All English 4U

English Grammar in Use · Murphy

Intermediate Grammar

Master English grammar one unit at a time. Clear notes, then 40+ interactive exercises with instant feedback — based on the topics in English Grammar in Use (Intermediate).

Continuous or simple?

Present perfect cont.

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UNIT 10

Perfect: cont. or simple?

Future: present tenses

Future: will / going to

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UNIT 24

Future cont. & perfect

UNIT 28 · Intermediate · B1–B2

Must and can’t“must be / can’t be · must have done / can’t have done” — 44 interactive questions

Correct answers

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📖 Grammar Reference — Must and can’t

Study the notes, then work through the six exercises.

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What you’ll learnmust = I’m sure it’s true · can’t = I’m sure it’s not true

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~15 minNotes + 6 exercises

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44 questionsInstant feedback

A must — I’m sure it’s true (now)

She must be tired

Use must + base verb when you look at the evidence and feel sure something is true. You are not stating a fact — you are making a confident guess (a deduction).

must be	You’ve worked all day. You must be exhausted.
must be doing	The light’s on, so she must be working late.
must + verb	He speaks four languages — he must have a good ear.

💡 After must use the base verb — never to: (not must to be).

B can’t — I’m sure it’s NOT true (now)

The opposite of must is can’t (not mustn’t). Use can’t when you feel sure something is impossible or untrue.

sure → trueThey’ve been driving for hours. They must be tired.

sure → not trueThey’ve only just met — they can’t be married! (not mustn’t)

impossible nowThat can’t be Tom — Tom is much taller.

C must have (done) — I’m sure it happened

I must have left it

For a sure guess about the past, use must have + past participle. You are sure something happened, because of what you can see now.

evidence now The keys aren’t here — I must have left them at work.

past state She knew everyone’s name; she must have been there before.

obvious cause The grass is wet, so it must have rained.

💡 Say must have, never must of. They sound the same in speech, but of is wrong in writing.

D can’t have (done) — I’m sure it didn’t happen

For a sure guess that something did not happen, use can’t have (or couldn’t have) + past participle.

sure it happened → must havesure it didn’t → can’t / couldn’t have

impossible He can’t have heard me — he didn’t even look up.

also OK They couldn’t have caught the train; they left too late.

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Remember — must = I’m sure it’s true · can’t = I’m sure it’s not true (now) · must have (done) = I’m sure it happened · can’t / couldn’t have (done) = I’m sure it didn’t. The opposite of must here is can’t, not mustn’t. Write must have, never must of.

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Original practice material inspired by the English Grammar in Use syllabus (Cambridge University Press). Example sentences and exercises are written by All English 4U.