语法规定而已,死记即可,只能是大家约定俗成的习惯.
非谓语动词的完成式,不但不可以做后置定语,也不能做宾语/主语补足语,一般只能做状语.
其中动名词的完成式还可以做主语/宾语/表语.
如：His having finished his homework enabled him to watch TV all day yesterday.