副词从句由完整的简单句外加有意义、表达逻辑关系的连接词（because、if、although等）构成，它附在一个完整的主要从句中作修饰语，两个从句的关系类似对等从句。
一、副词从句与对等从句的比较
[副词从句]：Because he needs the money， he works hard.
[对等从句]：He needs the money, and he works hard.
副词从句He needs the money和主要从句he works hard都是完整且独立的句子，以because连接起来。这一点和对等从句一样，只是对等从句使用的是对等连接词and。在解释上副词从句有明显的从属关系，而对等从句则没有。
二、副词从句与名词从句的比较
[名词从句]：The witness said that he saw the whole thing.
[副词从句]：The witness said this, though he didn't really see it.
区别：副词从句的连接词不同于名词从句的that，是有意义的，比如though表示让步，另外一点副词从句是修饰语的词类，在一个完整的主要从句中作修饰语。
三、副词从句的种类
① 时间、地方（after、until、when、where等）
He became more frugal after he got married.
after后的从句修饰动词became的时间。
I'll be waiting for you until you're married.
until后的从句修饰will be waiting的时间，未来时间的副词从句中虽然事情还未发生，但是要使用现在时态表示到了那个时候来说。
② 条件
If he calls, I'll say you're sleeping.
主句中的will say是在副词从句if引导的he calls条件下产生的，在表示条件的副词从句中，如果主句是未来时间，那么副词从句仍然要使用现在时表达当作真正发生。同时，主句中的you're sleeping也要用现在式，表达在睡觉的意思。
Suppose you were ill, where would you go?
副词从句you were ill修饰动词would go。
③ 原因，结果
As there isn't much time left, we might as well call it a day.
as连接词引导的副词从句，修饰动词might call的原因。
There's nothing to worry about, now that father is back.
now that连接词是由now配合that形成的，解释为“既然”，不能当作名词从句使用。
He looked so sincere that no one doubted his story.
so……that……表示因果关系，所以是副词从句。
④ 目的
The mother locked away the drugs so that the kids wouldn't swallow any by mistake.
I've typed out the main points in boldface, in order that you won't miss them.
I've underlined the key points, lest you miss them（以免）
You'd better bring more money, in case you should need it.（万一）
⑤ 让步
Although you may object, I must give it a try.（虽然）
While the disease is not fatal, it can be very dangerous.（虽然）
Wh-拼法的连接词（whether、whoever、whichever、however、wherever、whenever）
Whether you agree or not, I want to give it a try.
Whoever calls, I won't answer.
⑥ 限制
As far as money is concerned, you needn't worry.
Picasso was a revolutionary in that he broke all traditions
注：in that 是in the sense that的简化
⑦ 方法、状态
He played the piano as Horowitz would have.
He writes as if he is left handed.
He writes as if he were left handed.
He writes as if he was left handed.
以上三句中，is表示应该是左撇子；were表示不是，只是冒充左撇子；was表示可能是左撇子。要注意区分。
