连词不能在句中担任句子成分，而只起连接词与词(a)，短语与短语(b)以及句与句(c)的作用，如：
a. Are you going to have the contest today or tomorrow?
比赛是今天还是明天举行?
b. Do you have your coaching in the evening or in the afternoon?
你们的辅导是在晚上还是在下午?
c. Hurry up, or we'll be late.
赶快，否则我们就迟到了。
这里可以看出同一连词or，可以起三种不同的作用。有些连词，有时把自己所在的句子和前面的句子，在意思上连接起来，使前后文比较连贯，如：
At first she didn't want to go. Later, however, she changed her mind.
开始她不想去，但后来她改变了主意。
一般说来，连词在英语中运用还比较多，这是值得注意的。
连词可分为两类：
1.并列连词:用来连接平行的词、短语或分句。常见的并列连词有and, but, or, nor, so, therefore, get, however, nevertheless, for, hence, as well as, both...and, not only...but also, either...or, neither...nor, (and) then。
2.从属连词:用来引起一个从句在句中担任一个成分。常见的从属连词有after, when, before, as, while, since, until, till, although, though, if, even if, unless, lest, because, than, that, whether, so that, as soon as, as long as, in order that, as if, as though, suppose (that), provided (that), in case (that), on condition (that), now that, seeing that, so...that, such...that, as...as, so...as 等。
