原因从句

　 主要由下列从属连词引导：

　 1． Because, as, since。其中 because 语气最强，表示直接、主要原因，通常引导的从句放在句尾，特别是回答 why 提出的　　　问题只能用 because; as 和 since 表示明显的、已知的原因，since 比 as 正式，如：
　　　　　They had to move because their building was to be pulled down.
　　　　　As Mary was the eldest, she looked after the others.
　　　　　Since they live near the sea, they often go sailing.

　　2． now that, seeing (that), considering (that), in that。这些连词与 as, since 意思相近，通常用于书面语，并且它们　　　兼有其它意义。now that 有“时间”含义，表示“既然”，说明一种新情况；seeing (that) 和 considering (that) 有“条　　　件”含义；in that 有“某一方面”含义，如：
　　　　　Now that you are well again you can travel.
　　　　　Seeing (that) they are just beginners, they are doing quite a good job.
　　　　　I was lucky in that I was able to find a good baby-sitter（保姆）.

　　结果从句

　 常用 so that, so ... that, such ... that, that 等连词引导，如：
　　　　I was caught in a shower, so that all my clothes got wet.
　　　　I was so tired that I could hardly keep my eyes open.
　　　　He was such a good runner that I couldn't catch him.

　　目的从句

　 常用 so that, in order (that), lest, for fear that 等连词引导，如：
　　　　I took a taxi so that I could be in time for the meeting.
　　　　Come closer in order that you may see the blackboard better.

　　so that 既可引导结果从句也可引导目的从句，但结果从句表示事实，通常不含情态动词；目的从句表示希望或想要实现的事实　　，通常含有情态动词，如：
　　　　He got up early so that he caught the train.（结果）
　　　　He got up early so that he could (might) catch the train.（目的）

　　Lest 和 for fear (that) 含有否定意义，并且从句中动词须用 “动词原形”或 “should + V.” 的虚拟语气，如：
　　　　He ran away lest he (should) be caught.
　　　　(= He ran away in order that he would not be caught.)
　　　　I checked all the results time and again for fear that there should be any mistakes.
　　　　(= I checked all the results time and again so that there wouldn't be any mistakes.)