赖世雄教你学英语语法
虚拟语气
5-4：if he is nice...
if he is nice...= if he be nice...
纯条件虚拟语气中的if从句动词时态为现在时，亦可改为原形动词。
例：if he takes my place, i shall not have to go.
= if he take my place, i shall not have to go.
（如果他代替我，我应该就不必去了。）
if he is nice, i will make friends with him.
= if he be nice, i will make friends with him.
（如果他人很好，我会和他做朋友。）
但此类使用原形动词的结构毕竟少见，故同学不直使用，仍以现在时的写法为佳。