1、It is important to drink enough water every day.it形式主语,没有意思的,to drink enough water every day真正主语,意思是:每天喝足够的水很重要。为了句子平衡,使用了形式主语,而把真正主语放在后面,所以句型:it‘s+adj+to do的意思是:做某事怎么样。
2、Doctors think it is important to drink enough water every day.这时候It is important to drink enough water every day是宾语从句,作think的宾语。此时,it是形式宾语important为宾语补足语to drink enough water every day为真正宾语。
作逻辑主语
形式主语it作为形式主语的it并无实际语义,只是为满足语法上的需要,避免句子头重脚轻,它代替的是句子的逻辑主语,概括起来会有如下情况:
不定式作逻辑主语
如:It is very kind of you to give me a hand in time.
It is my pleasure to address the meeting.
从句作逻辑主语
如:It is so happened that the tickets were sold out.
It is extremely obvious that she has been lying about her identity.