Past Modals of Deduction

Past modals of deduction

Explanation, use, examples, and practice

Introduction

We can use modal verbs for deduction – guessing if something is true using the available information. The modal verb we choose shows how certain we are about the possibility. This presentation focuses on making deductions about the past.

Structure

To make guesses or deductions about past actions or states use a past modal of deduction. This is formed with a modal verb + have + past participle also called the perfect infinitive.

Where's my phone? You could have left it in your office. To make deductions about continuous actions or states use the modal verb + have + been + ing form. Why didn't Sarah come to the party last night? She must have been feeling ill.

We use must have + past participle when we feel sure about what happened. Who told the newspapers about the prime minister's plans? It must have been someone close to him. The thief must have had a key. The door was locked and nothing was broken. Oh, good! We've got milk. Mo must have bought some yesterday.

Must have

We can use might have or may have + past participle when we think it's possible that something happened. - I think I might have left the air conditioning on. - Please can you check? Police think the suspect may have left the country using a fake passport.

May have is more formal than might have. Could have is also possible in this context but less common.

might have / may have

We use can't have and couldn't have + past participle when we think it's not possible that something happened. She can't have driven there. Her car keys are still here. I thought I saw Adnan this morning but it couldn't have been him – he's in Greece this week.

can't have / couldn't have

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Past Modals of deduction

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Practice

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4. Practice

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