英语的同位语
同位语是一个名词或代词，在另一个名词或代词的旁边用于解释或识别这个对象。下面是一些例子：
Your friend Bill is in trouble.
My brother's car, a sporty red convertible with bucket seats, is the envy of my friends
Timothy, their youngest child, is very musical.
The American author Ernest Hemingway spent many years abroad.
上面四个句子中的主语用的蓝色字体，补充说明它们的红色单词就是同位语。
在语法上，同位语可以是一个单词，一个短语或者是一个从句来说明另一个单词. 名词从句也可以起同位语的功能。例如：
I think the solution, that he hired a replacement, was the best course of action at the time.
The problem, that you did not pick up the packages, delays the entire product schedule.
The answer from the company, that we buy a new table, angers me.
My decision, for you to leave the day after us, stands.
His choice, for her to bring the kids the week after, seems logical.
Your idea, for Olive to make more pickles, appears ill-conceived.
判断是否是同位语从句，就看将其去掉是否影响整个句子的意思。下面这个句子that 引导的句子非常像evidence的同位语，但that smoking can lead to many diseases仍然是个定语从句，用来限定evidence。
Modern science has given clear evidence that smoking can lead to many diseases.
而同位语是可以去掉，不影响主句的使用。
Lucy and Lily, who are twins, are strong swimmers.
这里who are twins是同位语，去掉不影响主句。
由此可见同位语从句是非必须的，不像定语从句去掉影响表达。注意同位语从句前后有两个逗号，这一点有点像非限定性定语从句，但它还是与其有差别的，看下列例句：
Their mother, who never learned to swim herself, had them take swimming lessons when they were young.
这里划线部分是非限定性定语从句。
阅读下列同位语的例句，都是说明入侵者intruder是个蟑螂，从单词到词组，最后到同位语。
The intruder, a cockroach, is crawling across the kitchen table.
The intruder, a large, inquisitive cockroach, is crawling across the kitchen table.
The intruder, a large, inquisitive cockroach with hairy legs, is crawling across the kitchen table.
The intruder, a large, inquisitive, hairy-legged cockroach that has spied my bowl of oatmeal, is crawling across the kitchen table.
