虚拟语气中的含蓄条件句常见用法先看一道高考题：
___ more attention ，the trees could have grown better ．
A．Given B．To give C．Giving D ．Having given
(答案是A )
句中" ．．．the trees could have grown better" 是一个表达虚拟语气的句子。题中要求选择的是如何表达假设条件的形式。如果我们把这个句子用另一种形式"If they had been given more attentio n ，the trees could have grown better ．" 来表示，就不难理解了。很多情况下，在表示假设的虚拟语气中，有时假设的条件并不以条件从句的形式表达，而是通过上下文或句中内在的逻辑关系，或用其它形式表达出来，我们称之为" 含蓄条件句" 。含蓄条件句主要通过名词、连接词、不定式、分词、动名词短语、介词短语及分句来暗示。这些表达形式在句中实际起着虚拟条件从句的作用。现分述如下：一、介词短语常用来表示虚拟条件的介词有with ，without ，in ，under ，but for 等等，它们表示的虚拟条件都可以被if 从句替换。
( 1 ) without ，with
without 表示否定的条件，意为if ．．．not ；with 与without 意义相反，表示肯定的条件。如：
Without air , there would be no living things .(without air = if there were no air)没有空气，便没有生物。
With her help (= If I had her help )，I would do the experiment well ．假如有她帮助，我就可以把这个实验做好。
( 2 ) under
Under the leadership of a less experienced person ，the experiment would have failed ．( u nder ．．．= If there had been the leadership of a less experienced person )假设在一个缺
少经验的人领导下进行实验，实验准会失败。
(3 ) in
I would have lost my head in that position ．( in that position = if I had been in that po sition )我处在那种情况下，是会丧失理智的。
( 4 ) but for
But for their help (= If it were not for their help ) , we could not get over the difficultie s ．要不是他们的帮助，我们是克服不了这些困难的。二、连接词or ，otherwise ，but ，but that 等等
I'm really busy ，otherwise (= if I weren't so busy )，I would certainly go with you ．我确
实太忙了。不然的话，我一定和你一块去。
But that I saw it (= If I had not seen it )，I could not have believed it ．要不是亲眼看见的话，我是不会相信的。
三、分词短语
United (= If they had been united )，they wouldn't have been defeated ．他们要是团结起来，
就不会被打败。
Seen from a high mountain (= If it were seen from a high mountain )，the field in whi ch wheat is growing would look like a great green sea ．倘若从高山上看，麦田就像一片碧绿的大海。
四、动词不定式短语
It would be only partly right to answer in this way ．(= if we answered in this way )如果这样回答，只对一部分。
To hear him speak English (= If one were to hear him speak English )，one would think him an Englishman ．要是听他讲起英语来，人们会认为他是一个英国人。
五、形容词或其比较级的形式
A less difficult problem would have already been solved ．(= If the problem had been l
ess difficult ，it would have already been solved ．)要是问题不那么难的话，它早就被解决了。
An honest man would not do such a thing ．(= If he were an honest man ，he would no
t do such a thing ．)诚实的人是不会做这种事的。
六、名词
An honest man would not say this ．(= If the man were honest ，he wouldn't say this ．)
一个诚实的人，就不会说这种话。
Who but a fool (= If one were a fool ，one )would believe his words ．除了傻瓜，谁会相信他
的话！
七、"名词＋and" 的结构
One step further and you would be dead .(= If you took one step further , you would be dead ．)再往前走一步，你就会死。
八、独立主格结构或由with 引导的复合结构
All things considered (= If all things were considered ) , the price would be reasonable .女口果全面考虑起来，价格可
