The Mandarin 以 (yǐ) Family: 以为, 以及, 以便, 以免, 以来 and 以...为...

One old verb, six hats

以 (yǐ) started life as a full verb meaning 'take' or 'use'. Modern Mandarin does not use it that way any more, and you will almost never see it alone in speech. What it left behind is a family of frames, and once you can see the old verb inside each one, the family holds together:

Five of the six belong to written and formal Mandarin. 以为 (yǐ wéi) is the exception: it is thoroughly spoken, and it is the one you will use most.

以为 (yǐ wéi): the assumption that turned out wrong

This is the single most useful member of the family, and the one learners most often get subtly wrong. 以为 (yǐ wéi) does not mean 'think'. It means 'I took it to be so, and it wasn't'.

• 我以yǐ为wéi你今天不来。 (Wǒ yǐ wéi nǐ jīn tiān bù lái.) - I thought you weren't coming today. (You came.)
• 我以yǐ为wéi他是老师，原来他是学生。 (Wǒ yǐ wéi tā shì lǎo shī, yuán lái tā shì xué shēng.) - I thought he was the teacher; it turns out he's a student.
• 你以yǐ为wéi我不知道吗？ (Nǐ yǐ wéi wǒ bù zhī dào ma?) - You thought I didn't know?

The wrongness is built in. You do not have to say 'but I was wrong'; using 以为 (yǐ wéi) already says it. This is why 以为 (yǐ wéi) sounds strange for a belief you still hold.

Three near neighbours, kept apart:

• 以yǐ为wéi (yǐ wéi) - assumed, and was mistaken. 我以为今天不上课。 (Wǒ yǐ wéi jīn tiān bù shàng kè.) - I thought there was no class today. (There was.)
• 认rèn为wéi (rèn wéi) - consider, hold the view that. Neutral, and often formal. 我认为这个办法最好。 (Wǒ rèn wéi zhè ge bàn fǎ zuì hǎo.) - I take the view that this is the best method.
• 觉jué得de (jué de) - feel, reckon. Soft, personal, spoken. 我觉得今天有点冷。 (Wǒ jué de jīn tiān yǒu diǎn lěng.) - I feel it's a bit cold today.

If you say 我以为这个办法最好 (wǒ yǐ wéi zhè ge bàn fǎ zuì hǎo), a Chinese listener waits for the rest of the sentence, because you have just announced that you were wrong about it.

Where 以 (yǐ) hides: 可以, 所以, 以前, 以后

You already own four 以 words without having studied the character:

• 可以 (kě yǐ) - may, can. Literally 'permissible to use'.
• 所以 (suǒ yǐ) - therefore. Literally 'that by which', the means by which the result came.
• 以前 (yǐ qián) - before. 'Taking from that point, earlier.'
• 以后 (yǐ hòu) - after.

That gives you the one hard rule about bare 以 (yǐ): it is never a modal on its own. 我以去 (wǒ yǐ qù) is not a sentence. 'Can' is 可以 (kě yǐ), 能 (néng) or 会 (huì), and the 以 in 可以 is only ever the second half of the pair.

以及 (yǐ jí): 'and' for a written list

以及 (yǐ jí) joins nouns or noun phrases, like 和 (hé), but it belongs to writing. It typically attaches the last item, and often the least important one.

• 这本书介绍了中国的历史、文化以yǐ及jí艺术。 (Zhè běn shū jiè shào le Zhōng guó de lì shǐ, wén huà yǐ jí yì shù.) - This book covers Chinese history, culture and art. (艺术 (yì shù) = art.)
• 会上讨论了价格、时间以yǐ及jí地点。 (Huì shàng tǎo lùn le jià gé, shí jiān yǐ jí dì diǎn.) - The meeting discussed price, time and place.

Two limits worth pinning down:

1. 以及 (yǐ jí) does not join clauses. For that you want 而且 (ér qiě) or 并且 (bìng qiě). 我很累以及我很饿 (wǒ hěn lèi yǐ jí wǒ hěn è) is wrong; say 我很累，而且很饿 (wǒ hěn lèi, ér qiě hěn è).
2. It is not a spoken 和 (hé). Asking a friend 你喝茶以及咖啡吗 (nǐ hē chá yǐ jí kā fēi ma) sounds like a written form read out loud. Say 和 (hé).

以便 (yǐ biàn) and 以免 (yǐ miǎn): purpose, positive and negative

These are a matched pair, and they are the clearest single upgrade this article offers your written Mandarin. Both open the SECOND clause and state the purpose of the first.

以yǐ便biàn (yǐ biàn) = so that, in order to make it possible.

• 请提前告诉我们，以yǐ便biàn我们安排座位。 (Qǐng tí qián gào su wǒ men, yǐ biàn wǒ men ān pái zuò wèi.) - Please tell us in advance so that we can arrange seats. (提前 (tí qián) = in advance; 座位 (zuò wèi) = seat.)
• 请写清楚地址，以yǐ便biàn我们寄给你。 (Qǐng xiě qīng chu dì zhǐ, yǐ biàn wǒ men jì gěi nǐ.) - Please write the address clearly so we can post it to you.

以yǐ免miǎn (yǐ miǎn) = so as to avoid, lest.

• 请把日期写下来，以yǐ免miǎn忘记。 (Qǐng bǎ rì qī xiě xià lái, yǐ miǎn wàng jì.) - Write the date down so you don't forget.
• 路上小心，以yǐ免miǎn出事。 (Lù shàng xiǎo xīn, yǐ miǎn chū shì.) - Be careful on the way, so nothing goes wrong.
• 出门前请关好门窗，以yǐ免miǎn下雨。 (Chū mén qián qǐng guān hǎo mén chuāng, yǐ miǎn xià yǔ.) - Close the doors and windows before you go out, in case it rains.

The trap is negation. 免 (miǎn) already means 'avoid', so the bad outcome goes in positively after it. 以免不忘记 (yǐ miǎn bù wàng jì) says 'so as to avoid not forgetting', which is the opposite of what you meant. English 'so that you do NOT forget' has the negative; Mandarin 以免忘记 (yǐ miǎn wàng jì) does not.

以来 (yǐ lái): since, and still going

以来 (yǐ lái) follows a time expression and marks a stretch that starts there and runs up to the present. It sits AFTER the time, unlike English 'since'.

• 三年以yǐ来lái，这个城市变化很大。 (Sān nián yǐ lái, zhè ge chéng shì biàn huà hěn dà.) - Over the last three years, this city has changed a lot.
• 他来中国以yǐ来lái，中文进步很快。 (Tā lái Zhōng guó yǐ lái, Zhōng wén jìn bù hěn kuài.) - Since he came to China, his Chinese has improved fast.
• 自zì从cóng去年以yǐ来lái，我没见过他。 (Zì cóng qù nián yǐ lái, wǒ méi jiàn guo tā.) - I haven't seen him since last year. (自从 (zì cóng) = starting from; the two often pair up.)

Do not confuse it with 以后 (yǐ hòu):

• 三年以yǐ后hòu (sān nián yǐ hòu) - three years LATER. A point in the future.
• 三年以yǐ来lái (sān nián yǐ lái) - over the PAST three years. A stretch ending now.

Because 以来 (yǐ lái) reaches the present, the clause after it usually reports a change or an ongoing state, not a single finished event.

以...为... (yǐ ... wéi ...): take X as Y

This is the old verb showing itself most plainly: 以 (yǐ) takes something, 为 (wéi) says what it is treated as. The frame is fixed, and the two halves must both appear.

以yǐ + X + 为wèi + Y = take X as Y / treat X as Y / regard X as Y.

• 这个学校以yǐ学生为wèi中心。 (Zhè ge xué xiào yǐ xué shēng wéi zhōng xīn.) - This school puts the student at the centre.
• 我们以yǐ他为wèi例。 (Wǒ men yǐ tā wéi lì.) - We take him as an example. (例 (lì) = example.)
• 这个地区以yǐ农业为wèi主。 (Zhè ge dì qū yǐ nóng yè wéi zhǔ.) - This area is mainly agricultural. (农业 (nóng yè) = agriculture; 为主 (wéi zhǔ) = as the main thing.)
• 他以yǐ工作为wèi重。 (Tā yǐ gōng zuò wéi zhòng.) - He puts work first.

A handful of the Y slots are worth learning whole, because they recur constantly in writing: 为主 (wéi zhǔ, as the main thing), 为中心 (wéi zhōng xīn, as the centre), 为例 (wéi lì, as an example), 为准 (wéi zhǔn, as the standard).

Note that 为 (wéi) here is the level-tone reading meaning 'to be, to act as', not the 为 (wèi) of 为什么 (wèi shén me).

Common mistakes

1. Using 以yǐ为wéi (yǐ wéi) for a belief you still hold. 我以为这个办法最好 (wǒ yǐ wéi zhè ge bàn fǎ zuì hǎo) tells your listener you have since changed your mind. For a current opinion use 认为 (rèn wéi) or 觉得 (jué de).
2. Bare 以yǐ (yǐ) as a modal. 我以帮你 (wǒ yǐ bāng nǐ) is not Mandarin. Use 可以 (kě yǐ), 能 (néng) or 会 (huì).
3. 以yǐ及jí (yǐ jí) joining clauses. It joins nouns only. Two full clauses need 而且 (ér qiě) or 并且 (bìng qiě).
4. A negative after 以yǐ免miǎn (yǐ miǎn). 以免 (yǐ miǎn) already carries the 'avoid'. Say 以免忘记 (yǐ miǎn wàng jì), not 以免不忘记 (yǐ miǎn bù wàng jì).
5. Swapping 以yǐ便biàn (yǐ biàn) and 以yǐ免miǎn (yǐ miǎn). 以便 (yǐ biàn) points at the good outcome you want; 以免 (yǐ miǎn) points at the bad outcome you are dodging. Getting them the wrong way round reverses the sentence.
6. 以yǐ来lái (yǐ lái) in front of the time. It follows the time expression: 三年以来 (sān nián yǐ lái), never 以来三年 (yǐ lái sān nián).
7. Half a 以yǐ...为wèi... frame. 这个学校以学生 (zhè ge xué xiào yǐ xué shēng) is an unfinished sentence. The 为 (wéi) half is not optional.
8. Using the written members in speech. 以及 (yǐ jí), 以便 (yǐ biàn) and 以免 (yǐ miǎn) in a casual chat sound like you are reading from a notice. In conversation say 和 (hé), 这样 (zhè yàng) and 别 (bié) instead.

See also

• Conjunctions - where 以及 (yǐ jí) sits next to 和 (hé), 而且 (ér qiě) and the rest of the joining kit.
• Modals and intent - 可以 (kě yǐ) against 能 (néng) and 会 (huì), and why the 以 in it cannot be peeled off.
• The 之 (zhī) set phrases - the other classical survivor, and the same lesson about learning frozen frames whole.
• Word order - where the 以便 (yǐ biàn) and 以免 (yǐ miǎn) purpose clauses attach in the shape of the sentence.