Modal Verbs: Can, Could, May, Might, Must, Should

Introduction

Modal verbs are special verbs that express ability, possibility, permission, obligation, and advice. They are followed by the base form of the main verb (without "to").

CAN — Ability and Permission

Ability: I can swim. She can speak three languages.

Permission (informal): Can I use your phone?

Requests: Can you help me?

COULD — Past Ability and Polite Requests

Past ability: I could run fast when I was young.

Polite requests: Could you open the window?

Possibility: It could rain later.

Suggestions: We could go to the cinema tonight.

MAY and MIGHT — Possibility and Permission

Possibility: It may snow tonight. She might be late.

Permission (formal): May I leave early?

:::tip

Might suggests slightly less certainty than may. "It may rain" = quite possible. "It might rain" = less certain.

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MUST — Strong Obligation and Certainty

Obligation: You must wear a seatbelt. Students must submit assignments on time.

Strong certainty: He must be tired after that long flight. (I'm sure he is.)

Prohibition (must not): You mustn't smoke in the hospital.

HAVE TO — External Obligation

Obligation: I have to work tomorrow. She has to pass this exam.

No obligation (don't have to): You don't have to come if you don't want to.

:::info

Must = internal obligation (the speaker decides). Have to = external obligation (rules, someone else decides). In practice, they are often interchangeable.

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SHOULD and OUGHT TO — Advice

Advice: You should see a doctor. You ought to apologize.

Expectation: The package should arrive tomorrow.

Comparison Table

| Modal | Main Use | Example |

|-------|---------|---------|

| can | ability/permission | I can drive. |

| could | past ability/polite | Could you help? |

| may | possibility/formal permission | It may rain. |

| might | possibility (less certain) | She might come. |

| must | obligation/certainty | You must try this. |

| have to | obligation (external) | I have to work. |

| should | advice | You should rest. |

:::exercise

Choose the correct modal verb:

You ___ (must/should) eat more vegetables for better health.

She ___ (can/could) play the piano beautifully when she was five.

Take an umbrella. It ___ (must/might) rain this afternoon.

Students ___ (must/should) wear uniforms at this school — it's a rule.

You ___ (mustn't/don't have to) bring food. We'll provide lunch.

Answers: 1. should, 2. could, 3. might, 4. must, 5. don't have to

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Summary

Modal verbs add meaning to the main verb without changing form. Learn them by function: ability, permission, possibility, obligation, and advice. Pay special attention to the difference between must and have to, and between mustn't and don't have to.