They may be in the library now，这名里的maybe 可不可以放最前面？

此 may be 非彼 maybe ！

这儿的 be 是谓语动词，只是在 may 后面才改成原形；如果 maybe 放在句前，谓语动词就没有了；如果把 may be 放在句前，和语法不合，也不行。但是可以这么说，Maybe they are in the library now 。

口语的时候可以
是对自己刚才所讲的事情表示怀疑

they are in the library now, may be!
they are in the library now, I guess

may be是也许是的意思.这个是情态动词+动原.be的动原就是be
maybe 是也许的意思.这个是副词.通常放句首.

They may be in the library now 或者 Maybe they are in the library now