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

What Are Modal Verbs?

Modal verbs are special "helper" verbs that add meaning to the main verb. They express things like:

• ability (can, could)
• permission (can, may)
• possibility (may, might, could)
• obligation (must, should)
• advice (should)

Important Rules

1. Modal verbs are followed by the base form of the verb (no "to"):

   • Correct: She can swim.
   • Wrong: She can to swim.

2. Modal verbs do not change for he/she/it:

   • Correct: He can play guitar.
   • Wrong: He cans play guitar.

3. To make a negative, add not after the modal:

   • She cannot (can't) come today.

4. To make a question, put the modal before the subject:

   • Can you help me?

Can

Uses:

• Ability: I can speak three languages.
• Permission (informal): Can I use your phone?
• Requests (informal): Can you open the window?

Negative: can't / cannot

I can drive, but I can't park very well.

Could

Uses:

• Past ability: When I was young, I could run very fast.
• Polite requests: Could you help me, please?
• Possibility: It could rain tomorrow.
• Suggestions: We could go to the cinema tonight.

Negative: couldn't / could not

She could play piano when she was five, but she couldn't read music.

Can vs. Could for Requests

Use could when you want to be more polite or formal.

Should

Uses:

• Advice: You should study more before the exam.
• Recommendation: You should try the pasta here -- it's excellent.
• Expectation: The train should arrive at 3:00.

Negative: shouldn't / should not

You should see a doctor about that cough. You shouldn't ignore it.

Common Phrases with Should

• "You should have..." (past advice — you didn't do it, but it was a good idea)

  You should have called me. I would have helped.

Must

Uses:

• Strong obligation: You must wear a seatbelt in the car.
• Strong certainty: She's been studying all day. She must be tired.
• Rules/laws: Passengers must show their tickets.

Negative: mustn't / must not (prohibition)

You must finish your homework. You mustn't copy from others.

Must vs. Have to

In everyday English, have to is more common. Must is more common in writing and formal rules.

May

Uses:

• Permission (formal): May I come in?
• Possibility: It may snow tonight.

Negative: may not

May I ask you a question? It may sound strange, but I need your help.

Might

Uses:

• Possibility (less certain than may): I might go to the party, but I'm not sure.
• Polite suggestion: You might want to check your spelling.

Negative: might not / mightn't

She might call you later, but she might not have time.

May vs. Might

Both express possibility, but might suggests less certainty:

• There may be a test tomorrow. (50% chance)
• There might be a test tomorrow. (30% chance)

In practice, many native speakers use them interchangeably.

Quick Reference Table

Common Mistakes

Mistake 1: Adding "to" after a modal

• Wrong: I can to speak English.
• Correct: I can speak English.

Mistake 2: Adding -s for third person

• Wrong: She musts go.
• Correct: She must go.

Mistake 3: Confusing "mustn't" and "don't have to"

• Mustn't = it is prohibited (you CANNOT do it)
• Don't have to = it is not necessary (you CAN do it, but you don't need to)

You mustn't smoke here. (It's not allowed!) You don't have to wear a suit. (It's optional.)

Mistake 4: Using "can" for formal situations

• In a job interview: Can I have a glass of water?
• Better: Could I have a glass of water? / May I have a glass of water?

Practice Tips

1. Listen for modals in movies, podcasts, and conversations. Notice which ones people use most.
2. Give advice to yourself: Practice using "should" — "I should eat more vegetables. I shouldn't stay up so late."
3. Write sentences about your abilities: "I can cook. I can't play chess. I could ride a bike when I was six."
4. Practice polite requests in real situations: at a café, in a shop, with colleagues.