4)完成时的用法 A)Use of present perfective Present perfective,a combination of the perfective aspect with the present tense (have/has +-ed participle )has two chief uses:finished"use and "unfinished"use. The finished"use refers to the present result of a past event still operative at the present moment.The "unfinished"use of the present perfective denotes that an action or state extends over a period lasting up to the present moment,possibly extending into the future as well
1 4)完成时的用法 A) Use of present perfective Present perfective, a combination of the perfective aspect with the present tense (have / has + -ed participle ), has two chief uses: “finished” use and “unfinished” use. The “finished” use refers to the present result of a past event still operative at the present moment. The “unfinished” use of the present perfective denotes that an action or state extends over a period lasting up to the present moment, possibly extending into the future as well
The difference between these two uses manifests itself in the fact that in the unfinished"use,the present perfective is commonly accompanied by an adverbial expressing duration,but no such ac- companying adverbial is present in the "finished"use.Compare: 号He's turned off the light.(灯在一个过去时间被关掉， 说话时仍然关着。) He's lived here since1960.(他从1960年来到这里居 住，至今还住在这里，偶尔也可根据上下文理解为刚刚 搬走。) B)Uses of past perfective The past perfective (had +-ed participle)also 2
2 The difference between these two uses manifests itself in the fact that in the “unfinished” use, the present perfective is commonly accompanied by an adverbial expressing duration, but no such accompanying adverbial is present in the “finished” use. Compare: He’s turned off the light. （灯在一个过去时间被关掉， 说话时仍然关着。） He’s lived here since 1960. （他从1960年来到这里居 住，至今还住在这里，偶尔也可根据上下文理解为刚刚 搬走。） B) Uses of past perfective The past perfective (had + -ed participle) also
has two chief uses:"finished"use and "unfinished"use,only with time reference back-shifted to a specified past moment. In the finished"use the past perfective denotes an action or state already in completion before a specified past,and in its unfinished"use,it denotes an action or state extending over a period up to a past moment and possibly into the future in the past,eg: &I had written the article when he came.(已经写完了 文章) By six o'clock they had worked twelve hours..(他们可 能还会继续工作下去)
3 has two chief uses: “finished” use and “unfinished” use, only with time reference back-shifted to a specified past moment. In the “finished” use the past perfective denotes an action or state already in completion before a specified past, and in its “unfinished” use, it denotes an action or state extending over a period up to a past moment and possibly into the future in the past, eg: I had written the article when he came. (已经写完了 文章) By six o’clock they had worked twelve hours. (他们可 能还会继续工作下去)
Note:Past perfective in sentences with when-/before-/after-/ until-clauses Subordinators such as when,before,after unti/can sometimes be used interchangeably when they connect clauses where two actions happen one after another.The general rule is that the earlier happening is expressed by the past perfective and the later happening by the simple past.Compare: When I reached the station,the train had already left. I reached the station after the train had left. I didn't reach the station unti/after the train had left
4 Note: Past perfective in sentences with when-/ before-/ after-/ until- clauses Subordinators such as when, before, after, until can sometimes be used interchangeably when they connect clauses where two actions happen one after another. The general rule is that the earlier happening is expressed by the past perfective and the later happening by the simple past. Compare: When I reached the station, the train had already left. I reached the station after the train had left. I didn’t reach the station until after the train had left
The train had left before I reached the station. 我 Since before and after can indicate time sequence by their own lexical meanings,the two actions happening one after another can both be expressed by the simple past in sentences comprising a before/after-clause. Compare: The train (had)/eft before I reached the station. After the teacher (had)left the room,the children started talking. Sometimes the past perfective is used in a before-clause to lay emphasis on the incompletion of the action:
5 The train had left before I reached the station. Since before and after can indicate time sequence by their own lexical meanings, the two actions happening one after another can both be expressed by the simple past in sentences comprising a before / after-clause. Compare: The train (had) left before I reached the station. After the teacher (had) left the room, the children started talking. Sometimes the past perfective is used in a before-clause to lay emphasis on the incompletion of the action: