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B2 Pre-advanced
B2 grammar contents
B2Modals and related expressions

Permission, obligation, prohibition and necessity

Choose modal and semi-modal forms according to strength, source of obligation, time reference and whether something is required, optional or forbidden.

Overview

What this grammar does

Choose modal and semi-modal forms according to strength, source of obligation, time reference and whether something is required, optional or forbidden.

Form and rules

How it works

1

Must/have to can express necessity; must often sounds speaker-imposed or strongly stated, while have to readily describes external rules and works across tenses.

2

Mustn't means prohibition; don't have to/needn't means lack of necessity, not prohibition.

3

Should/ought to express advice or weaker obligation; be supposed to expresses expectation, arrangement or rule.

4

Permission can use can, could or may depending on context/formality; be allowed to is useful across tenses.

5

Past/future meanings often require had to, was allowed to, will have to or will be allowed to rather than a simple modal form.

A closer look

Meaning and use

Permission can use can, could or may depending on context/formality; be allowed to is useful across tenses.

Past/future meanings often require had to, was allowed to, will have to or will be allowed to rather than a simple modal form.

Examples

See the pattern in complete sentences

Employees have to wear identification.

You mustn't copy confidential data.

You needn't attend both sessions.

We're supposed to submit expenses by Friday.

Visitors aren't allowed to enter this area.

Common mistakes

What to avoid

You needn't use your phone during the exam; it's forbidden.
You mustn't use your phone during the exam; it's forbidden.

Mustn't expresses prohibition.

The jacket is optional, so you mustn't wear it.
The jacket is optional, so you don't have to wear it.

Lack of necessity means the action is optional.

Ready to practise?

The test combines multiple choice, gap completion, error correction, and sentence building so students have to recognise and produce the grammar, not simply reread the rule.

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