Must, might, can’t: present deduction
Draw conclusions about the present from evidence: must be, might be, could be, can’t be — including continuous forms.
In this lesson you will
- Use must/can’t for strong deductions
- Use might/may/could for possibility
- Use continuous forms for actions happening now
Learn
must = I’m sure it’s true: The lights are on — they must be* home.* can’t / couldn’t = I’m sure it’s not true: She can’t be* 40 — she looks 25.* (Not mustn’t for deduction.)
might / may / could = it’s possible: He might be* stuck in traffic.* might not / may not = possibly not. (couldn’t = impossible, not possibly not.)
Continuous: modal + be + -ing for actions in progress now: She isn’t answering — she must be driving.
Support deductions with evidence: Judging by…, Considering that…, Given that…
Examples
- There’s no answer. They must be on holiday.
- That can’t be the right address — it’s a car park.
- He might be working late tonight.
- Given how quiet it is, the shop may be closed.
Vocabulary
deduction
a conclusion from evidence
evidence
facts that show something
judging by
based on
stuck
unable to move
given that
considering that
Practice
You’ve been travelling all day. You ___ be exhausted.
Speaking
Look around you or at five photos and make deductions: Who might this person be? What must be happening? Where can’t this be?
Writing
Write about a mysterious situation (100–120 words) using present deduction modals and evidence phrases.
Lesson quiz
She’s smiling. She ___ have good news.
Review
Key points
- must = sure true; can’t/couldn’t = sure false.
- might/may/could = possible.
- modal + be + -ing for now.
- Evidence: judging by, given that.
What you learned
- ✓ I can make present deductions.
- ✓ I avoid mustn’t for deduction.
- ✓ I can support conclusions.
Grammar reference: Modals of deduction: must, might, can’t