1.虚拟条件是指讲话人认为无法实现、不可能存在的条件。在考题中，出题人会将虚拟条件转成其他的“事实”陈述，而不以if-clause的形式出现。
１）与现在事实不符的虚拟条件句
If Professor Zhang were here, he could/would/might/should help us.张教授现在如果在这里，他就能／就会／也许／应该帮助我们。（四个情态动词各表达讲话人不同的讲话态度，要注意选择使用。）
２）与过去事实不符的虚拟条件句
If you had gone to the meeting yesterday, you should have known what was discussed there.昨天，你如果参加了会议，就应该知道会议上讨论了什么。
Had Tom met me before, I might have told him about it.汤姆要是早点儿遇到了我，我也许把这件事告诉过他了。（省略if就要将谓语部分的<第一个>动词调到句首）
