一、条件状语从句条件状语从句表示主句谓语动词的行为发生的条件，通常由if，unless(除非) ，so long as(只要)等连词引导。

We'll go to the Great Wall if it is fine tomorrow.如果明天天气好，我们就去长城。Unless the policy is changed，the future is indeed dark.除非这政策改变，否则前景实在黑暗。As long as I have anything，you will always have a home.只要我有的话，你总会有家可住的。真实条件状语从句用直陈语气，其他关联词有：suppose，supposing(that)，assuming(that)，providing(that) ，provided(that) ，in the event(that) ，given(that)，just so(that)，on condition(that) ，as far as，in case等。Suppose/Supposing we can't get the necessary equipment，what shall we do 假设我们弄不到必要的设备，那我们怎么办 He is an honest man as far as I know.据我所知，他是个诚实的人。In case the house burns down， we'll get the insurance money.万一这房子烧毁了，我们会获得保险金的。

二、目的状语从句目的状语从句表示目的。常用关联词有：so，so that，in order that，for fear(that)，lest(以免)等。He arranged everything so that we could get there at one o'clock.他安排好了一切，以便我们能一点钟到达那里。I'll rig him up at once so he shouldn't wait for me.我马上给他打电话，让他别等我了。He arrived early in order that he might not miss the report他到得很早，为的是不错过那个报告。They didn't talk much for fear(that) others might hear them.他们没说太多，生怕别人听见了。