Definition / Explanation
We use modal verbs such as must, might, and can't to make logical guesses about a present situation. These forms do not show rules or permission here; they show how sure the speaker is after thinking about the evidence. Must expresses a strong conclusion, might shows possibility, and can't shows a strong negative conclusion. This grammar is common when we cannot see the full truth directly but can infer it. The meaning comes from logic, not from certainty based on direct knowledge.
Key Rules
- Use must + base verb for a strong positive deduction: She must be at work.
- Use might / may / could + base verb for a possible explanation: He might be busy.
- Use can't + base verb for a strong negative deduction: That can't be true.
- This use is about now or a general present situation.
- Do not confuse deduction with permission: You may leave now has a different meaning.
Examples
- She must be at work. Her car is outside.
- He can't be serious.
- They might know the answer.
- This could be the right address.
- You must feel tired after that trip.
Common Mistakes
- ❌ She must to be at work. -> ✅ She must be at work.
- ❌ He can't is serious. -> ✅ He can't be serious.
- ❌ They maybe know the answer. -> ✅ They might know the answer.