Listen First
Look what I found on the bench. It’s a wallet.
Oh, wow. You should open it to see if there’s an ID. It can’t have been here for long; it’s still dry.
You’re right. Let’s see… There’s no driver’s license, but there is a library card. The name is A. Davies.
A. Davies… I don’t know anyone with that name. It must belong to a student. The library is just around the corner.
That makes sense. Look, there are a few receipts from a coffee shop. The owner might be a regular there.
Or they could have just been meeting someone. They must have been in a real hurry to leave this behind.
I agree. Look, there’s a small amount of cash in here, but no credit cards. They might have taken those out before they left.
Or maybe the cards are in another pocket. The owner must be panicking right now. I would be.
Definitely. We should take it to the library. They might know who A. Davies is.
Good idea. It’s better than just leaving it here. Someone could have taken it.
Life is full of mysteries, and sometimes you have to be a detective! Modals of deduction are your tools for making logical guesses and expressing how certain you are about something, whether it’s happening now or happened in the past. 🕵️♀️
Function & Usage
We use these modal verbs to make a guess or conclusion based on evidence. The modal you choose shows your level of certainty.
- Must (Strong Certainty – Positive): You are almost 100% sure something is true.
Example (Present): He’s been yawning all day. He must be tired.
Example (Past): The ground is wet. It must have rained last night. - Can’t (Strong Certainty – Negative): You are almost 100% sure something is impossible.
Example (Present): That can’t be the right answer. It’s too easy.
Example (Past): She can’t have finished the book already! She only started it an hour ago. - Might / Could / May (Possibility / Weak Certainty): You think something is possible, but you are not sure (around 50% certain).
Example (Present): I’m not sure where Sarah is. She might be in a meeting.
Example (Past): The traffic was bad. They might have missed their flight.
The Structure (Form)
The structure changes depending on whether you are making a guess about the present or the past.
| Time | Structure | Example |
|---|---|---|
| Present | Modal + Base Verb | She must be sick. / They might know. |
| Past | Modal + have + Past Participle | She must have been sick. / They might have known. |
Common Mistakes to Avoid
- Using the wrong verb form for past deductions: Always use `have + past participle`. Incorrect: “He must have went home.” Correct: “He must have gone home.”
- Confusing `can’t` and `mustn’t`: For negative deductions, we use `can’t`, not `mustn’t`. `Mustn’t` is for prohibition. Incorrect: “That mustn’t be true.” Correct: “That can’t be true.”
Let’s see it in action! 🎬
Person A: The lights are on in John’s apartment.
Person B: He must be home then. Let’s go say hello.
Friend 1: I can’t find my phone anywhere!
Friend 2: You might have left it in the car. We should go and check.
Person A: Sarah isn’t answering her phone.
Person B: That’s strange. She can’t have forgotten about our meeting, she was so excited about it.
Check Your Understanding! ✅
1. (100% sure) He looks very unhappy. He a bad day. (have)
2. (100% impossible) You just ate a huge lunch! You hungry again. (be)
3. (50% possible) I’m not sure why she is late. She stuck in traffic. (be)
4. (100% sure) The computer is off. Someone it off. (turn)
5. (100% impossible) He studied for weeks. He the exam. (fail)
6. It ___ rained last night. The streets are all wet.
7. “Where is my wallet?” “I’m not sure. You ___ left it at the restaurant.”
8. You haven’t eaten all day. You ___ be hungry.
9. That ___ be Maria’s car. Hers is blue, not red.
10. He ___ the email. He never checks his inbox.
