连接词“in case,lest,for fear that”可以用来引导虚拟语气.其形式通常为：“…lest (in case,for fear that) +主语+ should +动词原形”.Lest,for fear that句中的should可以省去,in case句中的should通常不省去,但是in case句中可以不用虚拟语气,而用陈述语气.Lest,for fear that后面也可以接其他形式.例如：
He took his coat with him in case it should rain.他带着雨衣以防下雨.
I will not make a noise for fear that I (should/ might) disturb you.我不会做声的,以免打扰你.
Care must be taken in using this method lest overflow (should) occur.在使用这以方法的时候要谨慎小心,以免发生溢流现象.
想要知道更多虚拟语气的用法,可以看下这个网址,介绍的挺详细的