系动词词义不完整,在句中不能单独使用（除省略句外）,后面必须接有表语,系动词和表语一起构成合成谓语.
一、系动词的分类：
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.
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.
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）
She is often the first to come here.（数词）
She is pretty and wise.（形容词）
The news was surprising.（分词）
His job is teaching English.（动名词）
The only method is to give the child more help.（不定式）
I must be off now.（副词）
The bridge is under construction.（介词短语）
That would be a great weight off my mind.（词组）
This is why he was late.（从句）
二、系动词的使用特点：
1.所有的系动词都可接形容词作表语,此处略举数例.
Our future will be beautiful.
She looks unhappy today.
Do you feel cold?
You seem/appear ill.
The food tastes delicious.
The weather is turning/ growing/ becoming/ getting cold.
He often went hungry.
2.能用名词作表语的系动词有：be,become,turn sound,remain,seem等.
He was a postman six years ago.
He has become a famous doctor.
He turned traiter to his country.
That sounds a good idea.
He remains an ordinary worker.
He seems a stranger to me.
3.能用不定式作表语的系动词有：appear,seem,get,prove,remain,turn out等.
She appears/ seems to be very young.
He appears/ seems to have caught cold.
They got to be friends.
The meeting turned out to be successful.
The theory proved to be right.
Much remains to be done.
4.能接从句的有：be,seem,appear,sound,look等.
That”s why he fell ill.
My idea is that we should help him.
It seems/ appears to me that something is wrong.
It sounds to me as if someone were trying to get into the house.
Your voice sounds as if you had a cold.
It looks as if it is going to rain.
5.能接介词短语的有：be,feel,look,sound,taste,remain等.
be是特别活跃的系动词,其后可接很多介词短语作表语.
He is at home/ in the library/ on the way home/ on holiday.
The police are after him.
He is at work on a new invention.
He found the girl was in tears.
They are on duty/ on strike/ on leave.
The road is under repair.
其他系动词能和介词搭配的范围很小.如：
It feels like a rain.
It looks like a rain.
It sounds like a train going under my room.
It tastes of apples.（这有苹果的味道.）
The concert remains in my memory.
6.能接分词的系动词有：be,become,get,grow,seem,appear等.
His report was surpring/ disappointing/ delighting/ moving/ astonishing…
The boy was moved/ delighted/ surprised/ disappointed/ astonished.
He has become/ got/ grown/ interested in modern physics.
He seems/ appears drunk.
系动词后还可接代词、数词、动名词、副词及其词组,基本都是be的用法.其他系动词几乎不能这样用或很少这样用,这里就不再赘述了.