Modal Verbs
Modal verbs — can, could, may, might, must, should, will, would, shall — add meaning to the main verb, expressing ability, possibility, permission, obligation, and more.
What are modal verbs?
Modal verbs are a type of auxiliary verb. They always appear before the base form of the main verb and never change their form — no -s in the third person, no -ing, no infinitive with to.
The core modals are: can, could, may, might, must, shall, should, will, would. Semi-modals (have to, need to, ought to, used to) behave similarly but follow different grammar rules.
Key properties of modal verbs
- Always followed by the base form of the verb (no to): She can swim. He must leave.
- No -s in the third person singular: He can ✓ / He cans ✗
- Form negatives by adding not: cannot / can't, should not / shouldn't
- Form questions by inversion: Can she swim? Must he go?
The main modals and their meanings
| Modal | Main uses | Example |
|---|---|---|
| can | Ability; informal permission | She can speak three languages. Can I sit here? |
| could | Past ability; polite request; possibility | He could run fast as a child. Could you help me? |
| may | Formal permission; possibility | You may leave now. It may rain later. |
| might | Weaker possibility | She might be at home. I might go — not sure. |
| must | Strong obligation; logical deduction | You must wear a seatbelt. He must be tired. |
| mustn't | Prohibition | You mustn't smoke in here. |
| shall | Offers and suggestions (I/we); formal future | Shall I open the window? We shall return. |
| should | Advice; expectation | You should see a doctor. The parcel should arrive today. |
| will | Future; willingness; prediction | She will call you later. I'll carry that for you. |
| would | Polite request; hypothetical; past habit | Would you mind? I would love to go. We would play here as kids. |
Ability: can / could / be able to
She can play the piano. (present ability)
He could swim when he was five. (past ability)
I wasn't able to finish in time. (past — negative)
Possibility and deduction: may / might / must / can't
It may snow tonight. (possibility — maybe 50%)
She might be in a meeting. (weaker possibility — maybe 30%)
He must be exhausted — he worked all night. (logical deduction — certain)
That can't be right. (logical deduction — impossible)
Obligation and advice: must / have to / should
| Modal | Meaning | Example |
|---|---|---|
| must | Strong internal obligation | I must call my mother — it's been weeks. |
| have to | External obligation (rule or requirement) | You have to show ID to enter. |
| should / ought to | Advice or recommendation | You should drink more water. |
| don't have to | No obligation (optional) | You don't have to come if you're tired. |
| mustn't | Prohibition | You mustn't park here. |
Requests and offers: can / could / will / would / shall
Can you pass the salt? (informal request)
Could you help me, please? (polite request)
Would you mind closing the door? (very polite)
Shall I make some tea? (offer — British English)
Will you join us for dinner? (invitation)
Don't confuse must and have to negatives: mustn't = prohibition (you are not allowed); don't have to = no obligation (it's optional). "You mustn't leave" ≠ "You don't have to leave."
Tip: Modal verbs never take -s, -ed, or -ing. If you need a past or future form, use a semi-modal instead: was able to (past of can), will have to (future of must).