Unit 3 - Mystery
Perfect Modal Verbs (Deduction)
Judge past situations using modal verbs that show degrees of certainty.
1. Starting Point
B1 logical conclusion: He must be tired after such a long day.
Deduction about the past: He must have been tired after such a long day.
2. Degrees of Certainty
| Certainty | Modal | Example |
|---|---|---|
| High | must have | She must have left early; her desk is empty. |
| Medium | may/might have | They might have misunderstood the instructions. |
| Low | could have | The error could have occurred during export. |
| Negative | can’t/couldn’t have | He can’t have finished already—he arrived late. |
3. Form
Modal + have + past participle
- Positive: The documents must have been signed.
- Negative: The documents can’t have been signed yet.
4. Evidence Language
- Use phrases like Apparently, Evidently, It seems that to introduce deductions.
- Combine with adverbs: She clearly must have known about the change.
Stay logical
Match your modal to the evidence you actually have. Don’t use must have unless evidence is strong.
5. Practice
- Write a short detective summary using all four certainty levels.
- Rewrite simple past statements as deductions with varying confidence.
- Listen to a news report and note which modal deductions you could make.
Quick Review
- Deductions judge how sure you are about past events.
- Must have (almost certain), may/might/could have (less certain), can’t/couldn’t have (almost impossible).
- Keep the form modal + have + V3 consistent.