Grammar Made Simple

Modal Verbs

The verbs that express ability, permission, obligation, possibility and more.

Ability: "You can do this." · Obligation: "You must try."
Possibility: "It might rain." · Advice: "You should rest."

What Are Modal Verbs?

Modal verbs are a special group of auxiliary (helping) verbs. They work differently from regular verbs.

Modal verbs are used before a base verb to add meaning about ability, permission, obligation, deduction, possibility or advice. The modal changes the attitude of the sentence — how certain, how necessary, or how permitted something is.

Key rules — modals behave differently from other verbs:

Always followed by a bare infinitive (no "to"): She can swim ✓ She can to swim ✗
No -s in third person singular: He must go ✓ He musts go ✗
Negatives: add not directly: cannot / can't, must not / mustn't, should not / shouldn't
Questions: invert the modal and subject: Can she drive? Must we leave?
No infinitive, -ing or past participle form — use alternatives when needed: be able to, have to, be allowed to

💡 Think of modal verbs as dials on an attitude control panel. The base verb says what happens; the modal tells you how certain, how necessary or how permitted it is.

Exercise 1

Click the Modal Verb Phrase

Read the task, then click all the words that form the modal verb phrase.

Sentence 1 of 5

🎯 Click the modal verb phrase that expresses deduction (logical conclusion).

Click all the words in the modal verb phrase.

Sentence 2 of 5

🎯 Click the modal verb phrase that expresses past regret.

Click all the words in the modal verb phrase.

Sentence 3 of 5

🎯 Click the modal verb phrase that shows something is not necessary.

Click all the words in the modal verb phrase.

Sentence 4 of 5

🎯 Click the modal verb phrase that expresses possibility (something that might happen).

Click all the words in the modal verb phrase.

Sentence 5 of 5

🎯 Click the modal verb phrase that expresses past ability.

Click all the words in the modal verb phrase.

The Six Functions

Each modal verb can express one or more functions. The same modal can mean different things in different contexts — context is key.

Ability

What someone is able to do — present, past or future.

Permission

Asking for or giving permission — or saying what is allowed.

Obligation & Necessity

What is required, necessary or forbidden.

⚠️ mustn't vs don't have to — very different meanings!

= it is forbidden: "You mustn't tell anyone." (Do not do it!)

= it is not necessary: "You don't have to come." (You can choose.)

Deduction & Certainty

Expressing how certain you are about something — reasoning from evidence.

Possibility & Probability

How likely something is to happen — in the present or future.

Advice & Recommendation

Suggesting what someone ought to do — from gentle to strong.

🔑 The certainty scale (deduction):
must → very certain | should → expected | may → possible | might / could → less certain | can't → impossible

Exercise 2

Identify the Function

What function does the modal verb have in each sentence?

Question 1 of 6

"You must wear a seatbelt at all times."

Question 2 of 6

"She must be exhausted — she's been working since 6am."

Question 3 of 6

"It might snow later — bring a warm coat."

Question 4 of 6

"You don't have to come to the meeting if you're busy."

Question 5 of 6

"You should have called before coming — she wasn't home."

Question 6 of 6

"That can't be right — I checked the figures myself."

Exercise 3

Choose the Right Modal

Choose the modal that best fits the meaning described.

Question 1 of 5

You want to say it is forbidden to use a phone in the exam room.

Question 2 of 5

You want to make a polite request for someone to open the window.

Question 3 of 5

You are fairly certain that the keys are in your bag — you put them there this morning.

Question 4 of 5

You want to express strong regret that you didn't study for the exam.

Question 5 of 5

You want to say that when you were a child, you were able to swim across the lake.

Exercise 4

Mixed Review

A mix of everything — ability, permission, obligation, deduction, possibility, and advice.

Ability & Permission

Question 1 of 16

She ___ speak four languages fluently. (present ability)

Question 2 of 16

When he was a child, he ___ climb trees easily. (past ability)

Question 3 of 16

___ I use your phone for a minute? (formal permission)

Question 4 of 16

You ___ park here — it's a private driveway. (refusing permission)

Obligation & Prohibition

Question 5 of 16

All passengers ___ fasten their seatbelts. (a rule)

Question 6 of 16

You ___ smoke inside the building. (forbidden)

Question 7 of 16

You ___ come to the party if you don't want to. (not necessary, your choice)

Question 8 of 16

I ___ wear a uniform at my job. (an external rule)

Deduction & Possibility

Question 9 of 16

She's not answering her phone. She ___ be busy. (a logical conclusion)

Question 10 of 16

It ___ rain later, but I'm not sure. (possibility, not certain)

Question 11 of 16

He ___ be at work — I just saw him at the beach. (certain negative deduction)

Question 12 of 16

There's a light on. Someone ___ be home. (a logical conclusion from evidence)

Advice & Past Modals

Question 13 of 16

You ___ see a doctor about that cough. (advice)

Question 14 of 16

I ___ have studied harder for that exam. (past regret)

Question 15 of 16

She ___ have taken the earlier train — she missed her connection. (criticism of a past mistake)

Question 16 of 16

When I was younger, I ___ swim across the lake. (past ability)

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You completed all the exercises.