Modal verbs
Ability, permission, obligation and possibility: modal meanings and structures at a glance.
Core structure
Core modals take the base verb without to. They do not add -s for he/she/it and do not use do in questions or negatives.
| Form / use | Pattern | Example |
|---|---|---|
| Affirmative | subject + modal + base verb | She can swim. |
| Negative | subject + modal + not + base verb | She cannot swim. |
| Interrogative | modal + subject + base verb? | Can she swim? |
| Common contractions | cannot → can’t · will not → won’t | couldn’t · shouldn’t · mustn’t |
| No two core modals together | Use an alternative expression | She will be able to come. |
Can and could
Can expresses ability and permission. Could expresses general past ability, tentative possibility and polite requests.
| Form / use | Pattern | Example |
|---|---|---|
| Present ability | can + base verb | I can swim. |
| General past ability | could + base verb | I could read when I was five. |
| Permission | can + base verb | You can sit here. |
| Request | Can/Could + subject + base verb? | Could you open the window? |
| Ask permission | Could I + base verb? | Could I leave early? |
| Possible situation | could + base verb | It could rain later. |
| One successful past event | was/were able to or managed to | We managed to open the door. |
May and might
May and might express possibility, not certainty. May also gives or asks for permission in a formal style.
| Form / use | Pattern | Example |
|---|---|---|
| Possibility | may / might + base verb | She may arrive later. · It might rain. |
| Negative possibility | may not / might not + base verb | He might not come. |
| Formal permission | May I + base verb? | May I come in? |
| Give permission | may + base verb | You may leave now. |
Must
Must expresses strong obligation or a confident deduction based on evidence. Must not expresses prohibition.
| Form / use | Pattern | Example |
|---|---|---|
| Obligation | must + base verb | You must wear a seat belt. |
| Prohibition | must not + base verb | You must not park here. |
| Question | Must + subject + base verb? | Must I sign this? |
| Confident deduction | must + base verb | The lights are on. Someone must be home. |
| Negative deduction | cannot / can’t + base verb | That can’t be right. |
| Past obligation | had to + base verb | We had to leave early. |
Have to and need to
These express necessity but are not core modals: they change with the subject and use do/does/did. No obligation is different from prohibition.
| Form / use | Pattern | Example |
|---|---|---|
| Affirmative | subject + have/has to + base verb | She has to work. |
| Negative: no obligation | subject + do/does not have to + base verb | You don’t have to come. |
| Interrogative | Do/Does + subject + have to + base verb? | Does she have to work? |
| Need to | need/needs to + base verb | I need to study. |
| No necessity | don’t need to / needn’t + base verb | You needn’t wait. |
| Prohibition versus choice | mustn’t ≠ don’t have to | You mustn’t enter. / You don’t have to enter. |
Should and ought to
Use should and ought to for advice, what is right, or something expected. Ought to is followed by to, unlike core modals.
| Form / use | Pattern | Example |
|---|---|---|
| Advice | should + base verb | You should rest. |
| Negative advice | should not + base verb | You shouldn’t drive when tired. |
| Ask for advice | Should + subject + base verb? | Should I call her? |
| Alternative | ought to + base verb | You ought to apologise. |
| Expectation | should + base verb | The train should arrive soon. |
Will and would
Will expresses predictions, willingness, promises and decisions. Would expresses hypothetical results, polite requests and repeated past actions.
| Form / use | Pattern | Example |
|---|---|---|
| Prediction | will + base verb | It will rain tomorrow. |
| Decision / offer | will + base verb | I’ll help you. |
| Negative | will not / would not + base verb | She won’t come. · I wouldn’t do that. |
| Polite request | Would + subject + base verb? | Would you help me? |
| Hypothetical result | would + base verb | I would travel more if I had time. |
| Repeated past action | would + base verb | As children, we would play outside every day. |
| Polite wish | would like + to + base verb | I’d like to book a room. |
Shall
Shall is mainly used with I and we to make offers or suggestions, particularly in British English.
| Form / use | Pattern | Example |
|---|---|---|
| Offer | Shall I + base verb? | Shall I carry your bag? |
| Suggestion | Shall we + base verb? | Shall we go for a walk? |
Modal + have + past participle
Refer to past possibilities, deductions or actions that did not happen. The modal expresses the speaker’s view of the past.
| Form / use | Pattern | Example |
|---|---|---|
| Confident deduction | must have + past participle | She must have forgotten. |
| Impossible past situation | can’t/couldn’t have + past participle | He can’t have finished already. |
| Past possibility | may/might have + past participle | They might have missed the train. |
| Unused opportunity | could have + past participle | You could have called me. |
| Regret / criticism | should have + past participle | I should have studied more. |
| Criticise a past action | shouldn’t have + past participle | You shouldn’t have said that. |
| Hypothetical past result | would have + past participle | I would have helped if you had asked. |
| Unnecessary completed action | needn’t have + past participle | You needn’t have bought bread; we had plenty. |