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Modals of Deduction

Modals of deduction are used to make guesses or conclusions based on the information we have.

B2Verbs & Verb Patterns

What are Modals of Deduction?

Modals of deduction are a way to express our guesses or conclusions based on the information we have.

  • must is used to show we are very sure about something, like when we see clues that make us think something is true.
  • can't is used to show we are very sure something is not true, like when we see clues that make us think something is impossible.
  • may, might, and could are used to show we are not very sure, like when we have some clues but not enough to be certain.

When to Use Modals of Deduction

  • We use modals of deduction when we want to make an educated guess based on the information we have.
  • We use modals of deduction to show the degree of our certainty, from very sure to not very sure.
  • We use modals of deduction to avoid stating something as a fact when we are not completely sure.

Example Sentences

  • The door is locked, so she must have left the house.
  • The door is open, so she can't have left the house.
  • The door is locked, but the window is open, so she may have gone out the window.
  • The door is locked, but the window is open, so she might have gone out the window.
  • The door is locked, but the window is open, so she could have gone out the window.
  • The door is locked, and the window is closed, so she can't have gone out.

Common Mistakes

  • Wrong: The door is locked, so she going out. Correct: The door is locked, so she must have gone out.
  • Wrong: The door is open, so she not leave the house. Correct: The door is open, so she can't have left the house.

Memory Trick

One way to remember how to use modals of deduction is to think of a scale of certainty, from very sure to not very sure, and use the modal that matches your degree of certainty.

Quick check
Which modals of deduction can be used to express a possibility or logical conclusion?

Where this matters in your exam

In IELTS, modals of deduction are assessed in Writing Task 2 and Speaking Part 3, where you need to make logical conclusions and express degrees of certainty.

  • Writing Task 2

    Use modals of deduction to present a clear opinion and support it with logical arguments.

  • Speaking Part 3

    Use modals of deduction to discuss and make conclusions about a topic with the examiner.