连系动词多有自己的意思，但不能独立作谓语，必须与表语（名词、形容词，或与之相当的词类、短语、从句）一起构成合成谓语。最常用的连系动词为be（是）动词，即完全连系动词，另外还有look, turn, feel, get, become, sound, smell, stand, go, remain等半连系动词。无论是完全连系动词还是半连系动词、后面都有表语。由于半连系动词是由实意动词变来的，那如何分辨该动词为实意动词还是半连系动词呢？这对初学英语的中学生来说会感到有点困难，我在教学中尝试用比较法和替换法，使学生较能接受。
1．比较法
比较下列各组句子
(1) A． Please look at the blackboard．请看黑板。
B． He looked a perfect fool．他看上去是个十足的傻瓜。
(2) A． Turn to Page 16．翻到 16页。
B． He turned traitor to his country．他背叛了祖国。
A． He felt it his duty to help others． 他认为帮助别人是自己的责任。
B． I felt very hungry after a long walk． 走了一段长路，我感到很饿。
A. Get me some ink．给我一些墨水。
B． Our motherland is getting stronger and stronger． 我们国家变得越来越强大了。
A． Such words do not become a scholar． 那样的话不像出自学者之口。
B． Some of the land became covered with water． 一些田地覆盖着水。
A． This black key on the piano won't sound． 这钢琴上的黑键按下去不响。
B． The story sounds interesting． 这故事听起来很有趣。
A. I am sure I smell gas．我肯定闻到了煤气味。
B. The flowers smell sweet．花朵散发芳香。
A. He was too weak to stand．他太虚弱，不能站立。
B. Holding the note in his hand, he stood there dumbfounded．他拿着钞票，站在那里，目瞪口呆。
A. He goes to school early every morning. 他每天早上很早上学。
B. They went mad．他们发狂了。
A． I remained 3 weeks in Paris． 我在巴黎逗留了三周。
B. He never remained satisfied with his success．他从不满足于自己的成绩。
2．替换法
分析以上10组句子我们不难看出B组斜体动词均为连系动词，因为如果我们把动词 be（是）的适当形式替代斜体动词，句子能够成立，后面的成分即是表语。
（1）He was a perfect fool．
（2）He was a traitor to his country.
（3）I was very hungry after a long walk．
（4）Our motherland is stronger and stronger．
（5）Some of the land was covered with water．
（6）The story is interesting．
（7）The flowers are sweet．
（8）Holding the note in his hand, he was there dumbfounded．
（9）They were mad．
（10）He was never satisfied with his success．
反之，如果把 be（是）动词的适当形式替代 A组斜体动词，句子则不能成立，无法解释，A组动词均不为连系动词：
*（l）Please be at the blackboard．
*（2）Be to Pagel6．
*（3）He was if his duty to help others．
*（4）Be me some ink．
*（5）Such words are not a scholar．
*（6）The black key on the piano won't be．
*（7）I am sure I am gas．
*（8）He was too weak to be．
*（9）He is to school early every morning．
*（10）I was 3 weeks in Paris．
另外半连系动词是由实意动词变来的。所以把含有半连系动词的句子改为疑问句时，一定要用助动词。
例如：1． Do they look tired？
2．Has she got ready？
3．Did it become much more expensive to travel abroad？
不论完全连系动词或半连系动词，它们都有时态的变化，但有些半连系动词从形式上看像是现在进行时，实际上并不表示动作正在进行。而是表示“渐渐”的意思或表示一种感情色彩。
（1）It's getting warmer and warmer．天渐渐暖和起来了。
（2）Are you feeling better now？你现在好点了吗？
因为半连系动词本属于不及物动词，所以没有被动语态。
如不能说：* Good medicine is tasted bitter to the mouth．应说：
Good medicine tastes bitter to the mouth．良药苦口。
半连系动词的教学还是个较困难的问题，但在初学阶段用先比较，再替换的方法，还是能使学生