How modal verbs work
No -s with he, she, it
She can speak French.
not “she cans”
The next verb has no to
You should see a doctor.
not “should to see”
No do in questions and negatives
May I come in?
You shouldn’t eat so much sugar.
Have to, need to and be able to are not true modals: they change (she has to) and need do in questions (Do you have to…?). But they have all tenses: I had to work, I’ll be able to come.
English modal verbs: table of meanings
| Modal | Meaning | Example |
|---|---|---|
| can | ability, possibility, permission | I can drive. Can I sit here? |
| could | past ability, polite request, possibility | I could swim at five. Could you help me? |
| may | formal permission, possibility | May I ask a question? It may rain. |
| might | weaker possibility | I might come later. |
| must | obligation (from the speaker), certainty | I must call mum. She must be tired. |
| have to | obligation from rules or circumstances | I have to wear a uniform. |
| mustn’t | prohibition | You mustn’t smoke here. |
| don’t have to | no obligation | You don’t have to come. |
| should / ought to | advice | You should rest. |
| would | polite request, imaginary situation | Would you like tea? |
| shall | offers with I / we | Shall I open the window? |
Must or have to? Mustn’t or don’t have to?
In the positive the difference is small: must is an obligation the speaker feels, have to comes from rules and circumstances. But in the negative the meanings are opposite!
| Form | Meaning | Example |
|---|---|---|
| mustn’t | it’s not allowed | You mustn’t park here. |
| don’t have to | it’s not necessary | You don’t have to pay — it’s free. |
How sure are you? must, may, might, can’t
| Certainty | Example |
|---|---|
| ~ 95% | She must be at home — the lights are on. |
| ~ 50% | She may / might / could be at home. |
| ~ 5% | She can’t be at home — I saw her at work. |
Modals about the past: modal + have + V3
You should have told me.
criticism or regret
He must have forgotten.
They might have missed the train.
She can’t have said that.
I could have won, but I fell.
Passive modals: modal + be + V3 — The form must be signed. More in the passive voice.
Common mistakes
What learners of English often say. On the left — the mistake, on the right — the correct version.
Wrong:
She cans swim.Right: She can swim.
Modals never take -s.
Wrong:
You should to see a doctor.Right: You should see a doctor.
No to after should, can, must.
Wrong:
Do you can help me?Right: Can you help me?
Modals don’t take do.
Wrong:
I must to go.Right: I must go. / I have to go.
Must without to, have to with to.
Wrong:
You mustn’t come, it’s optional.Right: You don’t have to come, it’s optional.
Mustn’t is a ban; don’t have to means optional.
Wrong:
I musted work yesterday.Right: I had to work yesterday.
Must has no past: use had to.
Check yourself
Quiz: Modal verbs
12 questions with an explanation after every answer. Free, no sign-up.
can · must · should · might