Intermediate 📐 Grammar · #119 of 305

Modal Verbs of Deduction (Present)

must, can't, might for logical conclusions.

Examples

  • He must be tired.
  • That can't be true.

Key rules

  • Must = sure it is true
  • Can't = sure it is not true
  • May/might/could = possible
  • Do not use mustn't for deduction, use can't

Common mistakes

  • He mustn't be at home, his car is gone → He can't be at home, his car is gone
  • She can be late → She might be late
💡 Tip: Use can't, not mustn't, for negative certainty.
Practise this topic in the appPractise Intermediate quiz
← Make, Let, AllowModal Verbs of Deduction (Past) →

Related Intermediate topics

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Present Perfect Continuous

have been + -ing stresses duration up to now.

Past Perfect

had + past participle for an earlier past action.

Past Perfect Continuous

had been + -ing for duration before a past moment.

Future Continuous

will be + -ing for actions in progress at a future time.

Future Perfect

will have + past participle for completion before a future time.

Future Perfect Continuous

will have been + -ing for duration up to a future point.