在表示假想的虚假的、与事实相反的或难以实现的情况时用虚拟语气，表示主观愿望或某种强烈情感时，也用虚拟语气。下面我们来看一下英语虚拟语气的三种时态：
1.对现在的虚拟结构：
if+主语+动词动词过去时，主语+should/would+动词原形 ，should不可以省略。
If I knew his telephone number，I would tell you.
如果我知道他的电话号码，我就会告诉你。
2.对过去的虚拟结构：
if+主语+had+过去分词，主语+should/would+have+动词过去时。
If he had taken my advice，he would not have made such a mistake.
如果他听我的劝告的话，就不会犯这样的错误了。
3.对将来的虚拟结构：
if+主语+should+动词原形（were to+动词原形），主语+would/should+动词原形，这个should 可以省略。
If she were to be here next Monday，I would tell her about the matter.
如果她下周一来这儿的话，我就会告诉她这件事的始末。
虚拟条件句的从句中如果有助动词were; had或should可以去掉if以后用倒装句语序。
Were she my daughter, I could suggest a different plan .
如果她是我的女儿,我会提出不同的计划。
