同位语从句的位置与定语从句的比较：
1、同位语从句与定语从句一样,都是用在名词后面.所不的就是：定语从句是修饰限制它前面的名词,因此,它是属于形容词从句.而同位语从句属于名词性从句,它是用来 .说明它前面的名词内容的,或者说是解释前面名词的内容.
2、同位语从句只用that作为开头（I have no idea除外）,属于连词,在从句中不起成分作用,但不可省略.而定语从句是以关系代词开头,关系代词在从句中起句子成分作用（作主语、宾语或表语）,作宾语时可以省略.
3、只有在内容方面可以进一步阐明的名词（一般为抽象名词）才能带同位语从句,而几乎任何名词都可以带定语从句.
比较：
(1)The suggestion (that) she has given at the meeting is good.
(2)The suggestion that she should stay in the room is good.
(1)句中that she has given at the meeting这个从句说明了是她提出的建议,不是别人的建议,也就是限定了the suggestion的范围,但并没有说明建议的内容.从结构上分析,that是give的宾语,所以这个从句是定语从句.
(2)句的that she should stay in the room这个从句说明了建议的内容,同时,that只起连词作用,在从句中既不是主语,也不是宾语,但不能省略,所以它是同位语从句.
二、同位语从句前常用的名词：
同位语从句说明的名词常见的有：ability, advice, answer,belief, doubt, discovery, fact, fear, hope, idea, information, message,news, order, possibility, problem, proposal, question, story, suggestion, theory, thought, word(消息)等.而不可说明的名词是不会接同位语从句的.比如：man, water, sun等具体的人或事物.例如：
There is no doubt that the prices of cars will go down.
The belief that the company will make a great is shared by everyone.
三、where, when, why, how, who, what等在引导同位语从句时,一般只用于I have no idea结构中,其实,这种类型的同位语从句应该列入宾语从句的范畴,因为I have no idea意思就是I don't know...
如：I have no idea where I should go.
I have no idea how I can get to the railway station.
四、有时候主句的谓语比较短,同位语从句比较长,这个从句就不一定紧接在它所说明的名词后面.如：
Word(消息) came that our Chinese women team had beaten Japanese.