Grammar › Modal Verbs
Modal Verbs
Quick answer
Modal verbs add meaning to a main verb. The main groups are:
- Ability — can, could, be able to (She can swim).
- Obligation — must, have to (You must stop).
- Advice — should, ought to (You should rest).
- Possibility — may, might, could (It may rain).
Modals never change form (she can, he must) and are followed by the base verb. For the past, use a modal perfect: modal + have + past participle.
| Modal group | Use it for | Example |
|---|---|---|
| Can, Could & Be able to | Ability and possibility | She can swim. Could you help? |
| Must & Have to | Obligation and necessity | You must stop. I have to work. |
| Should & Ought to | Advice and recommendations | You should rest. |
| May, Might & Could | Possibility and probability | It may rain later. |
| Modal Perfects | Guessing and regret about the past | She must have left. I should have called. |
Which modal?
- Talking about ability? → can, could, be able to (She can drive).
- Talking about obligation or rules? → must, have to (You must wear a helmet).
- Giving advice? → should, ought to (You should see a doctor).
- Talking about possibility? → may, might, could (It might snow).
- Guessing or regretting the past? → modal perfects (She must have left).
Related grammar points
- Must vs Have to — Personal obligation or external rule?
- Can't vs Mustn't — Impossibility or prohibition?
- Permission: Can, Could & May — Asking and giving permission
- Requests, Offers & Suggestions — Could you…? Shall I…? Why don’t we…?
- Would rather & Would prefer — Talking about preferences
- Need & Needn't — Necessity, and needn’t have vs didn’t need to
- Deduction: must, might & can't — How sure you are (present)
Frequently asked questions
What are modal verbs?
Helper verbs like can, could, must, should, may, might and will that add meaning — ability, obligation, possibility, advice — to a main verb. They are followed by the base verb (can swim, must go).
Do modal verbs change with he/she/it?
No. Modals have one form for every subject: she can, he must, it might — never "she cans" or "he musts".
What comes after a modal verb?
The base verb with no "to": you should rest, they might come. The exceptions are "ought to" and "have to", which keep "to".
How do I talk about the past with modals?
Use a modal perfect: modal + have + past participle (She must have left; I should have called).