(2). 当as引导的定语从句位于具有否定意义的主句之后时，as从句所修饰的范围不包括否定意义。例如：

Spiders are not insects, as many people think. = Spiders are not insects. But many people think they are. 许多人认为蜘蛛是昆虫，但蜘蛛并不是昆虫。

(3). 当as引导的定语从句位于具有否定意义的主句中间时，as从句所修饰的范围也不包括否定意义。例如：

She did not, as her friend had feared, open the case. 她没有打开盒子，而她的朋友就是怕她当面打开盒子。

注意2: 当修饰句子的非限制性定语从句位于句尾时，as可以用which来替代。例如：

I live a long way from work, as (which) you know. 我住得离工作单位很远，这你是知道的。

但是，当as从句位于句首或句中是，as就不能用which来替代了。例如：

As you will find out, I will never let you down. 你将会发现，我绝不会使你失望的。

Taiwan is, as you know, an inseparable part of China. 你们知道，台湾是中国不可分割的一部分。

此外，如果主句为否定句，则位于句末和句中的as从句所修饰的范围并不包括主句的否定意义，此时，as也不能用while来替代。例如：

Greenland was not a continent, as people thought. 格陵兰并不像人们所想象的那样是一个大陆。

四、作介词，

1. 表示 “好像(某人)”，例如:

They entered the building disguised as cleaners. 他们化装成清洁工人的模样进入大楼。

2. 表示“作为，当作”，例如：

I found a job as a teacher. 我找了一份教师的工作。

3. 表示“当某人是(某身份)时。例如：

As a child, she was sent to three different countries. 她儿时去过三个不同的国家。

4. 表示“因某人是(某身份)”，例如：

As her private secretary he has access to all her correspondence. 他是她的私人秘书，能接触到她所有的信件。

注意1：as引导的介词短语大多用作状语，as译为"作为"，少数情况可引起宾语补足语。例如:

As a Party member, I'll take the lead in everything. (状语)

She works as a nurse. (状语)

Tom has me as one of his best friends. (引起宾语补足语)

注意2：as和like都可以作介词，但意义不同。as表示“以实际的身份或地位”。 like则表示“与…相似，以与…相类似的方式”。例如：

(1). He spoke as a teacher.

(2). He spoke like a teacher.

句(1)的意思是：“他作为老师发言”或“他以老师的身份发言”。句(2)的意思是：“他讲话很像是老师”。

五、用于一些固定搭配

1. as good as差不多，几乎

Don’t worry, the matter’s as good as settled. 别担心，问题差不多已经解决了。

When the car was repaired, it looked as good as new. 这辆汽车修理好的时候，看起来差不多就像新的一样。

2. as if /as though 似乎;好像

He behaved as if nothing had happened. 他装着若无其事的样子。

She treats him as though he was her own son. 她待他好像待自己的儿子一样。

另外，as if可以接一个动词不定式短语。例如：

He waved his hand to me as if to have something to tell me. 他向我挥手好像有什么要告诉我。

3. as well as 同(一样也);和;还

Joan can speak Chinese as well as English. 琼能讲英语还能讲汉语。

He spent all his money, as well as wasting his time. 他不仅浪费了时间，还花光了他所有的钱。

4. such...as, such as 像……这样的

I bought a lot of fruits, such as apples, oranges, bananas and so on. 我买了许多种水果，像苹果，桔子，香蕉等。

We had such books as you never saw. 我们有一些你从未看过的书。

5. as for 至于某人(某事物)

We had a delightful weekend in the country. As for the traffic, we had no difficulty. 在乡下我们度过了一个愉快的周末。至于交通，我们没遇到任何困难。