连词是一种虚词， 它不能独立担任句子成分而只起连接词与词，短语与短语以及句与句的作用。连词主要可分为两类：并列连词和从属连词。并列连词用来连接平行的词、词组和分句。如：and, but, or, nor, so, therefore, yet, however, for, hence, as well as, both…and, not only…but also, either…or, neither…nor, (and)then 等等。

一、并列连词与并列结构
并列连词引导两个并列的句子。
1) and 与 or
判断改错：
( 错 ) They sat down and talk about something.
( 错 ) They started to dance and sang.
( 错 ) I saw two men sitting behind and whisper there.
( 对 ) They sat down and talked about something.
( 对 ) They started to dance and sing.
( 对 )I saw two men sitting behind and whispering there.
解析：
第一句： and 连接两个并列的谓语，所以 talk 应改为 talked 。
第二句： and 连接两个并列的动词不定式，第二个不定式往往省略 to ，因此 sang 应改为 sing 。
第三句： and 连接感观动词 saw 后面的用作的宾补的两个并列分词结构，因此 whisper 应改为 whispering 。
注意： and 还可以和祈使句或名词词组连用表示条件。（ or 也有此用法）
Make up your mind, and you'll get the chance.
= If you make up your mind, you'll get the chance.
One more effort, and you'll succeed.
= If you make one more effort, you'll succeed.
2) both …and 　两者都
She plays (both) the piano and the guitar.
3) not only…but (also), as well as 不但 … 而且）
She plays not only the piano, but (also) the guitar.
注意： not only… but also 关联两个分句时，一个分句因有否定词 not 而必须倒装。
Not only does he like reading stories, but also he can even write some.
4) neithe…nor 意思为 " 既不 …… 也不 ……" 谓语动词采用就近原则，与 nor 后的词保持一致。
Neither you nor he is to blame.

二、比较 and 和 or
) 并列结构中， or 通常用于否定句， and 用于肯定句。
2) 但有时 and 也可用于否定句。请注意其不同特点：
There is no air or water in the moon.
There is no air and no water on the moon.
　 在否定中并列结构用 or 连接，但含有两个否定词的句子实际被看作是肯定结构，因此要用 and 。
典型例题
---I don't like chicken ___ fish.
---I don't like chicken, ___ I like fish very much.
A. and ； and B. and ； but C. or ； but D. or ； and
　 答案 C 。否定句中表并列用 or, but 表转折。
判断改错：
( 错 ) We will die without air and water.
( 错 ) We can't live without air or water.
( 对 ) We will die without air or water.
( 对 ) We can't live without air and water.