Weakest to strongest
Six claims about the same situation. Put them in order, from the least committed to the most committed.
Six exchanges
Overheard, in an office and a kitchen
— Her coat’s here but her bag’s gone. — Then she must be coming back. Nobody leaves a coat in November.
— Do you think he’s annoyed? — He might be. He might also be tired. He’s been on nights.
— It can’t be the printer. I replaced the printer on Thursday. — Then it must be the network, because there isn’t anything else in the chain.
— She may not want to talk about it. — She may not. But not asking is also a decision.
— That could be him at the door. — At half past eleven?
— It can be very quiet in here in August. — It can. Not today, though.
Four questions about the six exchanges.
1. In the first exchange, what does must rest on?
2. In the third exchange, why is must justified?
3. The last exchange uses can, and it is not deduction. What is it?
4. Could you replace must be coming back in the first exchange with can be coming back?
The system, including the hole in it
The present scale
| Form | Claim | Example |
|---|---|---|
| must + verb | The only explanation left | He must know her — he said her name. |
| must be + -ing | The only explanation, about right now | She must be working late; the light’s on. |
| might / could / may + verb | One live possibility among others | He might know her. |
| might / could / may be + -ing | One live possibility, about right now | He could be waiting outside. |
| might not / may not + verb | Possibly not — the negative of might | She might not know yet. |
| can’t / couldn’t + verb | Eliminated | He can’t know her — they’ve never met. |
| can’t be + -ing | Eliminated, about right now | She can’t be sleeping; the radio’s on. |
The three shapes people get wrong
| Wrong | Why | Right |
|---|---|---|
| mustn’t is prohibition — Unit 10 — and it keeps that job here | She can’t be at home. | |
| English has no positive can for deducing about one case | He must be / might be her brother. | |
| Modals take the bare verb — no to | She must be tired. |
The asymmetry, plainly. On the positive side, English has must at the top and might / could / may in the middle — and nothing else. On the negative side it has can’t at the bottom and might not / may not in the middle.
So the pairs are crossed: the opposite of must be is can’t be, and the opposite of might be is might not be. There is no single word that negates must by keeping must.
Ten sentences. Match each to what it actually claims. Two pairs differ by one word only.
Five questions.
1. Her phone is off and her car is in the drive. Which?
2. The light is on in the office at ten at night. Which?
3. You have three explanations and no way to choose between them. Which?
4. She may not have heard yet. What does this claim?
5. Which of these is about Augusts in general rather than about today?
Evidence in, strength out
One to three words per gap. Some gaps need a continuous form.
The kitchen light is on and the car is here, so somebody at home. It be Nadia, because she flew to Lisbon this morning. It be her brother — he has a key — or it just be a lamp on a timer, which she does when the flat is empty. If it is her brother, he the football, because I can hear a crowd. He asleep, at any rate.
Seven sentences. One error each. Say what the corrected sentence claims.
1. He mustn’t be in the office — his badge hasn’t been used today.
2. She must to be on the later train.
3. That can be his sister — they have the same laugh.
4. The radio is on, so she can’t sleeping.
5. He might not be at the gym, so he is at home. — the first half does not give the second
6. It must be the network. Or possibly the printer. — two live options
7. She may not use this entrance after six. — you mean it is possible she does not know about it
Where are they right now?
Task card · Speaking · Pairs · 8 minutes, fast
A thinks of somebody they both know and decides where that person is at this moment. B asks yes/no questions.
After every answer, B must say one graded deduction aloud before asking the next question.
- B’s deduction must use must, can’t, might, could or may — and must follow from the answer just given.
- A may challenge any must or can’t with "what rules out the alternatives?"
- A challenged claim that cannot answer drops to might, and B loses the question.
- Six questions maximum. Then swap. Two rounds each.
Why the deduction has to be said out loud. Asking questions is easy and teaches nothing. The work is in converting an answer into a claim of the right strength, at speed, with somebody ready to challenge it.
What got challenged
Two questions.
1. Which word did your partner challenge most?
2. What usually happened when you tried to answer the challenge?
Five words, one hole
Two questions. Twenty seconds.
1. What is the opposite of She must be at home?
2. Which does English lack?
Next. The same five words, aimed backwards — and the reason must’ve is one of the most misheard sounds in English.