The past of could (do) is could have (done). We use could have (done) to say that we had the ability or the opportunity to do something but did not do it:

 از could have done زمانی استفاده میکنیم که در گذشته توانایی انجام کاری را داشتیم ولی انجام ندادیم.

• We didn’t go out last night. We could have gone to the movies, but we decided to stay home. (We had the opportunity to go out, but we didn’t.)

• Why did you stay at a hotel in New York? You could have stayed with

Linda. (You had the opportunity  to stay with her but you didn’t.)

Why didn’t Tom apply for the job? He could have gotten it. (He had

ability to get it.)

We also use could have (done) to say something was a possibility but it didn’t happen:

• He was lucky when he fell off the ladder. He could have hurt himself.

Here are some examples of couldn’t have (done). I couldn’t have done something” . I wouldnt have been able to do it if I had wanted or tried to do it:

• When I went to New York last year. I decided not to stay with Linda.Later

I found out that she was away while I was there, so I couldn’t have stayed with her anyway.

• The hockey game was canceled last week.Tom couldn’t have played

anyway because he was sick.