I failed my final exam. You ___________ ____________ __________ harder. (study)
You should / ought to have studied harder.
Frank made me a special card. I wanted to show it to you. You _________ ________ _________ it with you. (bring)
You should / ought to have brought it with you.
I'm sure I switched the light off. I...
I must have switched the light off.
When do we use "couldn't / can't have"?
When we are almost sure something didn't happen, or it is impossible.
It definitely wasn't my sister you saw in the mall. It...
It can't have been my sister you saw in the mall.
Why do we use must / may / might / can't / couldn't + have + past participle?
To make deductions or to speculate about the past.
I don't think I'm going to make the meeting. You _______________ __________ __________ your journey better. (plan)
You should / ought to have planned your journey better.
I lost my wallet last night and it had $200 in it. You _____________ __________ _________ so much money out with you. (take)
You shouldn't / oughtn't to have taken so much money out with you.
I think I've missed my flight. You _______________ __________ __________ so late for the airport. (leave)
You shouldn't / oughtn't to have left so late for the airport.
When do we use "must have"?
When we are almost sure that something happened or was true.
I found my Christmas present! That's impossible, I haven't bought it yet. You...
You can't have found your Christmas present.
Mark made a mistake and didn't answer all the questions on his exam paper. He _______________ __________ __________ how many questions there were. (check)
He should have checked how many questions there were.
I'm sure it was raining when he left to go to work. He took his umbrella. It...
It must have been raining when he left for work.
Is Stacy coming to my party? Maybe she didn't get the invitation. She...
She might not have received the invitation.
I need more glue. I didn't buy enough at the market. You ___________ _________ _________ to buy more glue. (forget)
You shouldn't / oughtn't to have forgotten to by more glue.
Jack is laughing. Maybe Sarah just told him a joke. He...
He might have been told a joke.
When do we use "should have / ought to have"?
When we want to say that somebody didn't do the right thing.
When do we use "might / may have, could have"?
When we think it is possible that something happened.
It's tastes a bit funny! Maybe you didn't add enough salt when you were cooking.
You might not have added salt when you were cooking.