English Grammar : Modal auxiliaries : Could, Should, Might, Must, Ought to + have + Verb 3

Learn Grammar| English Grammar : Modal auxiliaries : Could, Should, Might, Must, Ought to + have + Verb 3 | 1. Could + have + Verb 3
This Modals are used to express the real thing can be done in the past.
He could have done his homework
This implies that he will not do his homework last night.
He could have invited them.

Modals are often used in conditional sentences, especially type II.

2. Should + have + Verb 3
This modal is often used to express something that can actually be done in the past.

She should have sent the letters last week.
This sentence implies that he has not sent the letter last week.

3. Might + Have + Verb 3
This Modals are used to express a prejudice against something that probably already happened in the past.

He might have gone to his office.
They might have finished their duties.

4. Must + Have + Verb 3
This Modals are used to indicate a certainty of a thing must have happened in the past. Basically, this is also conjecture.
He must have studied hard last night.
Niken must have given her photograph.
5. Ought + have + Verb 3
This Modals are used to declare a matter that should have been done in the past.
He ought to have told her about the news.

Modal auxiliary + Have + been + verb-ing , which states that the alleged definitely not taking place at a certain time in the past.

He was holding a newspaper. He can't have been writing a letter.
Niken can't have been playing the piano, she was reading her book when I came. 
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