Purpose: 为了, 以便, 免得

Purpose clauses explain why someone does something, not in terms of cause but in terms of goal. The difference is subtle but real: cause looks backward ("I stayed home because it rained"), while purpose looks forward ("I brought an umbrella in order to stay dry"). These three words all express purpose, but they point in slightly different directions.

为了: "in order to," "for the sake of"

为了 (wèile) is the most common and versatile purpose word. It introduces the goal that motivates an action and can appear at the start of the sentence or right before the verb.

为了 + [Goal], [Action]

• 为了学好汉语，她每天练习两个小时。(Wèile xué hǎo Hànyǔ, tā měitiān liànxí liǎng ge xiǎoshí.) -- In order to learn Chinese well, she practices two hours every day.
• 他努力工作，为了给家人更好的生活。(Tā nǔlì gōngzuò, wèile gěi jiārén gèng hǎo de shēnghuó.) -- He works hard in order to give his family a better life.
• 为了健康，我戒烟了。(Wèile jiànkāng, wǒ jiè yān le.) -- For the sake of my health, I quit smoking.

为了 can take a verb phrase as its goal ("in order to learn Chinese") or a bare noun ("for the sake of health"). Both are natural.

One thing worth knowing: 为了 can also be used to explain that something was done on someone's behalf, not just toward a personal goal.

• 他为了朋友做了很多。(Tā wèile péngyou zuò le hěn duō.) -- He did a lot for his friend's sake.

以便: "so that," "in order to make it easier to"

以便 (yǐbiàn) is more formal than 为了 and appears mainly in writing. It introduces a purpose that makes the first action more convenient or easier to achieve. The sense is "so that it will be easier to" or "so as to enable."

[Action], 以便 + [Facilitated Goal]

• 请提前通知我，以便我做好准备。(Qǐng tíqián tōngzhī wǒ, yǐbiàn wǒ zuò hǎo zhǔnbèi.) -- Please notify me in advance so that I can prepare.
• 我把笔记整理好了，以便以后复习。(Wǒ bǎ bǐjì zhěnglǐ hǎo le, yǐbiàn yǐhòu fùxí.) -- I organized my notes so that I can review them later.
• 文件已发送，以便您查阅。(Wéndàn yǐ fāsòng, yǐbiàn nín cháyuè.) -- The document has been sent for your reference.

以便 almost always sits in the second clause, after the action has been stated. You do X, and then 以便 explains what that X is meant to enable. It is a common fixture in emails, instructions, and official notices.

免得: "so as to avoid," "lest"

免得 (miǎnde) expresses a negative purpose. Instead of stating what you want to achieve, it states what you want to avoid. The action is taken specifically to prevent the unwanted outcome that follows 免得.

[Action], 免得 + [Unwanted Outcome to Avoid]

• 你早点出发，免得堵车。(Nǐ zǎo diǎn chūfā, miǎnde dǔchē.) -- Leave early so you don't get stuck in traffic.
• 把药放好，免得孩子拿到。(Bǎ yào fàng hǎo, miǎnde háizi ná dào.) -- Put the medicine away so the kids don't get hold of it.
• 我提前查了路线，免得迷路。(Wǒ tíqián chá le lùxiàn, miǎnde mílù.) -- I checked the route in advance so I wouldn't get lost.

免得 sits at the start of the second clause, just like 以便. The action comes first, and 免得 explains the bad outcome that the action is designed to prevent. It works in both spoken and written Chinese and is not especially formal.

A close synonym is 以免 (yǐmiǎn), which means the same thing but sits at a slightly higher register and appears more in writing:

• 请小心，以免受伤。(Qǐng xiǎoxīn, yǐmiǎn shòushāng.) -- Please be careful so as to avoid injury.

How they compare

Word	Meaning	Register	Position
为了	In order to, for the sake of	Everyday	Usually the first clause
以便	So as to enable, so that it's easier to	Formal / written	Second clause
免得	So as to avoid, lest	Everyday to neutral	Second clause

为了 is by far the most common of the three and the one to reach for in daily conversation. 免得 is natural in speech when you want to name a result you are trying to prevent. 以便 is worth recognizing in formal writing and useful to have in your own written Chinese as you move into higher levels.