Past modals of deduction

Use modal perfect forms to make deductions about what probably, possibly or certainly did not happen.

When do we use it?

Use must have, might have and cannot have plus a past participle.

Form

Use must have for strong certainty, might have for possibility and can’t have for impossibility.

• She must have forgotten.
• They might have left.
• He can’t have seen us.

Key contrast

At B2, choose the form from the complete context: sequence, viewpoint, degree of certainty and clause structure all matter.

Common mistakes

• She must had forgotten. → She must have forgotten.
• He can’t saw us. → He can’t have seen us.

Remember

Use modal perfect forms to make deductions about what probably, possibly or certainly did not happen.

Quick check

• Identify the time relationship or intended meaning.
• Check the auxiliary, participle and clause pattern.
• Eliminate answers that fit the words but not the context.