Could have, will have, would have, should have +past participle

·       Could have  is used when we want to indicate that there was a possibility for something to happen, but it did not happen.

E.g.,

I could have studied better. ( But I did not.)

You could have attended the wedding. ( But you did not.)

·       Will have is used when we are looking back from a point in time,  when something will have happened.

E.g.,

Suresh will have reached home by now.

The over-bridge work will have been completed by 2014.

·       Would have  is used as the past tense of  will have.

E.g.,

I knew that my sister would have finished cooking by 1 p.m.

I did not want to go to my brother’s house at this time. He would have gone to sleep.

·       Would have  is also used for past conditionals.

E.g.,

If you had studied better, you would have scored higher marks.( You did not study; you did not get the marks).

If she had started earlier, she would not have missed the train. ( She started late and missed the train.)

Note:

Some people wrongly use would have instead of had.

If you would have asked me, I would have given you the money.

It should be…..

If you had asked me, I would have given you the money.

·       Should is used to indicate that doing something is a good idea.

E.g.,

You should buy this book. It is very useful.

Imagine that you did not buy the book. When you went to the shop the next day to buy it, it had been sold out. What do you say, then?

I should have bought the book yesterday.

More examples:

You should have listened to my advice.

We should have booked the tickets earlier.

( *Some more will follow. I don’t want to give too much in one go.)