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.

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.

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

SHOULD and OUGHT TO — Advice

• Advice: You should see a doctor. You ought to apologize.
• Expectation: The package should arrive tomorrow.

Comparison Table

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.