過去完成時(had done)
�、俦硎驹谶^去的某個時間或動作以前已經完成的動作或已經存在的狀態。就是我們常說的"過去的過去"。
Until then, his family hadn't heard from him for six months.
到那時為止，他家里已經有六個月沒得到他的消息了。
②表示從過去的過去開始，持續到過去的動作或情況，并且有可能會繼續延續下去。此時經常用延續性動詞。
By the time I left the school, he had taught the class for 3 years.
到我畢業時,他已經教那個班三年了.
過去完成進行時：had been doing
表示從過去的過去開始，持續到過去的動作或情況，期間一直有規律的在進行、不曾間斷，并且有可能會繼續延續下去。此時經常用延續性動詞。
例：The old clock had been being taken apart of and fixed up again for several times by my 10-year old son before I came back home.
我回到家之前，我10歲大的兒子已經把這個舊鐘表拆卸并重新組裝了好幾回了。
過去將來完成時：(would have done)
表示到過去將來某一時間已經完成的動作，并且對過去將來那一時間點產生影響。
例：I believed by the end of that year an advanced version of that software would have been developed, but I was wrong.
我堅信到那年年底為止，那個軟件的新版本將被開發出來。但是我錯了。
表示動作從過去某一時間開始一直延續到過去將來某一時間，并且有可能繼續延續下去。
例：He told me that by the end of the year he would have lived there for thirty years.
他告訴我，到那年年底為止他將已經在那里住了三十年了。