– Bianca is not here. She must be at school. (= or more than 90% YES)
100% – certain: Bianca is at school.
– Rares comes today, but he is late. He might be on the bus. (= or more than 50%)
100% certain: Rares is on the bus.
– Father is not here, where is he?
I don’t know, he could be in the supermarket. (= or more than 50%)
100% certain: Father is in the supermarket.
– Where is the father? It is so late, he can’t be still in the supermarket.! (= or more 90% NO)
When we express deduction or make a guess, we don’t use ‘mustn’t’ as the opposite of ‘must‘, but ‘can’t‘.
‘Can’t’ is the opposite of ‘must‘.
90% YES -> MUST
90% NO -> CAN’T (not mustn’t)
50% YES -> COULD or MIGHT
Exercise: Use must or can’t
- Andra isn’t at school. (100% = certain)
Andra can’t be at school (90 % NO)
- All the children are in the restaurant. (100% = certain)
All the children must be in the restaurant. (90% YES)
- The test isn’t difficult. (100% = certain)
The test can’t be difficult. (90% NO)
- Where is Rares, he is not here.
He is on his way. (100% = certain)
He must be on his way. (90% YES)
- The Pharmacy/Chemist isn’t closed. (100% = certain)
The Pharmacy/Chemist can’t be closed. (90% NO)