An appositive is a word, phrase or clause which is placed directly next to a preceding noun or pronoun and which renames or explains that noun or pronoun.

Examples:

My friend Henry won the prize, a two-year scholarship.

The belief that there will be nuclear war is widespread.

The idea that computers will recognize human voices surprises many people.

The possibility that the majority of the labor force will work at home is often discussed.

同位语从句的特点是由一个抽象名词+that从句构成，引导词一般是that, 而且that在从句中不充当任何成分。这些抽象名词有：news, idea, fact, doubt, evidence, promise, rumor, hope, truth, belief, message等，同位语从句是对抽象名词进行说明解释。

1. The news that our football team at last defeated Korea made the fans wild with joy. c.f.: The news that made the fans wild with joy was from the radio.

2. There is much evidence that the crime rate in this city is on the rise.

3. Einstein came to the conclusion that the maximum speed possible in the universe is that of light. 爱因斯坦得出的结论是宇宙中最大速度是光速。 　　　　　　　　　　　　　同位语从句

1. 从属连词that、whether引导的同位语从句。

He has the hope that he will become a college student. 他有上大学这么个愿望。

The question whether he should do this troubled him. 是否该做这件事这一问题使他很烦恼。

注意：由连接词that （一般不可省略） 引导的同位语从句，在句子结构上与关系代词that引导的定语从句有相似之处，但有区别：

1) The news that he had landed on the moon spread all over the country. 他登上月球的消息传遍全国。

2）The news that John told us interested all of us.他告诉我们的消息使大家都感趣。

解析：1）句中that从句中本身的内容就是"news "内容本身，that在句子中不充当任何成分，起连接作用，所以，本句中的that从句 是同位语从句；而2）句中that从句说明" news "是怎样获得的，不涉及"news"的内容， that从句中充当 "tell"的宾语，所以，本句中的that从句 是定语从句。另外，可带同位语从句的名词主要是少数一些可加入具体内容的表示信息、思想等概念的名词，如：fact，news，idea，truth，belief，doubt，hope，possibility，order，wish，message，promise，suggestion，report，reply，problem, question, thought等。

2. 连接副词how，when，where等引导的同位语从句。

You have no idea how worried I was！你不知道我是多么着急。