B2Modals and related expressions

Speculation and deduction

Express graded certainty about present, ongoing and past situations with modal simple, continuous and perfect forms.

Overview

What this grammar does

Express graded certainty about present, ongoing and past situations with modal simple, continuous and perfect forms.

Form and rules

How it works

Use must for a strong positive deduction and can't/couldn't for a strong negative deduction.

Use may, might or could when something is possible but not certain.

Use modal + be + -ing to speculate about an activity in progress: She might be working.

Use modal + have + past participle to speculate or deduce about a completed past event: They must have forgotten.

Use modal + have been + -ing when an earlier ongoing activity matters: They must have been working all night.

A closer look

Meaning and use

Use modal + have + past participle to speculate or deduce about a completed past event: They must have forgotten.

Use modal + have been + -ing when an earlier ongoing activity matters: They must have been working all night.

Examples

See the pattern in complete sentences

She must be at work; her car isn't here.

They might be discussing the offer now.

He can't have written this; he was abroad.

You may have misunderstood the question.

They must have been working all night.

Common mistakes

What to avoid

The lights are on. Someone mustn't be inside.

The lights are on. Someone must be inside.

The evidence strongly supports a positive present deduction.

Don't call now; she must be sleeping.

Don't call now; she might be sleeping.

Might be + -ing expresses a possible activity in progress without claiming strong certainty.

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.

Previous topicPermission, obligation, prohibition and necessity Next topic Verbs of the senses