一、目的状语从句的定义：从句部分是用以补充说明主句中谓语动词发生的目的的状语从句。表示目的状语的从句可以由that, so that, in order that, lest, for fear that, in case等词引导；
目的状语从句的谓语常含有may, might, can, could, should, will, would等情态动词。
二、目的状语从句用法：
(一) so that 表示“为了；以便”。
例如:①We turned on the light so that we might see what it was.我们把灯打开，以便看看它是什么。
②They put a screen around his bed so that the doctor could examine him.他们在他床的四周放上屏风，以便医生给他检查。
注意：
1、so that有时可以省略so，直接用that连接。例如:Bring it closer(so) that I may see it better. 把它拿近点儿，让我看看仔细。
2、当主从句的主语一致时，so that引导的状语从句可以改为短语结构so as to do。
例如:从句: We made a strategic withdrawal, so that we could build up ourforces for a renewed attack. 我们作了一次战略性退却，以便我们能积蓄力量再次进攻。=We made a strategic withdrawal, so as to build up our forces for arenewed attack.
3.so that也可以表示结果，意思为“因此；所以”。此时，其从句的谓语动词中一般不使用情态动词。
例如:①Everyone lent a hand, so that the sowing was done in time. 每个人都帮了忙，所以播种才得以及时完成。
②I took no notice of him, so that he flew into a rage. 我没注意到他，他因此勃然大怒。
4、注意so that与so...that的区别。
例如:
结果状语从句：He stayed up so late last night that he couldn't get up early this morning.他昨晚熬夜太晚，以至于今早无法这么早起床了。
目的状语从句：He went to bed very early last night so that he could get upearly this morning.他做完很早就睡了，以便今早能够早起。
(二) in order that 表示“为了；以便”。
例如:①I am saving money in order that I can buy a house.我正在攒钱，以便我能买一所房子。
②In order that we might get there on time, we should set out early.为了及时赶到那里，我们应该早些出发。
注意：当主从句的主语一致时，in order that连接的从句可以改为短语结构in order to do。
例如: I came in order that I could see Jack.我来，是为了能见到杰克。
(三) for fear that 表示“以免；唯恐”。此时，其从句中的谓语动词如果采用的情态动词是should时， should可以省略。
例如: ①He told us to keep quiet for fear that we might disturb others.他让我们保持安静，以免打扰别人。
②We hurried along for fear that we (should) be late.我们赶着往前走，唯恐会迟到。
注意：
1、当主从句的主语一致时，for fear that 的从句结构可以改为for fear of的短语结构。
例如: We spoke quietly for fear that we should wake the guards.我们悄悄说话，以免惊醒警卫。=We spoke quietly for fear of waking the guards.
2、当主从句的主语不一致时，for fear that的从句结构也可以改为短语结构。
例如:She took up the meter with care for fear that it (should) be damaged. 她小心拿起量表，以免它受到损害。=She took up the meter with care for fear of its being damaged.
(四) lest 表示“惟恐；以免”。此时，其引导的从句的谓语动词中使用的情态动词一般都是should , should可以省略，这也是虚拟语气的一种。
例如: ①They spoke in whispers lest they (should) be heard.他们低声说话，唯恐被别人听见。
②He took a flashlight lest it (should) get dark before he returned. 为了预防回来以前天就黑了，所以他带着手电筒。
注意：
lest 一般只用于书面语中。例如: She drew in her breath lest he should hear it now.她吸了口气，唯恐他现在听见了。
(五) in case 表示“万一；以防”。此时，其引导的从句的谓语动词一般都会采用情态动词should, should可以省略，这是虚拟语气的一种。
例如: ①They watched him closely in case he (should) escape.他们严密监视他，惟恐他会逃脱。
②I stopped suddenly in case he (should) think that I was showing off.我突然停住，唯恐他会认为我是在炫耀。
注意：
1、in case引导的从句中的谓语动词也有可能用其他情态动词。
例如: I'll sit up for a time, in case I may be wanted.我先不睡，说不定会通知得着我。
2、当in case表示“如果;假如”时，其引导的从句不再使用虚拟语气，也大多不再使用情态动词。
例如:①In case she comes back, let me know immediately.假使她回来了,立刻告诉我。
②I keep a warm coat at work in case it suddenly turns cold. 上班时我总带件温暖的上衣，以防天气突然变冷。
3、注意in case of的用法，表示“假如；如果发生”。
例如:①In case of fire, ring the alarm bell.如遇失火，请按警铃。
②We have an auxiliary generator in case of power cuts.我们有一台万一断电时使用的备用发电机。