She must have left · He can't have known · You should have told me · You needn't have
Building on B2
From deductions about now to deductions about the past
At B2 you made deductions about the present: She must be tired. At B2 you make them about the past, and use modals to criticise, regret and talk about what was necessary.
modal + have + past participle
Deduction about the past
must have · might / could have · can't have
about 95% yes
The streets are wet. It must have rained.
possible
She might have missed the bus. · He could have forgotten.
about 95% no
He can't have seen us — he didn't wave.
The opposite of must have is can't have (or couldn't have).
should have · shouldn't have
Criticism and regret
You should have told me!
You didn't tell me — that was wrong.
I shouldn't have eaten so much.
I did — and I regret it.
You could have asked me!
Possible but you didn't — mild criticism.
could have
A possibility that did not happen
We could have won — we played well.
It was possible; we didn't win.
That was dangerous — you could have been hurt.
needn't have or didn't need to?
Two different stories
I needn't have brought an umbrella.
I brought one, but it was unnecessary.
I didn't need to bring an umbrella.
It wasn't necessary — usually I didn't bring one.
Common mistakes
Where learners go wrong most often
He must have not seen me.
→
He can't have seen me.
negative deduction → can't have
You should told me.
→
You should have told me.
modal + have + past participle
She might has gone home.
→
She might have gone home.
always have, never has
I needn't have to hurry.
→
I needn't have hurried.
needn't have + past participle
Your turn
Answer out loud — full sentences
Use past modals.
1
Your friend didn't come to class yesterday. What might have happened?