FluencyLab
GrammarHub
Use must, might, could and can't to express how certain you are about a present situation.
Overview
Use must, might, could and can't to express how certain you are about a present situation.
Form and rules
Use must + base verb for a strong positive deduction: She must be tired.
Use can't + base verb for a strong negative deduction: That can't be right.
Use might/could/may + base verb for possibility when you are not certain.
These modals express logical judgment here, not obligation or ability.
Base deductions on evidence or reasoning in the context, not simply on probability words.
A closer look
These modals express logical judgment here, not obligation or ability.
Base deductions on evidence or reasoning in the context, not simply on probability words.
Examples
The lights are on. They must be home.
He can't be sixty; he's only forty.
This key might belong to Ana.
They could be stuck in traffic.
She may know the answer.
Common mistakes
The evidence supports a strong positive deduction.
Known facts make the identification impossible.
Ready to practise?
The test combines multiple choice, gap completion, error correction, and sentence building so students have to recognise and produce the grammar, not simply reread the rule.