1） as, (just) as…so…引导的方式状语从句通常位于主句后，但在(just) as…so…结构中位于句首，这时as从句带有比喻的含义，意思是"正如…"，"就像"，多用于正式文体，例如：
Always do to the others as you would be done by.
你希望人家怎样待你，你就要怎样待人。
As water is to fish, so air is to man.
我们离不开空气，犹如鱼儿离不开水。
Just as we sweep our rooms, so we should sweep backward ideas from our minds.
正如打扫房屋一样，我们也要扫除我们头脑中落后的东西。
2） as if, as though
两者的意义和用法相同，引出的状语从句谓语多用虚拟语气，表示与事实相反，有时也用陈述语气，表示所说情况是事实或实现的可能性较大。汉译常作"仿佛……似的"，"好像……似的"，例如：
They completely ignore these facts as if (as though) they never existed.
他们完全忽略了这些事实，就仿佛它不存在似的。（与事实相反，谓语用虚拟语气。）
He looks as if (as though) he had been hit by lighting.
他那样子就像被雷击了似的。（与事实相反，谓语用虚拟语气。）
It looks as if the weather may pick up very soon.
看来天气很快就会好起来。（实现的可能性较大，谓语用陈述语气。）
说明：as if / as though也可以引导一个分词短语、不定式短语或无动词短语，例如：
He stared at me as if seeing me for first time.
他目不转睛地看着我，就像第一次看见我似的。
He cleared his throat as if to say something.
他清了清嗓子，像要说什么似的。
The waves dashed on the rocks as if in anger.
波涛冲击着岩石，好像很愤怒。
