主語(yǔ)修飾語(yǔ)的第三種用法是用作主語(yǔ)的補(bǔ)語(yǔ).
它用在系動(dòng)詞后,是句子的一個(gè)基本成分.它和限制性定語(yǔ)、解釋性定語(yǔ)不同,后面兩者為從屬成分,去掉后不影響句子結(jié)構(gòu).由于主語(yǔ)補(bǔ)語(yǔ)在前面已作詳細(xì)討論（詳見(jiàn)1438-1486）,這里僅舉少量例子：
He is kind．He seems afraid．John got rich．（形容詞）
He appeared tired．Mary became intoxicated．My brother remained unmarried．（過(guò)去分詞）
It looks interesting．The story is amusing．The news was shocking．（現(xiàn)在分詞）
Dinner is over．The show is on．The time is up．（地點(diǎn)副詞）
I feel at home． He seems in debt． He appears out of humour．（介詞短語(yǔ)）
He is to die at eighty．The sample is not to be sold．
This book is to be read ten times．（不定式）