Let's start with something you already know — have a go, and don't worry about mistakes.
You know "must" from rules. Complete this sentence with one modal verb:
"In a car, you wear a seatbelt — it's the law."
Out loud: say two more rules of the road in your country, starting "You must..." — anything from speed limits to phones.
Ali: Whose jacket is this? Someone's left it on the chair.
Rosa: It must be Dan's — he was sitting there all evening.
Ali: It can't be Dan's. Dan was wearing his jacket when he left, remember?
Rosa: Hmm, true. Then it might be Priya's — she rushed off to catch her train.
Look again. Nobody has checked the jacket. So how sure is Rosa when she says "must be"? How sure is Ali with "can't be"? And "might be"? Put the three phrases in order of certainty out loud before you check.
For when the evidence is so strong that you're sure — even though you haven't checked.
Three everyday conclusions:
Two questions before you check: what's the structure? And is this the same "must" as "you must wear a seatbelt"?
Complete each conclusion. Type all the missing words, using the word in brackets.
1. Marco got up at 4 a.m. for a flight, and it's now midnight — and he's still answering messages.
"You , Marco — go to bed!" (tired)
2. It's 9 p.m., the lights are still on in the little bakery, and you can smell fresh bread from the street.
"They tomorrow's bread already." (bake)
Say your conclusion out loud for each clue, starting with "must be":
For when you're sure something is impossible. And a famous trap hides here — let's walk straight into it and out again.
Three impossible ideas:
Here's the trap. The opposite of "must be" should logically be "mustn't be"... but that's not what these sentences use. What do they use instead — and can you guess why? Say your idea, then check.
Complete each reply. Type all the missing words, using the word in brackets.
1. Your phone rings and the screen says "Mum" — but your mum is sitting right next to you, and her phone is in her bag.
"That — she's sitting right here!" (Mum)
2. Your friend says Kenji is probably in front of the TV for the big match. But it's 4 a.m. in Tokyo, where Kenji lives.
"He the match live — it's the middle of the night there." (watch)
Disagree with each idea out loud, using "can't be" and giving the reason:
For when something is possible — maybe 50% — and you're honestly not sure.
Three honest guesses:
Three different modals this time. Do they mean three different things, or the same thing? Decide, then check.
Complete each guess. Type all the missing words, using the words in brackets.
1. A tiny light is flashing far away in the night sky, very high up. You honestly don't know what it is.
"It , or maybe a satellite." (a plane)
2. Why isn't Ben answering the door? Hard to say.
"He — he often does after lunch." (have a nap)
3. Choose the right option. Dad left work an hour ago, but the drive home only takes twenty minutes. "He ___ stuck in traffic — or maybe he stopped at the shops."
It's 10 p.m. and your doorbell rings. You're not expecting anyone. Say three different guesses out loud — one with each modal: "It might be... It could be... It may be..."
Time to be the detective. You do the talking.
You're at a café. Your friend Jo is thirty minutes late — no call, no message. Now Jo's phone goes straight to voicemail. Jo is normally never late.
Talk it through out loud for one minute. Work through:
Write a short message (3–5 sentences) to a friend you both know, thinking through where Jo is. Use all three of today's forms — must be, can't be, and might / could / may be. The checker will tell you which ones it finds.
Real life doesn't tell you which form you need. Everything is mixed from here — you decide.
Each sentence has one mistake with today's grammar. Rewrite the whole sentence correctly.
1. Your taxi app says "You have arrived" — but you're standing next to an empty field.
"That mustn't be the right address."
2. Your friend has just come out of the sea. In March. Without a wetsuit.
"You must to be freezing."
3. An unknown number is calling you.
"It maybe is my bank."
4. Someone is knocking at the door and you're not sure who.
"It can be the pizza delivery, or my neighbour."
5. You can hear the shower running, and your flatmate's towel has gone from the hook by her door. "She ___ in the shower."
6. A bus is coming, but yours is the 42 and this one says 15. "That ___ our bus."
7. The baby has finally stopped crying and the house has gone quiet. "Shh — she ___."
One-minute detective challenge. You come home and find: the TV is on, there's half a cup of still-warm coffee on the table, and your sister's shoes have gone. Talk through the mystery out loud: what are you sure of, what's impossible, and what's just possible? Use the timer on the previous page if you like the pressure.
1. The "happening right now" form you learned long ago — complete it: "Look outside — it again." (rain)
2. Say it out loud: "must" has another job that you knew before today. What is it, and what is its negative? Give one example of each.
3. Your friend's daughter got the highest mark in the whole school. Complete your reaction: "You !" (proud)
4. A taxi pulls up outside, but you only ordered yours two minutes ago and the app says "8 minutes away". Complete: "That — I only called two minutes ago!" (my taxi)
5. Dan missed football today and nobody knows why. Complete your guess: "He for work, I suppose." (travel)
Which practice helped you most today — fixing the mistakes, choosing between the forms, or the detective speaking tasks? Say why you think that one worked for you.
At the start we said: must be, can't be and might / could / may be, so you can work things out like a detective. Tick what's true: