1 it is great to him --------裏面的 it 往往是真正主语: it (== such work) is great to him. to是介词,解释为“对 -- - 来说”。 2 it is great for him ------裏面的 it 往往是形式主语,而真正主语在已知的语境中被省略了: It is great for him (to do such important work). ------这里的 to do such important work== it ,是真正主语,for him 是逻辑主语。