由于were型虚拟式主要用在if非真实条件句中，而且它是其他were型虚拟式句型的基础，所以我们先要搞清楚if非真实条件句。

　　(1) if非真实条件句:

　　条件句分为真实条件句和非真实条件句：

　　真实条件句是指真实的或可以实现的条件句，例如：If we work together, we are sure to finish the task in time. (如果我们大家一起努力，就一定能按时完成任务)，动词使用的是真实的时态和形式。

　　非真实条件句是指对已经发生过的事情，或对不可能发生或实现的事进行假设，例如："如果当时有医生在，这个孩子就有可能得救了"，显然，这是对已发生的事情的一种假设，该句的英语表达为：If there had been a doctor available, the child might have been saved.

　　为了便于理解和记忆，我们用表格形式加以归纳：

　　时间动词形式举例

　　过去if条件句：had done / had been

　　结果句：would have done / been If there had been a doctor available, the child might have been saved.

　　倒装：Had there been a doctor available, the child might have been saved

　　现在if条件句：did / be动词用were

　　结果句： would do (be) If I were you, I would accept his offer. (如果我是你的话，我就接受他的提议。)

　　倒装：Were I you, I would accept his offer.

　　If I knew the fact, I would tell you. (我要是知道，我就会告诉你)

　　不可以倒装

　　将来if条件句：

　　should do (be) / were to

　　结果句：would do (be) If it should rain tomorrow, we would stay at home. (一旦明天下雨，我们就呆在家里。)

　　倒装：Should it rain tomorrow, we would stay at home.

　　If he were to come this evening, I would ask him to help solve the problem. (要是他晚上会来，我就请他帮助解决这个问题。)

　　倒装：Were he to come this evening, I would ask him to help solve the problem.

　　这里关键是要掌握好两点：

　　(A) 虚拟行为或状态发生的时间：过去?现在?还是将来?

　　(B) 采用了什么相应的动词形式?