01 Present deduction
Degrees of certainty
1must + base verb
Certainty
- 95–100% sure it is true
Example
- They must be tired after walking all day in the heat.
2may / could + base verb
Certainty
- about 50% possibility
Example
- The waves may be stronger than before.
3might + base verb
Certainty
- about 30% possibility
Example
- The fishermen might need to change their methods.
4can't + base verb
Certainty
- 95–100% sure it is NOT true
Example
- This can't be the right place; the map shows we are far away.
How to read the evidence
- Positive evidence that makes you almost certain → must.
- Evidence against the idea → can't, not mustn't. Mustn't means prohibition, not deduction.
- A possibility you cannot confirm → may / could / might; might is weaker than may in exam keys.
- Sentences from the unit: "The risks can't be completely avoided, but they can be reduced." / "Families should take precautions during storms."
Quick check
- She … be at home; her lights are off. → can't
- They … be tired after walking all day in the heat. → must
- This … be the right place; the map shows we're still far away. → can't