一、用to do sth表目的
用不定式表目的是最简单也是最常用的方法，它既可以用于句末，也可用于句首，但比较而言，用于句首时，其强调意味较浓。如：
After missing a term through illness he had to work hard to catch up with the others. 他因病一学期未上课，得努力赶上其他同学。
To avoid any delay please phone your order direct. 为免延误，请直接打电话预订。
To keep themselves awake they sat on the floor and told each other stories. 为了不至于睡着，他们坐在地板上轮流着讲故事。
To avoid back problems， always bend your knees when you lift heavy objects. 为了不使背部受伤，你在扛重东西时，一定要将膝盖弯曲着。
不定式的否定式为not to do sth，而不是 to not do sth。如：
She had to struggle not to give in to a desire to laugh. 她极力控制自己不要笑出来。
Then there was the mad rush not to be late for school. 然后就是匆忙往学校赶，以免迟到。
I went to France not to study French， but to study architecture. 我去法国不是为了学法语，而是为了学建筑。
He claimed he had bought the cigarettes for home consumption， not to sell them. 他声称他买烟是为了自家享用，不是为了出售。
二、用so as to do sth表目的
so as to do sth是to do sth的变体，意思是“以便”“为了”“为的是”等。用so as to do sth表示目的时，它通常用于句末。如：
I left a message so as to be sure of contacting her. 我留下了张条子以便与她取得联系
The two lovers dropped back so as to be alone. 那对情人落在后面，为的是两人好单独在一起。
I always keep fruit in the fridge so as to keep insects off it. 我总是把水果放在冰箱里，以防虫子叮咬。
表示目的的so as to do sth有时也可放在句首（但是若so as to do sth是表示结果，则不可放在句首）。如：
So as to show his boss what a careful worker he was， he took extra trouble over the figures. 为了向老板显示他是个工作非常细心的人，他在这些数字上费了比平常更多的力气。
so as to do sth的否定式是so as not to do sth，意思是“为了不……”“以免”。如：
They tiptoed upstairs so as not to wake the baby. 他们踮着脚上楼，以免吵醒孩子。
We left in the daytime so as not to arouse suspicion. 我们在白天离开以免引起怀疑。
I shut the door quietly， so as not to wake the baby. 为了不惊醒宝宝，我轻轻地关上门。
三、用in order to do sth表目的
in order to do sth也是to do sth的变体。用in order to do sth表示目的时，它既可以用于句末，也可用于句首，但比较而言，用于句首时，其强调意味较浓。如：
She lied about her age in order to get the job. 她为了谋得那份工作隐瞒了年龄。
She arrived early in order to get a good seat. 她到得很早，图的是得个好座位。
Teamwork is required in order to achieve these aims. 完成这些目标需要团队合作。
In order to get the job you must be able to drive. 要做这项工作你得会开车。
In order to get into a good school， I must study even harder. 为了考入一个好的学校，我必须更加用功。
in order to do sth的否定式是in order not to do sth，意思是“为了不……”“以免”。如：
She slept in a separate room in order not to disturb him. 她在另一房间睡觉，为了不至打扰他。
Please reply at once in order not to lose this opportunity of a lower price. 请立即回复，以免失去这次低价的机会。
They must have worn gloves in order not to leave any fingerprints. 他们一定戴上了手套，以防留下指纹。
注意，in order to do sth 还有另外一个否定形式，那就是 not in order to do sth，其意为“不是为了……”。如：
Big farmers are moving in， not in order to farm， but in order to speculate with rising land prices. 大农场主正在不断涌进来，不是为了耕作，而是要利用不断上涨的地价进行投机。
This expression refers to encounters between ships of hostile nations. One ship might fire a shot at another， not in order to hit it， but to warn it to move. 这个表达源于敌对国船只在海上相遇时，一方可能向另一方鸣炮，不是为了击中目标，而是警告其快速离开。
四、用so that表目的
so as to和so that均可表示目的，两者的区别是，前者引出不定式，后者用以引导目的状语从句。与用so as to do sth表示目的的情形相似，so that引导的目的状语从句通常位于主句之后。如：
I will give him a key so that he can get into the house whenever he likes. 我会给他一把钥匙，好让他能随时进来。
I got here early so that we could have a few minutes alone together. 我到这儿早些是为了我们能单独在一起待几分钟。
They wrote the notices in several languages so that foreign tourists could understand them. 他们把通知用几国文字写出来，以便让各国游客都能看得懂。
有时可省略其中的that。如：
Leave the keys out so (that) I remember to take them with me. 把钥匙放在外面，好让我记得带。
I deliberately didn’t have lunch so (that) I would be hungry tonight. 我有意没吃午饭，为的就是让自己今晚能感到饿。
so that 引导的目的状语从句有时还可置于主句之前（但是，若so that引导的从句是表示结果，则不可放在句首）。如：
So that I shouldn’t worry， he phoned me on arrival. 为了不让我担心，他一到就给我打了电话。
So that I shouldn’t forget it， I made a knot in my handkerchief. 为了免得忘记，我将手帕打了一个结。
So that the coming generation can learn the martial arts， he has recently devoted much time to writing books on the subject. 为了下一代能够学会这些武术，他近来花了许多时间著书立说。
五、用in order that表目的
in order to和in order that均可表示目的，两者的区别是，前者引出不定式，后者用以引导目的状语从句。与用in order to do sth表示目的的情形相似，in order that引导的目的状语从句可以位于主句之前或之后。如：
We arrived early in order that we could get good seats. 我们到得早，以便找到好座位。
These men risk their lives in order that we may live more safely. 这些人甘冒生命危险，为的是让我们生活更安全。
I bought a new car in order that my wife might learn to drive. 我买了一辆新车，以便我妻子学习驾驶。
In order that you may create such a picture， you have to possess certain artistic weapons. 创作这样的画，你得具有某些艺术手段。
六、用in case表目的
in case用于引导目的状语从句时，意思是“以防”“以免”。如：
He took his umbrella in case it should rain. 他带上了雨伞，以防下雨。
You’d better take the keys in case I’m out. 你最好带上钥匙，以防我不在家。
Listen out for the baby in case she wakes up. 注意听宝宝的动静，她醒来好知道。
in case 引导的目的状语从句有时也可位于主句之前。如：
In case anyone was following me， I made an elaborate detour. 为了防止有人跟踪我，我特地绕了弯路。
注：也有人认为这样用的in case 从句为原因状语从句，意思是“因为怕……”。比较：
I had a snack， just in case there was no time to eat later. 我吃了些点心，以防过会儿没有时间吃饭。（将in case译成“以防”，将之视为目的状语从句）
I had a snack， just in case there was no time to eat later. 我吃了些点心，因为怕过会儿没有时间吃饭。（将in case译成“因为怕”，将之视为原因状语从句）
Here's a contact number， in case there should be a problem. 这是联系电话，以防有问题出现。（将in case译成“以防”，将之视为目的状语从句）
Here's a contact number， in case there should be a problem. 这是联系电话，因为怕有问题出现。（将in case译成“因为怕”，将之视为原因状语从句）
七、用for fear (that) 表目的
for fear that 用于引导目的状语从句时，与 in case 大致同义，意思是“以防”“以免”。如：
He’s working hard for fear (that) he should fail. 他在努力工作唯恐他会失败。
She finally ran away for fear that he would kill her. 她最后逃走了，因为怕被他杀了。
Scientists reject a total ban for fear it will undermine efforts to stop the spread of malaria. 科学家们反对全面禁止，以免削弱为防止疟疾扩散所作的努力。
注：与in case一样，for fear that 引导的从句有时也被理解为原因状语从句，并将其翻译为“因为怕……”。比较：
Shut the window for fear that it may rain. 把窗子关上以防下雨。（将for fear that 译成“以防”，将之视为目的状语从句）
Shut the window for fear that it may rain. 把窗子关上，因为怕下雨。（将for fear that 译成“因为怕”，将之视为原因状语从句）