Modals of deduction

Rules

• Rule 1: must = I'm sure it's true

  When a clue makes us sure something is true, use must + verb.

  Pattern: subject + must + verb

  Example: You've been cycling for hours. You must be thirsty.

  Example: Kerem reads a book every week. He must love stories.

• Rule 2: can't = I'm sure it's not true

  When something seems impossible, use can't + verb. Careful: mustn't usually means “not allowed”. (In American English *must not* is also used for a weaker negative guess: *He must not be home.* But for “impossible”, use can't.)

  Pattern: subject + can't + verb

  Example: He can't be asleep. I can hear him singing.

  Example: This can't be the right road. It ends at a river!

• Rule 3: might / may / could = maybe

  When we're not sure, use might, may or could + verb.

  Pattern: subject + might / may / could + verb

  Example: Where's Elif? She might be in the art room.

  Example: Take an umbrella. It could rain this afternoon.

• Rule 4: Modal + base verb

  No to and no -s after a modal. For something happening right now, use modal + be + -ing.

  Pattern: modal + verb · modal + be + -ing

  Example: She must know the answer.

  Example: They might be watching a movie right now.

Common mistakes

• It can be Ali's bag. It has his name on it. → It must be Ali's bag. It has his name on it.

  For a guess you're sure about, use must, not can.

• She must to be tired. → She must be tired.

  No to after a modal.

• He might knows her. → He might know her.

  No -s after a modal.