连词用于引导从句以形成句子的一部分或修饰句子的构成要素的叫作从属连词.由从属连词所引导的句子叫从句。
连词是连接单词,短语,从句或句子的一种虚词.从属连词这种连词是用以引导名词性从句和状语从句的.在英语词类中，连接词可说是最容易掌握的一种。从结构上说，英语连接词分两大类：并列连词（coordinating conjunctions）和从属连词（subordinating conjunctions）。并列连词连接两个或两个以上地位平等的字、词组或分句。例如：(1) Air and water are indispensable to me.(2) She likes going out with friends or playing outdoor games.(3) Most workers have a good income, so they look very happy.从属连词连接两个或两个以上的分句，形成复杂句中的从属分句。例如：(4) He said that he did not want to go .(5) Many things have happened since I last saw him.(6) You may come if you want to.上述连词的用法，看起来不难，但错误也难免。下面是些好例子：(1) This book may be used both as a text as well as a reference book.这里的“as well as”和“both”不能搭配，应该将“as well ”改为“and”，使“both.......and......”变成关联连词（ correlative conjunction）(2) He not only speaks Mandarin but also English.这里的“not only”应该移到“speaks”后面，使这个动词兼顾两个等立宾语：“Mandarin”和“English”。
（3） Although he is fat, but he is very weak.英语里的“although”和“but”是不见面的 ，因此这句里的“ but”要去掉，不然“although”就要出来。
（4） Jim is not so strong like you.这里的“not so”必须和“as”连成一体；介词“like”是不适宜的。
（5） No sooner had we reached our destination, they left."No sooner"必须和"than" 配成关联连词，把"than" 省掉是不对的，应该补上：No sooner had we reached our destination than they left.这句子的意思也可透过“as soon as”反映出来：“As soon as we reached our destination, they left.”(6) I took a taxi and which took me to the station.这里的并列连词“and”是多余的，必须去掉。如果要保留“and ”也可，但是形容词分句里的关系代词“Which”要改成主语“it” ，使整个句子变成并列分句如下：I took a taxi and it took me to the station.(7) My friend came up to me and held my hand, said good-bye excitedly.这里的“and”应该用来连接最后两个谓语才对：My friend came up to me, held my hand, and said good-bye excitedly.不然，就要把“said”改成“saying”。My friend came up to me and held my hand, saying good-bye excitedly.
