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future perfect tense ¹

核心问题

In the next few chapters, once we have understood Newton's Law, we shall apply it to the motions of the moon and planets. (PSSC, Physics, Chap. II)

[原译]在以下几章里,我们将运用已经学过的运动定律来研究月球和行星的运动。(《物理》(二),科学出版社,p.296)

请问从句中的 have understood 是现在完成时吗？

词典解答

once 从句中的 have understood 并不是现在完成时,而是将来完成时。

英语动词的将来完成时表示在将来的某一时间点之前业已完成的动作。动词的将来完成时由 shall/will + have + v-ed 构成。例如：

  1. I hope we'll have got the instructions ready before you come tomorrow. 我希望明天你来之前我们已把说明书准备好了。

  2. By the end of this month, we shall have carried out our production plan. 到本月底我们将完成生产计划。

  3. We'd better wait till 14 December. David will have had his exam by then so he'll be able to enjoy himself. (PEG) 我们最好等到12月14日。到那时大卫就考完试了，这样他就能痛痛快快地玩一玩。

  4. The Church will have won their age-old war to rewrite history. The past will be erased for ever. (Dan Brown, The Da Vinci Code) 罗马教廷将会打赢这场世纪之战，从而改写历史。历史的真相将永远被抹去。（《达·芬奇密码》）

但是，在时间或条件状语从句中，当需要表达将来完成时的意义时，则须用现在完成时来代替将来完成时，即用 have + v-ed 结构来代替 shall/will + have + v-ed 结构。例如：

  1. I will repair your bicycle when I have finished this job. 我做完这项工作之后就修理你

的自行车。

  1. By the time the pressure has fallen to atmospheric pressure, the temperature will drop also to the steam temperature at that pressure. 当压力降到大气压力时，温度也将降到常压下的蒸气温度。

  2. We'll start at five o'olock if it has stopped raining by then. 如果到了五点钟雨停下来的话,我们就在五点钟动身。

  3. When I have done that, I shall have done all I was supposed to do. 做了这件事,我就做完了我应做的全部事情了。

  4. After we have learned to control the distribution of atoms and defects in metals more closely than is the case today, we should be in a position to evolve materials with highly selective combinations of physical and plastic properties for use in the special application which advances in engineering science will create. 在我们学会了比现在更加严格地控制金属中的原子分布和缺陷以后，我们就能够研制出一些新材料，这些新材料的物理性能与塑料性能的组合情况具有很大的选择性，能适应工程科学进展所提出的特殊用途。

现在我们再回过头来研究一下你所提问的句子，便可以很容易地看出，从句中的 have understood 尽管在形式上是个现在完成时，但实际上却是个将来完成时（从属连词 once 和主句的谓语动词 shall apply 明显地表达出来了这一点）。原译文的译者显然是误解了这一点，因而把 have understood 译成了“已经学会”。“已经学会”，表示作者写这句话时已经学会，而这是与原文将来完成时意义相违背的（在作者写这句话时，作为该书读者的学生尚未学到牛顿定律），试比较：“他已经走了”。

[试译]在以下的几章里,待我们学会了牛顿定律之后,我们将运用它来研究月球和行星的运动。

练习题

请做下面的英语试题：

  1. He will have learned English for eight years by the time he ____ from the university next year. A. will graduate B. will have graduated C. graduates D. is to graduate(上海高考,02-23)

  2. It's reported that by the end of this month the output of cement in the factory ____ by about 10%. A. will have risen B. has risen C. will be rising D. has been rising(全国四级,96.1-39)

  3. The conference ____ a full week by the time it ends. A. must have lasted B. will have lasted C. would last D. has lasted(全国四级,97.1-22)

  4. “May I speak to your manager Mr. Williams at five o'clock tonight?” “I’m sorry. Mr. Williams ____ to a conference long before then.” A. will have gone B. had gone C. would have gone D. has gone(全国四级,00.6-41)

  5. By the time he arrives in Beijing, we ____ here for two days. A. will have stayed B. shall stay C. have been staying D. have stayed(全国四级,01.6-31)

  6. By the time you get to New York, I ____ for London. A. am leaving B. shall have left C. have already left D. would be leaving(全国四级,02.1-50)

  7. By the time you arrive in London, we ____ in Europe for two weeks. A. shall stay B. have stayed C. will have stayed D. have been staying(全国研考,94-1)

来源：英语常见问题解答大词典-3.md · 第 11390—11459 行 · 原文哈希 67cbe1ad94…