条件和假设

一、真实条件从句

从句提出的条件是能实现的。如果该条件实现，则主句所表示的结果也将实现。例如：

1. If a = b and b = c, then a=c. 如果 a=b, b=c, 那么 a=c.
2. If the temperature of water is below 0℃, it exists in the solid state. 如果水温低于0℃，水就处于固态。
3. If Henry comes here, I shall ask him some questions. 若亨利来这里，我将问他一些问题。

二、假设或非真实主从句

从句所表示的假设与事实相反，或者不大可能实现. 一般可分为下列三种假设情况。这时谓语动词要用虚拟语气，以表示所说的话只是一种假设、愿望、猜测而已。（参阅第144节一、三、四、五和六。）

I. 与现在事实相反的假设：这时从句中谓语用过去一般时（be 用 were），主句谓语是“should 或 would（或其它情态动词 could, might 等）+ 动词原形”

1. If Joe had time, he would help you. 假如乔有时间，他就帮助你了。（事实上他现在没有时间。）
2. If I knew English, I should be able to read these English books. 假如我懂英语，我就能读这些英语书了。（实际上我现在不懂英语。）
3. If there were no gravity, there would be on air around the earth. 若没有重力，地球周围就没有空气。（事实上有重力。）
4. If there were no electronic brains, we could not live a modern happy life. 假如没有电脑，我们就不能过现代化的幸福生活. （假设的从句也可换用 If it were not for electronic brains. 详见本节、三、Ⅲ。）
5. Suppose (= If) you had a sum of money, what would you do with it? 假如你（现在）有一笔款子，你会用来做什么呢？（事实上现在你没有一笔款子。）
6. What would happen if human cloning became a reality? 万一人类无性生殖（指克隆人）成为现实，那将会发生什么呢？

II. 与过去事实相反的假设：这时从句谓语用过去完成时，主句谓语是 “should 或 would（或其它情态动词could，might 等）+ 完成时（后者一律用“have + 过去分词”形式）”。

1. If we had known the basic principles. we should have controlled the process even better. 假如我们知道这些基本原理，我们早就能更好地控制这个过程了。（事实上这些基本原理我们当时还是不清楚的。）
2. If you had come here yesterday, you would have seen him. 假如你昨天来这里，你就见到他了。（事实上你昨天没来这里。）
3. If she had further considered the problem, she might have come to the correct conclusion. 假如她当时能进一步考虑这个问题，她也许（会得出正确的结论。（事实上她当时没作进一步考虑。）

III. 与将来事实可能相反（指不可能实现或可能性较小）的假设：这时从句谓语用“should（或其它情态动词could, might 等）+动词原形”或“were + 带 to 的不定式动词”，主句谓语为“should, would 或其它情态动词过去式 could，might 等 + 动词原形”。

1. If Linda should come to us, she would answer these questions. 假如琳达真能来我们这里的话，她会回答这些问题的。（事实上她来的可能性较小或者不存在。）
2. If Sidney were to do this test, he might do it (in) some other way. 要是锡德尼做这项试验，他可能用另外某种方法做。（实际上不是他将去做这项试验。）

三、假设情况的其它表示法

Ⅰ. 用颠倒主、谓语词序手段表示假设条件从句：假设条件从句中谓语有 were, had, should, could 等时，则可去掉 if，把这些词提到从句最前面，即可构成假设条件从句的另一种句型。例如：

1. Were there no gravity, there would be no air around the earth. 假如没有地球引力，地球周围就没有空气.
2. Were Jenny in Tianjin, she would help us. 假如詹妮在天津的话，她是会帮助我们的。
3. Had Dr. Ouyang time, he would help us (to) solve these problems. 假如欧阳博士有时间，他就会帮我们解决这些问题了。
4. Should they come to us, I should ask them some questions. 假如他们真能来我们这里的话，我将问他们一些问题。
5. Had the checking up of the experimental data not taken so much time, we should have completed our work long ago. 假如检验实验数据不花那么多时间，那么我们早就完成这项工作了。
6. Could he have fore seen it, his iron soul must not have been shaken. 假如他当时预知这件事，他铁一般的意志就决不会动摇了。
7. He might live quite comfortably were it not for such troubles. 若没有这样一些麻烦，他会过得很舒服的。
8. People might have avoided many accidents had ultrasonic methods been known before. 要是人们早就知道超声波方法，就可避免许多事故。
9. Did I see him, I would blame him for it. 如果我现在见到他，我就会为那件事责备他了。
10. Many of the successful men, had they been able to choose for themselves, would have selected other different professions. 许多成功的人，如果当初他们能自由选择职业的话，他们会选择其它不同的职业。
11. Should he call, tell him I am not at home. 万一他来叫我，就告诉他，我不在家。（本句假设是对将来事实可能相反的假设，只是实现可能性极小，但毕竟还有一点，故后面主句也可不用虚拟语气。）
12. Should they come (= If they should come), I shall speak to them about it. 如果他们真的来，我就给他们讲讲这件事。（假设的情况与上句相同，还有一点可能性实现，故后面主句也可用将来时。）

现将上述三种假设情况汇总成下列一表：

假设类型	假设条件从句	主句
与现在事实相反的假设	If + 主语 + 动词过去时（be 用 were）或用主、谓语语序颠倒方法	主语（第一人称）+ should + 动词原形 主语（第二、三人称）+ would + 动词原形
与过去事实相反的假设	If + 主语 + 过去完成时或用主、谓语语序颠倒方法	主语（第一人称）+ should + have + 过去分词 主语（第二、三人称）+ would + have + 过去分词
与将来事实可能相反的假设	If + 主语 + should（或 were be）+ 动词原形或用主、谓语语序颠倒方法	主语（第一人称）+ should + 动词原形 主语（第二、三人称）+ would + 动词原形

注： >1. 主句还可用could（能够）, might（或许，可以）代替 should, would 只是含义不同而已。 >2. 现代英语中，主句第一人称也常用 would。 >3. 去掉 if，把从句中 were, had, should, could 等提到从句前面，即可构成假设条件从句的另一种句型。 >4. 当假设用的从句主语为第一、三人称单数时，现在也有人用 was 代之，但采用主语、谓语词序颠倒以省略 if 时，一律用 were，不能用was。 ###II. 用介词短语 "without…" 或 "but for…" 等表示假设条件。 >1. *Without steel* and computers (= *If there were no steel* and computers), there would be no modern industry. 没有钢铁和计算机，就没有现代化的工业。 >2. *But for information technology*, we could not develop our network economy so rapidly. 要不是信息技术，我们不能如此快速地发展我们的网络经济。 >3. *But for the doctor’s high skill*, they would have died. 若没有这位医生的高超医术，他们早就死了。 ###III. 用 "Were it not for + 宾语" 或 "But that + 从句" 表示假设从句的否定式。 >1. *Were it not for* (= *If it were not for* ) *a computer*, you couldn't get on line and send a video e-mail to a friend from over the sea. 假如没有计算机，你就不能入网并且给海外朋友发视频电子邮件。 >2. *Had it not been for a portable phone*, I wouldn't have inform you of that traffic accident in time. 假如当时没有一部移动电话，我那时就不会及时通知你那件交通事故了。 >3. *But that he helps*, I would, fail. 要不是他现在帮忙，我就会失败的。（实际上目前有他帮助。） >4. *But that he saw it* (= *If he had not see in*)，he could not have believed it. 要不是他亲眼看见，他早就不相信了。 ###Ⅳ. 通过上下文表示假设条件；至于属于哪种假设情况，主要看主句的谓语结构和上下文语言环境。 >1. Yesterday I was busy (in) getting things ready for trial production. *Otherwise I would have taken* part in the discussion. 昨天我忙于为试制生产作准备，否则我早就参加那次讨论了。（句中 *Otherwise* 实际上等于一个假设条件，即 "*If yesterday I had not been busy getting things ready for trial production*"。） >2. It *would be* a mistake not to help him. （要是）不帮助他，就会是一个错误。（不定式短语作真正主语）上句相当于：It *would be* a mistake *if we did not help him*. >3. Agnes *would have given* you more help, but she was very busy. 阿格尼丝本来会给你更多的帮助的，但她（那时）太忙了。 >4. This happening in the old society *would have caused* great disasters. 这要是发生在旧社会，早就造成极大的灾难。(句中 This happening in the old society 为具有“主谓”关系的复合结构，作主语。） >5. A true friend *would have acted* differently. （=A friend, if he had been true, *would have acted* differently. ）一个真正的朋友就不会这样做了。 >6. With his aid you *would have succeeded* in it. 若当初就有他帮助，你早就成功了。 >7. That *would be* fine. 那太好了。（省去了 if you should do it. ） >8. (a) *If only* he *were* alive！要是他活着多好啊！
(b) *If only* I *hadn't lost it*！要是没丢失（它）多好！ >9. I *wish* (*that*) I *hadn't* said that. 悔不该当时那样讲了. （原义是：但愿我当时没那样讲多好啊！显然是对过去没实现的事表示遗憾。） >10. He *wishes* (that) you *would stay* a little longer. 他巴不得你多呆一会儿。（实际上可能性不大，你马上要离开。） >11. I *wish* it *were* true. 可惜不是真的. （原义是：但愿这是真的多好啊！宾语从句内容实际上是和现在事实相反的，故用虚拟语气。） >12. How I *wish* it *weren't*（或 *wasn't*）raining! 现在要是不下雨多好！（本句为感叹句结构。） 注：若用 hope 代替 wish，宾语从句改用将来时，那就变为可能实现的希望。例如：I *hope* (that) you *will come* here once more。我希望你能再次来到这里。试比较：I *wish* (that) he *would come*. 可惜他不来。（原义为：但愿他能来多好啊！实际上这个希望落空，故译为：可惜他不来。） ###Ⅴ. 注意某些动词（如 intend, hope, mean, want, plan, think 等）以过去完成时构成虚拟语气，表示本来打算做而实际未做的动作。 >1. Derek *had hoped* to make another experiment, but it was too late. 德立克本来打算再做一个实验的，但是时间太晚了。 >2. We *had intended* to go to the library, but it began to rain. 我们本来想去图书馆的，但是天开始下雨了。 注：这里可联想有些动词（如 plan, mean 等）后用完成时的不定式以表示未实现的动作。例如： >1. I *planned to have left* yesterday. 我本来计划昨天离开的。 >2. He *meant to have told* us about it, but he forgot to do so. 他本想将这件事告诉我们的，但他忘了告诉。