用法
表示從過去某一時間來看將來某時會已經完成的動作。
如： I thought Sophia would have told you something.
我想索菲婭會已告訴你一些情況。
He knew by the time he arrived she would have gone home.
在他到時他才知道她已經回家了。
The day was drawing near when we would have completed the reservoir.
我們建成水庫的日子不遠了。
He said he would have done with my camera by the end of next month.
他說到下月底就不用我的照相機了。
I guessed that Mother would have made some sandwiches by the time we got back.
我猜我們回來時媽媽已經做好一些三明治了。
用於虛擬語氣中
若表示與過去事實相反的虛擬語氣，此時條件從句的謂語用過去完成時(had+過去分詞)，而主句謂語則通常用過去完成時（would+have+過去分詞），當然，主句謂語也可根據情況使用“should (could, might)+have+過去分詞”。
如： If I’d left sooner, I'd have been on time.
要是我早點動身，我就準時到了。(但我動身太遲了)
If we had found him earlier we could have saved his life.
要是我們當時早點找到他的話，我們就可以救活他。(可惜我們找到他太晚了)
If I had known that you were coming I would have met you at the air-port.
要是我早知道你要來的話，我就會在機場接你了。
If he had lived, some day Michael would have done something important.
假定麥可當時在世的話，他本可做出了不起的事。
If I had known how he felt, I would never have let him adopt those children.
我要是知道他的想法，我是決不會讓他領養那些孩子的。
He would have forgotten the boy’s birthday if you hadn’t reminded him.
要不是你提醒他，他會忘記這男孩的生日的。
Our lives would have been greatly impoverished if we had not known our dear friend.
若不是得識我們這位好朋友，我們的生活一定十分不妙。
“would + have + 過去分詞”的
情態用法
“would + have + 過去分詞”的情態用法
would 後接完成式除用於構成過去將來完成時外，它還有其情態動詞用法的一面。
如： Only somebody with a small mind would haverefused to help.
只有心胸狹窄的人才不肯幫助別人。（表推測）
Few men would have bared their soul to a woman as he had.
很少有男人能像他一樣對一個女人敞開心扉。（表懷疑）
I’m surprised you didn’t like the film. I would have thought it was just your kind of thing.
你不喜歡這部電影，這讓我感到奇怪。我本來還覺得正對你的路呢。（表過去的想法）
My father would have driven me to Cornwall, but we decided it would be quicker by train.
父親原本要開車送我去康沃爾，但我們還是覺得坐火車更快。（表過去的想法）
The scar added interest to a face that otherwise would have appeared too bland.
這處傷疤為本顯得平淡無奇的臉增添了些吸引力。（表示未曾發生的情況）
