一.主语补足语即被动语态中的宾语补足语.
eg.They caught boy stealing.
被动语态 The boy was caught stealing.
stealing 即为主语补足语
被动语态后的主语补足语
二.主语补足语的判别
1.看句中的动词是不是可接复合宾语,而且是不是被动语态,与此同时还要看其后部分的逻辑主语是不是句子的主语.
2.另一种最简单的方法是：如果还不能看出来就可以把全句改成主动语态,加上一个主语we或people等.改成主动语态后,看后面是不是变成了“宾语+宾语补足语”了,这样我们就可以判别原句后面是不是主语补足语.
e.g.被动句：She was found reading in the library.(主语补足语) 主动句：We found her reading in the library.(宾语+宾语补足语)
三.主语补足语形式种种
1.动词elect,call,name,make,find,leave等后面常接名词用作主语补足语.例如：① The dog is called Karl.② Coal is sometimes called stored-up sunlight.③ He was found the right man for the job.
2.动词keep,make,paint,cut,burn,beat,wash,find,consider,wipe等后面常接形容词用作主语补足语.例如：① The door was painted white.② The old man was found weak.③ The classroom is always kept clean every day.
3.动词see,watch,hear,feel,listen to,look at,imagine等后面接分词用作主语补足语.例如：① He is often heard reading English.② The professor was seen making an experiment in the chemistry lab.③ The glass was found broken.④ The classroom was found crowded with people.
4.感官动词see,watch,hear,notice,feel,make等后面接带to的不定式用作主语补足语.例如：① He was seen to come upstairs.② Ice is known to be in a solid state.③ The spy was ordered to be hanged.
5.介词短语用作主语补足语.例如：① The books in the study must be kept in good order.② He was found in good health.③ English is considered of great importance for us.
6.as后面接名词、形容词、分词等用作主语补足语.例如：① English is taken as a useful means for research work.② The news is considered as true.③ The stool is usually thought as having four legs ④ The vase is thought as broken.
7.由what引导的名词性从句用作主语补足语.例如：The boy has been made what he is.