Modal verbs

Grammar for

Modal Verbs

Permission, prohibition, obligation and ability and advice

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Summary

Permission I

· – – – –

Permission II

– – – · ·

Obligation II

– – – –

Obligation I

· · – – –

Advice

· – – – –

– – – – –

Prohibition

· · · – –

Permission I

Can, could, may, might

The most common modal verbs to talk about permission are can, could, may and might.

• Can I sit here? (informal; asking for permission)
• You can/can’t sit here.
• Could I use this chair? (more polite)
• You may use this chair. (formal; giving permission)
• Might/May I use this chair? (more formal; asking for permission)
• Sorry, you can’t use this chair. (informal; refusing permission)
• Sorry, you may not use this chair. (formal; refusing permission)

Permission II

Was/were allowed to, couldn’t

To talk about the past, we use the forms was/were allowed to or couldn’t.

• He wasn’t allowed to sit down during the lesson.
• He couldn’t sit down during the lesson.
• He was allowed to receive visits. (NOT could)

OBLIGATION I

Must / have to

Must and have to are used to express obligation. When we use must this usually means that the obligation comes from the speaker, it’s like a personal obligation, whereas have to normally means that the obligation is external.

• I must give up smoking. (I need to, I say so)
• I have to give up smoking. (I’m obliged. My doctor says so)

In informal English can also use ‘ve got to to express obligation (⇒ See Have – auxiliary or main verb).

• I’ve got to be there before ten.

In the past, we use had to in every instance.

• I had to give up smoking. (because I needed to, or because my doctor forced me to).

OBLIGATION II

Mustn’t / don’t have to

The negative forms mustn’t and don’t have to are completely different. Mustn’t is used to express prohibition (an obligation not to do something), whereas don’t have to is used to express an absence of obligation. (⇒ See Have to, must, should – obligation, prohibition, necessity, advice)

• You mustn’t reveal where you get the information. (=you have the obligation not to do it)

• You don’t have to arrive before 7. (=you can do it, but it’s not necessary, there’s no obligation)

PROHIBITION

Can't / Mustn't

Can't' and 'mustn't' (must not) are used to show that something is prohibited (not allowed)

• You can't go into that restaurant without a tie.
• You can't drive in this country unless you are over eighteen.
• You mustn't use your phone in class.

Can't' usually gives the idea of something that is against the rules. Mustn’t usually means that it is the speaker who is setting the rule.

4 ADVICE

English speakers use the modal verbs “should,” “ought to” and “had better” to express that they think something is a good (or a bad) idea. “Should” is the most common way to give advice. We use had better + infinitive (without to) to talk about actions we think someone should or shouldn’t do. There is often a negative result if the action is carried out.

• Young children shouldn't watch violent TV shows.
• It's really cold outside. You ought to wear a warm jacket.
• You had better not forget to pay your tuition. If you do, the university will kick you out!

You should be ready to modal

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