常见的系动词大致可分为三类.
第一类：表示特征或状态的,有be,look,feel,seem,appear,smell,taste,sound,turn,out（结果是、证明是）等.
You”ll be all right soon.
You don”t look very well.
I feel rather cold.
He seems to be ill.
It appears that he is unhappy.
第二类：表示从一种状态到另一种状态的变化,有become,get,grow,turn,fall,go,come,run等.
He became a world-famous scientist.
It is getting warmer and warmer.
It grew dark.
The food has turned bad.
Yesterday he suddenly fell ill.
第三类：表示保持状态的,有keep,remain,continue等.
Keep quiet,children!
The weather continued fine for a long time.
It remains to be proved.
系动词后的表语可以是名词、代词、数词、形容词、分词、动名词、不定式、副词、介词短语、词组、从句,系动词be可用于上述所有情况.如：
The pepople are the real heroes.（名词）
That”s something we have always to keep in mind.（代词）