Modal Verbs: Must, Might, May, Have To— B1 Grammar Exercises
Published March 14, 2026
Exercise 1 — Multiple Choice
You ____ finish your homework before going out; it is very important.
She ____ come to the party if she feels better, but she is not sure yet.
You ____ wear a helmet when riding a bike; it is the law.
They ____ go to the concert, but they have not decided yet.
You ____ be quiet in the library.
He ____ finish the report by tomorrow; the boss said it is urgent.
We ____ see a movie this weekend, but we are not sure yet.
Take your umbrella; it ____ rain later.
She ____ help us with the project, but she is very busy.
You ____ not smoke in this area; it is strictly forbidden.
Your friend looks pale and hasn't eaten all day. You say: She must be hungry. Your boss tells you the deadline is Friday. You think: I have to finish this by Friday. You hear thunder outside. You say: It might rain later. Three different modals, three different jobs — certainty, obligation, and possibility. The difficulty is knowing which one fits the situation.
Modal verbs change the meaning of the main verb without changing its form. After must, might, and may, you always use the base form of the verb (the infinitive without to). Have to works differently — it is not a true modal, but it fills a gap that must cannot cover.
Form
| must | might / may | have to | |
|---|---|---|---|
| Positive | You must wear a helmet. | She might arrive late. | They have to wait outside. |
| Negative | You must not park here. | He might not come tonight. | We don't have to pay today. |
| Question | rare — see note below | uncommon | Do I have to sign this? |
Notice that must, might, and may have no -s form. You say she must, never she musts. Have to behaves like a normal verb — it changes to has to in the third person and needs do/does for questions and negatives.
Must — Obligation and Strong Belief
Obligation (rules and strong personal necessity)
Must expresses obligation that comes from the speaker — a rule you set, a strong personal feeling, or an authority making a direct statement.
- All passengers must fasten their seatbelts during take-off.
- I must call my mother — it's her birthday.
Strong belief (logical deduction)
When you are almost certain something is true based on evidence, use must. You don't have proof, but the evidence makes it the only logical conclusion.
- Tom has been working since 6 a.m. He must be exhausted.
- The restaurant is completely empty. The food must not be very good.
Have To — External Obligation
Have to describes obligation that comes from outside — rules, laws, someone else's requirements, or circumstances you cannot control. This is the key difference from must, which is more personal.
- We have to wear a uniform at work. (the company requires it)
- Maria has to renew her visa before September. (the law requires it)
In everyday conversation, must and have to often overlap for obligation. The distinction matters more in writing and formal contexts. But there is one place where the difference is critical — the negative.
Must Not vs Don't Have To
must not = it is prohibited (don't do this)
You must not use your phone during the exam. (it's forbidden)
don't have to = it is not necessary (you can if you want)
You don't have to wear a tie — it's a casual office. (it's your choice)
Mixing these up changes the meaning completely. You must not come to the party means you are banned. You don't have to come to the party means it's optional.
Might and May — Possibility
Might and may both express that something is possible but not certain. In most everyday situations, they are interchangeable.
- The meeting might take longer than expected.
- We may need extra chairs for the event.
May is slightly more formal than might. In spoken English, might is far more common. In written or professional English, may appears more often.
May for permission (formal)
May has a second use: formal permission. This overlaps with can and could, but may is more polite and more formal.
- May I borrow your pen? (formal / polite)
- Students may leave after the bell. (official permission)
Might not vs may not
Both mean "it is possible that… not." Neither means prohibition.
- She might not pass the test — she hasn't studied much.
- The delivery may not arrive before Friday.
The Certainty Scale
These modals sit on a scale from most certain to least certain:
| Level of certainty | Modal | Example |
|---|---|---|
| Almost certain | must | She's not answering. She must be asleep. |
| Possible | may | He may know the answer — ask him. |
| Possible (slightly less sure) | might | I might go to the gym later. I'm not sure yet. |
| Impossible / prohibited | can't | That can't be right — the numbers don't add up. |
For more on using modals to express deduction and speculation, see speculation and deduction with modal verbs at B2.
Past Forms
Must, might, and may have no past tense. To talk about the past, you need different structures:
| Present | Past equivalent |
|---|---|
| must (obligation) | had to — I had to work late yesterday. |
| must (deduction) | must have + past participle — She must have forgotten. |
| might / may (possibility) | might have / may have + past participle — They might have missed the train. |
These past modal forms are covered in detail at advanced modal verbs (C1).
Common Mistakes
| Wrong | Correct | Why |
|---|---|---|
| She musts go now. | She must go now. | Modal verbs never take -s. |
| I must to finish this report. | I must finish this report. | After true modals, use the base verb — no to. |
| You don't must park here. | You must not park here. | Must makes its own negative: must not. No do/does. |
| You mustn't pay — it's free. | You don't have to pay — it's free. | Mustn't = prohibited. Don't have to = not necessary. |
| I think it must rain later. | I think it might rain later. | Must = almost certain. For a guess, use might or may. |
| She might to come tomorrow. | She might come tomorrow. | Same rule: no to after a modal verb. |
| Do you must work on Saturday? | Do you have to work on Saturday? | Use have to for questions about obligation. |
Quick Summary
Must — strong obligation (from the speaker) or strong belief based on evidence.
Have to — obligation from outside (rules, laws, other people). Use it for questions and past tense.
Must not — prohibited. Don't have to — not necessary. Never confuse them.
Might / May — something is possible but not certain. May is slightly more formal.
May (in questions) — formal permission: May I sit here?
Related Topics
If you are starting with modals, review can, could, and should at A2 first. For using modals to make deductions about the present and past, see speculation and deduction with modal verbs. For advanced uses including must have, can't have, and needn't have, see advanced modal verbs.
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