(2) seem, appear, prove, continue, turn out, get, grow, come 等连系动词后也可接不定式(尤其是to be)作表语：
She always seems to be sad. 她常常显得很忧伤。
My advice proved to be wrong. 我的意见证明是错的。
She appears to have many friends. 他好像有很多朋友。
The weather turned out to be fine. 天气结果很好。
Circumstances continue to be favorable. 情况仍然是有利的。
He has grown to like studying English. 他渐渐喜欢学英语了。
【注】若所接不定式为to be，通常可以省略。不过，若其后接的是表语形容词，则to be通常不宜省略。另外，连系动词look后能否接to be似乎尚有争论，不过，在现代英语中接to be的现象已较普遍。
(3) sound, smell, feel, taste, become等连系动词后通常不能接不定式：
误：These oranges taste to be good. (应去掉to be)
误：The roses smell to be nice. (应去掉to be)
(4) 有的连系动词后接的从句可用不定式来改写：
It seems that she’s right. / She seems to be right. 她似乎是对的。
It appears that you have made a mistake. / You appear to have made a mistake. 似乎你弄错了。