Complete Grammar Syllabus (145 Units)

Grammar Mastery

Comprehensive reference, real-world IELTS band-boosting tips, clear structural formulas, and interactive short quizzes for intermediate to advanced English learners.

Modal Verbs of Certainty & Deduction (Must, Can't, Could)

Expressing logical deduction: must (almost 100% certain), can't (logically impossible), could/might (50% possible), and past deduction with "have + past participle".

Core Structure & Formula

Present Deduction: Subject + must / can't / could / might + Infinitive

Past Deduction: Subject + must have / can't have / could have + Past Participle

Continuous Deduction: Subject + must be / might be + verb-ing

APresent Deduction (Must vs Can't)

We use 'must' when evidence shows something is definitely true. We use 'can't' when evidence shows it is impossible.

•You've been revising for ten hours straight. You must be exhausted.

•You've just eaten a huge breakfast. You can't be hungry already!

•They only moved to this city last week. They can't know many people yet.

BPast Deduction (Must have done / Can't have done)

Reconstructing what happened in the past based on current clues.

•Ana and Tom knocked on the office door twice, but nobody answered. They must have gone to lunch.

•I can't find my USB drive. I must have left it in the computer lab.

•The candidate hasn't replied to the offer. She can't have seen the email yet.

IELTS Band 7–9 Exam Impact

Crucial for IELTS Academic Reading inferencing questions and Writing Task 2 when presenting measured, non-absolutist arguments.

Common Candidate Errors

✗ The lecture hall is empty. It mustn't be a popular course.

✓ The lecture hall is empty. It can't be a popular course.

The opposite of 'must be' for negative deduction is 'can't be' (not mustn't).

Unit 28 Interactive Short Quiz

Test your understanding with 3 verified practice exercises.

Question 1 of 3

That professor's lectures ______ excellent. The hall is always completely full.

Question 2 of 3

We knocked on our colleagues' office door, but nobody answered. They ______ .

Question 3 of 3

The candidate hasn't replied to my email. She ______ it yet.