Could/Might + Have, Should/Ought To + Have, Must + Have, Would + ...

Could /Might + have + V3: có lẽ đã — dùng để nói về thứ mà ta muốn làm trong quá khứ, đã có cơ hội để thực hiện điều đó.

• I could have moved out when I was 18, but I didn’t want to leave my family. (I chose to stay)
• I might have moved out, but I didn’t want to leave my family. (I chose to stay)
• I could have gone out with my friends but I wanted to watch the soccer game on the TV. (I could but I didn’t go with them)
• I might have gone out with my friends but I wanted to watch the soccer game on the TV. (I could but I didn’t go with them)

Ở cả 2 câu, sự việc đều có thể thực hiện nhưng tôi lại chọn ở nhà xem bóng

Should/Ought to + have + V3: lẽ ra nên, lẽ ra phải — trong quá khứ, chúng ta đã không làm việc gì đó mặc dù nó là việc nên/phải làm. 

• You should have checked your answers thoroughly before you handed in your exam. (but you didn’t which was a mistake)
• You ought to have checked your answers thoroughly before you handed in your exam. (Same but stronger than should have)

Must + have + V3: chắc là đã, hẳn là đã — khi nói về ý kiến của bản thân về những sự kiện trong quá khứ dựa vào kinh nghiệm/sự thật. 

• Do you know Ryan’s math grade?
• I don’t know but he must have got an A. (His math is really good)

Would + have + V3: có lẽ đã — dùng khi nói về sự việc trong quá khứ, mình chọn làm nhưng đã không làm vì điều kiện không đủ, hay vì tình thế không cho phép.  Thường dùng kết hợp với mệnh đề IF.

• I would have moved out, but I hadn’t had enough money. (I wanted to move out but I didn’t have money)
• I would have been smiling if you had brought me some flowers. (You didn’t bring me flowers, so I am not smiling)

Couldn’t Have + V3: đã không thể — dùng để nói về sự kiện trong quá khứ chúng ta muốn làm nhưng đã không làm được.

• I couldn’t have visited you when I was in Paris as I didn’t know your address. (I didn’t visit you when I was in England but it was not possible anyway)

Negative Modals + V3 Table

Examples: One of them —- be lying and I suspect it’s Emma. a)must   b)may   c)must have   d)can’t   e)mustn’t

When did you go shopping last? It —- ages ago. a)must be   b)may be   c)must have been   d)could be

Jane —– about the meeting as she didn’t mention about it at all. a)must hear  b)must have heard  c)can’t have heard  d)couldn’t have heard e)needn’t have heard f)was able to hear

Reference: http://www.grammarbank.com/could-should-would-must-have.html