Lesson 10 – Modal Verbs: Can, Could, May & Should

What Are Modal Verbs?

A special group of auxiliary verbs with unique grammar rules

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Definition

Modal verbs are a special type of auxiliary (helping) verb. They add meaning to the main verb — expressing ability, permission, possibility, requests, or advice.

In this lesson, you will study four modals: CAN (ability/informal permission), COULD (past ability / polite requests), MAY (formal permission / possibility), and SHOULD (advice / recommendation).

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Lesson Objectives

Understand the grammar rules all modal verbs share (no -s, no -ing, no to-infinitive).
Use CAN for ability, informal permission, and requests.
Use COULD for past ability and to make polite requests.
Use MAY to ask for formal permission and express possibility.
Use SHOULD to give and receive advice.
Choose the right modal based on the level of formality.

Grammar Rules — All Modal Verbs

Four rules that apply to CAN, COULD, MAY, and SHOULD

Subject + MODAL + base verb (no "to")

The verb after the modal is ALWAYS in the base form — no -s, no -ing, no "to".

Rule	Correct ✅	Incorrect ❌
No -s in third person	She can swim.	She ~~cans~~ swim.
No "to" after the modal	You should rest.	You should to rest.
No -ing after the modal	He could come.	He could ~~coming~~.
Negative: modal + NOT + base verb	I cannot / can't swim.	I ~~don't~~ can swim.
Question: modal first	Can you drive?	Do you can drive?

CAN — Ability, Permission & Requests

The most common and most versatile modal verb

1 — Ability (Present)

"I can speak three languages."

"She can run 10 km without stopping."

"He cannot swim — he never learned."

Use CAN to say you have the ability to do something right now.

2 — Informal Permission (Asking & Giving)

"Can I borrow your pen?" → "Yes, you can."

"Can we go home early today?"

"You cannot use your phone in class."

Informal — fine with friends, classmates, and family. Not formal enough for a boss or authority.

3 — Informal Requests (Asking Someone to Do Something)

"Can you help me with this?"

"Can you turn down the music, please?"

"Can you pass me the salt?"

Asking others to do something for you — casual, everyday use. Adding "please" makes it more polite.

📋 CAN — Affirmative, Negative & Question Forms

✅ Affirmative: Subject + can + base verb → "I can drive."

✅ Negative: Subject + cannot / can't + base verb → "She cannot cook."

✅ Question: Can + subject + base verb? → "Can you swim?" / "Yes, I can." / "No, I cannot."

COULD — Past Ability, Polite Requests & Possibility

The past form of CAN — and a more polite way to make requests

1 — Past Ability

"When I was young, I could run very fast."

"She could speak French when she was a child."

"He could not swim until he was ten years old."

COULD = past tense of CAN for ability. Compare: "I can drive NOW" vs. "I could ride a horse AS A CHILD."

2 — Polite Requests (More Formal Than CAN)

"Could you please help me with this document?"

"Could you repeat that more slowly?"

"Could I speak with the manager, please?"

COULD is more polite than CAN for requests. Use it with strangers, in professional settings, or when you want to sound respectful.

3 — Present or Future Possibility

"It could rain this afternoon — I am not sure."

"That could be a good idea."

"We could take the bus or walk."

COULD for possibility = "maybe this is true / this is one option." It is less certain than WILL.

MAY — Formal Permission & Possibility

The formal way to ask for permission — and to express what might happen

1 — Formal Permission (Asking & Giving)

"May I come in?" → "Yes, you may." / "No, you may not."

"May I ask you a question?"

"You may use a dictionary during the exam."

MAY is more formal than CAN for permission. Use it in official, professional, or respectful contexts. Children use it to ask teachers or parents.

2 — Present or Future Possibility

"It may rain tonight — check the forecast."

"She may be late — traffic is bad."

"The exam may include vocabulary questions."

MAY for possibility is similar to MIGHT and COULD. It means "perhaps" or "there is a chance that."

📋 MAY vs CAN — Permission

"Can I use your phone?" → ✅ Informal — with a friend.

"Could I use your phone?" → ✅ Polite — with a stranger or professional.

"May I use your phone?" → ✅ Very formal — official or respectful context.

In everyday spoken English, CAN and COULD are much more common for permission. MAY sounds very formal.

SHOULD — Advice & Recommendation

Giving and asking for advice — what is the right thing to do?

1 — Giving Advice (Positive)

"You should study every day — it really helps."

"She should see a doctor if she feels sick."

"You should drink more water."

SHOULD gives a recommendation or advice — it is the right or wise thing to do, but it is not an obligation.

2 — Giving Advice (Negative)

"You should not eat so much sugar."

"He should not drive after drinking alcohol."

"You shouldn't be rude to your teachers."

SHOULD NOT / SHOULDN'T means "this is a bad idea" or "it would be wrong to do this."

3 — Asking for Advice / Expectation

"Should I call him or send an email?"

"What should we do about this problem?"

"He should be here by now — the meeting started."

SHOULD can also express expectation — something that we think is probably true or is the expected outcome.

Formality Comparison — Which Modal to Use?

Choosing the right modal based on situation and formality level

Function	Informal / Casual	Polite / Neutral	Formal / Official
Asking permission	"Can I sit here?"	"Could I sit here?"	"May I sit here?"
Asking for help (request)	"Can you help me?"	"Could you help me?"	"Would you be able to help?"
Giving advice	"You should drink water."	"I recommend you drink water."	"It is advisable to drink water."
Expressing possibility	"It could rain."	"It may rain."	"There is a possibility of rain."

Side-by-Side Comparison

All four modals across all their main uses

CAN (green)	COULD (blue)	MAY (violet)	SHOULD (amber)
Ability
"I can drive." (now)	"I could ride a bike at age five." (past)	—	—
Permission
"Can I use your pen?" (informal)	"Could I use your pen?" (polite)	"May I use your pen?" (formal)	—
Request (ask someone to do sth.)
"Can you help me?" (informal)	"Could you help me?" (polite)	—	—
Possibility
—	"It could be true." (maybe)	"It may rain." (perhaps)	—
Advice / Recommendation
—	—	—	"You should rest." / "You should not smoke."

Common Mistakes to Avoid

The most frequent modal verb errors — and how to fix them

She cans swim very well.

She can swim very well.

Rule: Modal verbs NEVER add -s in the third person. Not "cans," "coulds," "mays," or "shoulds."

You should to study more.

You should study more.

Rule: Never use "to" after a modal verb. Modal + BASE verb (no "to").

I don't can speak French.

I cannot speak French. / I can not speak French.

Rule: Modals form negatives with their own NOT — never with DON'T or DOESN'T.

Do you can help me?

Can you help me?

Rule: Modals form questions by inverting with the subject — never use DO/DOES for questions with modals.

Can I go to the bathroom? (formal exam context)

May I go to the bathroom? / Could I go to the bathroom?

Rule: In formal settings (exams, job interviews, official meetings), use MAY or COULD for permission, not CAN.

I could speak English last year. (Now I cannot.)

I could speak English last year, but now I have forgotten a lot.

Tip: COULD for past ability usually implies the ability is no longer the same or needs context. Without context it can sound odd.

You should not to eat junk food.

You should not eat junk food.

Rule: Even in negative form — modal + NOT + BASE verb. "Should not eat," NOT "should not to eat."

She may can come tomorrow.

She may come tomorrow. / She might come tomorrow.

Rule: Never stack two modals together. Use one modal only.

Audio Examples — Listen & Repeat

Practice all four modals across all their uses

🟢 CAN — Ability She can play the guitar and sing at the same time. Present ability

🟢 CAN — Request Can you please pass me the water? Informal request

🔵 COULD — Past When I was a child, I could run very fast. Past ability

🔵 COULD — Polite Could you please explain that again more slowly? Polite request

🟣 MAY — Permission May I ask you a question about your presentation? Formal permission request

🟣 MAY — Possibility It may rain tonight, so you should bring an umbrella. Possibility + advice together

🟡 SHOULD — Advice You should get more sleep — you look very tired. Giving advice

🟡 SHOULD — Asking Should I call him now or wait until tomorrow? Asking for advice / recommendation

Reading Passage

Identify CAN (green), COULD (blue), MAY (violet), and SHOULD (amber) in context

🟢 CAN 🔵 COULD 🟣 MAY 🟡 SHOULD

A New Job in Jacó

Jacó, Puntarenas, Costa Rica 🇨🇷

Marco is a young man from Jacó, a beautiful beach town on the Pacific Coast of Puntarenas. He wants to work as a surf instructor, but he is not sure where to begin. He can swim well and he can ride a surfboard, but he has never worked professionally before. His friend Luis, who already works at a surf school, has a lot of advice for him.

"You should apply at the school near the pier," Luis says. "They are looking for new instructors. But you should bring your certificate — they will want proof that you know water safety." Marco nods. He can find his certificate at home, but he should make a copy first.

The next morning, Marco arrives at the surf school early. He waits at the front desk. "May I speak with the director, please?" he asks the receptionist. "Of course. You may take a seat — she could be busy for a few minutes." Marco sits down and looks around. The school has a lot of equipment. He thinks: I could work here. This could be a great opportunity.

The director, Ana, comes out to meet him. "Can you tell me about your experience?" she asks. Marco explains that he can teach beginners and intermediate surfers. He says he can communicate in both Spanish and English, which is very useful because many tourists visit Jacó.

"You should know that this job requires early mornings," Ana explains. "We start at five thirty a.m. Could you work those hours?" Marco says yes — he can wake up early. She then asks: "May I see your safety certification?" Marco hands it over. Ana smiles. "You should come back on Friday for a trial lesson with some students. We will see how you do."

Marco leaves the school feeling excited. He calls Luis immediately. "It went well! I may get the job! She wants me back on Friday." Luis laughs and says: "That is great! You should practice your teaching before Friday. You should not be nervous — you can do this." Marco smiles and thinks: I could start my new career this week.

📖 Reading Comprehension Quiz

Answer the questions based on the reading passage above.

Grammar Practice Quiz

Test your knowledge of modal verbs — 20 questions

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