有一读者问： 有这样一个句子：
(1)Were it not for their assistance, we couldn't have got over the difficulties.
可否将此句中的 Were it not for their assistance 改为 Had it not been for their assistance? 如可以的话，那么二者有无区别？
were 作为虚拟式是古传下来的一种形式，在现代英语里已逐渐用得少了。当今它主要用于表与现在的事实相反和与将来事实可能相反的条件句中。但它也间或用在与过去事实相反的条件句中，你的引文中的 were it not for their assistance 即是一例。这里的 were it not for their assistance 完全可以代之以 had it not been for their assistance, 二者在意义上并没有什么不同，只是前者稍较文气而已。但须指出，并不是所有用 were 表过去假设的情况皆可代之以过去完成虚拟式。有一些固定的说法至今仍须用 were, 如 if I were you （或 were I you）, if I were in your place （或 were I in your place）, as it were 等。就是像下面这样的句子也常用 were:
(2)If I were not busy, I would have come.
但有时习惯上却不用 were, 如：
(3)If he had been here yesterday, I would have seen him.
