle: back Return

throw on

throw+on
Common

put clothing or an accessory on your body

Example

You should throw on a jacket before going outside.

Grammar & classification
Two Word Separable Transitive Particle: on Wear Clothing

start over

start+over
Common

start again from the beginning

Example

If this fails, we can start over.

Grammar & classification
Two Word Inseparable Intransitive Particle: over Restart