连词是一种虚词，不能独立担任句子成分，只起连接词与词、短语与短语以及句子与句子的作用。连词一般分为并列连词和从属连词。除了连词外，许多连接代词、连接副词、关系代词和关系副词都可以用来引起一个从句。还有一些副词，如anyway，therefore，also，still等也有类似的作用。另外，有些词组，如:ontheotherhand，forthatreason等也可以帮助前后文更加连贯。考生在准备连词时应注意以下几个问题。
1.连接两个分句，一个连词就够了。容易出错的典型例子是：
Al though he was tired，but he went to work.
Be cause she liked him，so she went out with him.
在上面所提到的两个例子中，我们可以选用although或but，because或so，不能
同时使用两个连词。但是连接三个分句时，可以用两个连词。如：
Al though he was tired，he went to work，but he didn‘t stay there long.
类似的错误还有把that和where，how或whether连在一起用。如：
I asked him that how he was working.
L wondered that where he lived.
2.关系代词who，whom和which的一个特殊用法是可以连接分句。所以它们既是代词，又是连词。容易出错的典型例子是：
He never listens to the advice which I give it to her.
在该句中it是多余的，which连接两个分句，同时又代替it而成为第二个分句的宾语。
3.That经常用来代替which和who，但是不常用that来代替where和when。容易
出错的典型例子是:
The house that she lives is very small.
正确的句子应该是：
The house where she lives is very small.
The house that she lives in is very small.
4.连词不能单独和一个分句连用。连接词要连接两个分句，而这两个分句一般要
写成一句话，即不能写成中间用句号隔开的两个独立的句子。容易出错的典型例子是：
When I came back home.It was late.
正确的句子应该是：
When I came back home it was late.