• "The door's unlocked but no one's in — she must have popped out for a minute."
• "He can't have read my message — he'd never ignore something like that."
• "They couldn't have gone far without a car; the last bus left an hour ago."

What's the shared machinery, and what's the difference between the first sentence and the other two? Say it, then check.

1. You get home and the biscuit tin is empty except for crumbs, and the lid's not even back on. Deduce with must have + eat:

"Someone the whole tin."

2. Your flatmate says she posted your parcel yesterday, but the post box on the corner has had an "out of order" sign on it all week. Use can't have + post:

"She it there — that box's been broken for days."

3. A friend claims he ran the whole route in under two hours, but you know he's never managed more than 5k in one go. Use couldn't have + run:

"He it that fast — he's never run more than 5k!"

• "The line's been busy for an hour — she might have left the phone off the hook."
• "He may have forgotten it was today; he's been so distracted lately."
• "I could have left my keys at the office, or maybe in the car — I'm honestly not sure."

How is the confidence here different from must have and can't have? Say it, then check.

1. Your friend hasn't replied to any texts all weekend, but he's sometimes just busy and bad with his phone, nothing more sinister. Use might have + lose:

"He his phone somewhere, or he's just been busy — hard to say."

2. The vase is broken on the floor. The cat was in the room, but the window was also open and it's been windy. Use may have + knock:

"The cat it over, but that gust of wind is just as likely."

3. Your colleague is late for the meeting — could be traffic, could be an earlier appointment running over, nobody actually knows. Use could have + go:

"She straight to the client's office instead — we don't actually know."

• "Her eyes are red — she must have been crying."
• "The engine's still warm; it can't have been sitting here long."
• "He looked exhausted at the meeting — he might have been working all night."

What's the one extra piece these sentences add? Say it, then check.

1. The bathroom floor is soaking wet and the shower's still steamy when you get there. Use must have been + shower:

"Someone for ages — the floor's flooded."

2. The neighbours upstairs are usually loud, but it was dead silent all evening. Use can't have been + argue:

"They up there tonight — not a sound, which isn't like them."

3. A colleague seemed distracted and miles away in the meeting, and you're not sure why. Use might have been + worry:

"She about something — she wasn't really listening."

You get home and three things are different: the front door's unlocked, there's a coat on the chair that isn't yours, and the dog is nowhere to be seen.

Talk for one minute. Work out loud through what must have happened, what can't have happened, and what might have happened.

Write 3–5 sentences about a real (or invented) small mystery — a missing object, a strange noise, a friend who went quiet. Use at least two different levels of certainty from today; the checker will tell you which it finds.

1. Her coat's still on the chair and the lights are on, but she's nowhere in the office. "She ___ home yet — she'll be back any second, probably just at the printer."

2. Nobody knows why the meeting was cancelled; the organiser hasn't explained anything. "It ___ postponed because of the storm, or maybe something else came up — who knows."

3. You walk past the gym at 6am — the lights are already on and music's playing loudly. "Someone ___ before work, judging by the noise."

4. "He mustn't have seen the email, he never replies that fast normally."

5. "She must had left already — her car's gone."

6. "They can't have went to the party without telling us."

7. "I might have forget where I put my keys."

1. The blinds are down and it's a weekday afternoon, but you can hear music playing inside. Guess about right now, not the past:

"She home already, judging by that music."

2. There's a takeaway receipt on the kitchen counter, and nobody's admitting to ordering it. Use must have + order:

"Someone a takeaway last night — look at this receipt."

3. The car engine's still warm to the touch. Use can't have / couldn't have + drive:

"He far — the engine's still warm."

4. Nobody's announced why the flight was delayed. Use might have / may have / could have + delay:

"It because of the weather, but nobody's said anything official."