Should have / could have / might have (a)

We use should have / could have + past participle

• to talk about unreal past situations that are the opposite of what actually happened:

I should have warned you about the guard dog (= but I didn’t).
We could have gone away for a couple of weeks (= but we didn’t).
I’m not surprised he’s left the company – he should have been promoted here long ago (but he wasn’t).
You were lucky to get away with* a few scratches – you could have broken your leg (but you didn’t).

We can use could have / might have

• to criticise people for not doing things:

You might have mentioned she was a vegetarian! (Why didn’t you?)
She could have dropped a hint about inviting me to stay to dinner. (Why didn’t she?)

*get away with sth – phrasal verb – succeed in avoiding the consequences of sth / punishment for something