如果你看到下列的句子，你会认为它们是正确的还是错的呢?
1. I wish I were a bird.
2. We request that you be here tomorrow.
也许你会说：“哈哈，第一句的I were 错了，应该是I was;而第二句中的you be是什么东东呀?不是you are, 也不是you will be, 什么you be?!”
其实上面的句子都是一种称为 Subjunctive 类型的句子。Subjunctive Mood 有的书译为“假设语气”，虽不很贴切;但在相当大的程度上，告诉我们这种句子的特点，Subjunctive Mood中文译作“虚拟语气”，似乎不及“假设语气”那么容易明白。它是一种动词形式，表示说话人的某种假设、愿望、怀疑、猜测、建议等含义。
基本上，虚拟语气可分为虚拟现在(Subjunctive Present)和虚拟过去(Subjunctive Past)两种;但它们和时态(Tenses)上所指的现在时态(Present Tense)和过去时态(Past Tense)是有所不同的。
一、虚拟现在(Subjunctive Present)
虚拟现在的句子，在任何时候都要用动词的原形(root form)，就算是第三人称(he, she, it)也是如此。如：
1.1 现在时态(Simple Present)
I work ---- I work
you work ---- you work
he works ---- he work (注意到了吗，是work，不是works)
she works ---- she work (不是she works 喔)
it works ---- it work (同样不是it works 喔)
we work ---- we work
they work ---- they work
1.2 现在进行时态(Present Continuous)
I am working ---- I be working (注意用的是be，怪怪的!)
you are working ---- you be working
he is working ---- he be working
she is working ---- she be working
it is working ---- it be working
we are working ---- we be working
they are woring ---- they be working
1.3 现在完成时态(Present Perfect)
I have worked ---- I have worked
you have worked ---- you have worked
he has worked ----- he have worked (用的还是have喔)
she has worked ---- she have worked
it has worked ---- it have worked
we have worked ---- we have worked
they have worked ---- they have worked
1.4 现在完成进行时态(Present Perfect Continuous)
I have been working ---- I have been working
you have been working ---- you have been working
he has been working ---- he have been working (是he have, 不是he has )
she has been working ---- she have been working
it has been working --- it have been working
we have been working ---- we have been working
they have been working ---- they have been working
