he took his raincoat with him in case it should rain中should能

在某些词后面可以省略这个should,但是should前面必须有间接宾语
比如suggest,command和insist,有点使令性的意思的动词
由于should其实是被省略的,之后的动词使用原型,比如he suggests you （should） take the money back
但是前面的suggest还是需要根据情况变形,由于这个是句子的谓语
如果是he would suggest you （should）take the money back,这个句子中由于有了would,之后的谓语动词不变形.不知道这么说你明白不
如果suggest后面直接加动词,需要变成ing形式,比如he suggests taking the money back或者he would suggest taking the money back
此处是should表示虚拟语气 以防下雨 不能省