主语修饰语的第三种用法是用作主语的补语.
它用在系动词后,是句子的一个基本成分.它和限制性定语、解释性定语不同,后面两者为从属成分,去掉后不影响句子结构.由于主语补语在前面已作详细讨论（详见1438-1486）,这里仅举少量例子：
He is kind．He seems afraid．John got rich．（形容词）
He appeared tired．Mary became intoxicated．My brother remained unmarried．（过去分词）
It looks interesting．The story is amusing．The news was shocking．（现在分词）
Dinner is over．The show is on．The time is up．（地点副词）
I feel at home． He seems in debt． He appears out of humour．（介词短语）
He is to die at eighty．The sample is not to be sold．
This book is to be read ten times．（不定式）