Everything you need to use modal verbs correctly: the formula, when to use it, signal words, common mistakes and exercises with answers.
Modal verbs express ability, permission, obligation, advice and prediction. Affirmative: S + modal + V (bare infinitive); Negative: S + modal + not + V; Interrogative: Modal + S + V? Signal words: can / could (ability), may / might (possibility), must (obligation), should / ought to (advice), will / would (willingness, offers), shall (offers and suggestions).
| Form | Structure | Example |
|---|---|---|
| Affirmative | S + modal + V (bare infinitive) Modals do not change with the person: He can swim (NOT: He cans swim) | She can speak three languages. The modals: can, could, may, might, shall, should, will, would, must |
| Negative | S + modal + not + V cannot (one word), mustn't, shouldn't, won't, couldn't | You must not park here. can not is written as one word, cannot, and contracts to can't |
| Interrogative | Modal + S + V? Can you...? / Should I...? / May I...? | Can you help me with this? Short answers: Yes, I can. / No, I can't. |
can/could say that someone is able to do something
can/could/may are used to ask permission
must/have to express something you are obliged to do
should/ought to are used to give advice
may/might/could express something that may happen
| Word | Example | Note |
|---|---|---|
| can | I can swim very fast. | Expresses ability in the present |
| could | She could read when she was four. | A past ability, or a polite way of putting it |
| may | May I use your phone? | Asking permission politely, or saying something is possible |
| might | It might rain tomorrow. | Less likely than 'may' |
| must | You must wear a seatbelt. | An obligation you feel yourself, or a confident deduction |
| should | You should see a doctor. | Advice and suggestions |
Fill in the blank, then open the answer to check it.
Options: can · might · must · would
must. 'must' expresses obligation, and wearing a seatbelt is a legal requirement.
Options: can · could · must · should
could. 'could' expresses an ability in the past.
Options: can · must · should · would
should. 'should' is used to give advice.
Options: May · Must · Shall · Will
May. 'May I...?' is a polite way of asking permission.
Options: can · might · must · will
might. 'might' says something is possible but not certain.
Options: can't · don't have to · mustn't · shouldn't
mustn't. 'mustn't' means it is forbidden. 'don't have to' means it is simply not necessary - a different thing entirely.
Options: can't · don't have to · mustn't · shouldn't
don't have to. 'don't have to' means there is no obligation.
Options: Could · Might · Must · Shall
Could. 'Could you...?' is a polite way of asking someone to do something.
Options: can · could · might · must
can. 'can' expresses a present ability.
Options: may · must · should · would
should. 'should' is used to advise what someone ought to do.
Options: can · might · must · should
must. 'must' draws a confident conclusion from the evidence.
Options: don't have to · mustn't · shouldn't · won't
mustn't. 'mustn't' means forbidden, and a live wire is dangerous, so it is a prohibition.
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