Mandarin uses the paired connecting words 因为/因為 yīnwei ‘because/since’ … 所以 suǒyǐ ‘therefore’ … to express cause and effect or reason and result. 因为/因為 yīnwei and 所以 suǒyǐ occur at the beginning of their clauses or right before the predicate. They can occur in the same sentence.
因为他没有很多钱，所以他不随便买东西。
因為他沒有很多錢，所以他不隨便買東西。
Yīnwei tā méi yǒu hěn duō qián, suǒyǐ tā bù suíbiàn mǎi dōngxi.
Because he doesn’t have a lot of money, therefore he doesn’t casually buy things.
When the subjects of the 因为/因為 yīnwei clause and the 所以 suǒyǐ clause are identical, the subject is often omitted in the second (所以 suǒyǐ) clause. In that case, 因为/因為 yīnwei is usually placed after the subject of the first clause.
我最近因为忙，所以没给你打电话。
我最近因為忙，所以沒給你打電話。
Wǒ zuìjìn yīnwei máng, suǒyǐ méi gěi nǐ dǎ diànhuà.
Because I have been busy recently, I haven’t called you.
When the subjects of the two clauses are identical, the subject may also be omitted from the first clause. This sentence is acceptable with or without 所以 suǒyǐ.
因为有事，(所以)王先生请假了。
因為有事，(所以)王先生請假了。
Yīnwei yǒu shì, (suǒyǐ) Wáng xiānsheng qǐng jià le.
Because he had business to attend to, Mr. Wang asked for time off.
The position of the 所以 suǒyǐ clause is fixed. It must come second in the sentence, after a clause that introduces the cause.
| Say this | Not this |
| 因为他是中国人，所以他会说中国话。 | *所以他会说中国话，因为他是中国人 |
| 因為他是中國人，所以他會說中國話。 | 所以他會說中國話，因為他是中國人 |
| Yīnwei tā shì Zhōngguó rén, suǒyǐ tā | Suǒyǐ tā huì shuō Zhōngguó huà, |
| huì shuō Zhōngguó huà. | yīnwei tā shì Zhōngguó rén. |
Because he is Chinese, (therefore) he can speak Chinese.
However, the 因为/因為 yīnwei clause may occur either first or second in the sentence. As the sentences above illustrate, when 因为/因為 yīnwei occurs in the second clause, 所以 suǒyǐ cannot be included in the first clause.
他会说中国话，因为他是中国人。
他會說中國話，因為他是中國人。
Tā huì shuō Zhōngguó huà, yīnwei tā shì Zhōngguó rén.
He can speak Chinese because he is Chinese.
王先生请假了，因为他有事。
王先生請假了，因為他有事。
Wáng xiānsheng qǐng jià le, yīnwei tā yǒu shì.
Mr. Wang asked for time off because he had a matter (to attend to).
Although you can include 因为/因為 yīnwei and 所以 suǒyǐ in the same sentence, it is often possible to have only 因为/因為 yīnwei or only 所以 suǒyǐ in a cause and effect sentence.
所以 suǒyǐ and not 因为/因為 yīnwei
我最近很忙，所以没给你打电话。
我最近很忙，所以沒給你打電話。
Wǒ zuì jìn hěn máng, suǒyǐ méi gěi nǐ dǎ diànhuà.
I have been very busy recently, so I haven’t called you.
因为/因為 yīnwei and not 所以 suǒyǐ
他因为病了，没来上课。
他因為病了，沒來上課。
Tā yīnwei bìng le, méi lái shàng kè.
Because he was sick, he didn’t come to class.
The following expressions introduce a cause or reason for some situation.
因为 (noun phrase) 的关系, …
因為 (noun phrase) 的關係, …
yīnwei (noun phrase) de guānxi, …
because of/due to (noun phrase), …
因为他朋友的关系，汽车的价格减少了。
因為他朋友的關係，汽車的價格減少了。
Yīnwei tā péngyou de guānxi, qìchē de jiàgé jiǎnshǎo le.
Because of his friend, the price of the car was reduced.
(noun phrase) (之)所以 situation1, 是因为 situation2
(noun phrase) (之)所以 situation1, 是因為 situation2
(noun phrase) (zhī) suǒyǐ situation1, shì yīnwei situation2
(nouns phrase’s) reason for situation1 is situation2
有些人之所以对工作不认真，是因为缺乏责任感。
有些人之所以對工作不認真，是因為缺乏責任感。
Yǒu xiē rén zhī suǒyǐ duì gōngzuò bù rènzhēn, shì yīnwei quēfá zérèngǎn.
The reason why some people don’t work conscientiously is because they lack a sense of responsibility.
我之所以不去美國，是因為身體不好。
Wǒ zhī suǒyǐ bù qù Měiguó, shì yīnweishēntǐ bù hǎo.
The reason why I am not going to America is that my health isn’t good.
由于/由於 (situation)
yóu yú (situation)
owing to, due to, because of, as a result of (situation)
由于/由於 yóu yú may be placed before or after the subject.
由于我的粗心大意，这次考试的成绩不好。
由於我的粗心大意，這次考試的成績不好。
Yóuyú wǒ de cūxīn dàyì, zhè ì kǎoshì de chéngjī bù hǎo.
Because of my carelessness, my grade on this exam was not good.
他由于不了解情况，造成了一个大错误。
他由於不瞭解情況，造成了一個大錯誤。
Tā yóuyú bù liáojiě qíngkuàng, zàochéng le yī gè dà cuòwù.
Because he did not understand the situation, he made a big mistake.
The inclusion of 所以 suǒyǐ ‘therefore,’ or 因而 yīn’ér ‘therefore,’ etc., makes the relationship between cause and effect or reason and result clearer.
由于/由於 (situation1), 所以 (situation2)
yóu yú (situation1), suǒyǐ (situation2)
or
由于/由於 (situation1), 因而 (situation2)
yóu yú (situation1), yīn’ér (situation2)
due to/because of (situation1), therefore (situation2)
由于买不到票，所以我们上不了火车。
由於買不到票，所以我們上不了火車。
Yóuyú mǎibudào piào, suǒyǐ wǒmen shàngbuliǎo huǒchē.
Because we could not get tickets, we couldn’t get on the train.
由于各自坚持自己的意见，因而无法达成协议。
由於各自堅持自己的意見，因而無法達成協議。
Yóuyú gèzì jiānchí zìjǐ de yìjiàn, yīn’ér wú fǎ dáchéng xiéyì.
Owing to the fact that everyone held onto his own opinion, there was no way to reach an agreement.
The result may be stated first in the sentence. The reason is then introduced with 由于/由於 yóu yú. 由于/由於 yóu yú must be preceded by 是 shì:
(situation2) 是由于/由於 (situation1)
(situation2) shì yóu yú (situation1)
situation2 is because of situation1
碰到一点儿困难就退缩，这都是由于你缺乏信心。
碰到一點兒困難就退縮，這都是由於你缺乏信心。
Pèngdào yīdiǎr kùnnan jiù tuìsuō, zhè dōu shì yóuyú nǐ quēfá xìnxīn.
(If) you retreat when you meet a little difficulty, this is because of your lack of confidence.
为了/為了 wéi le can be used to identify some noun phrase as the reason for performing some action.
为了/為了 (noun phrase)
wéi le (noun phrase)
because of/for the sake of (noun phrase)
我这样做，完全是为了你。
我這樣做，完全是為了你。
Wǒ zhèyàng zuò, wánquán shì wéi le nǐ.
My doing this is completely for you. (I’m doing this all for you.)
In this pattern, 为了/為了 wéi le introduces a desired effect or result.
为了 situation 起见 … ,
為了 situation 起見 … ,
wéi le situation qǐjiàn, …
in order to, for the purpose of (obtaining the situation)
为了安全起见，绝对禁止司机酒后开车。
為了安全起見，絕對禁止司機酒後開車。
Wéi le ānquán qǐjiàn, juéduì jìnzhǐ sījī jiǔ hòu kāi chē.
For the sake of safety, drivers are absolutely forbidden to drink and drive.
To inquire about the cause or reason for something, use the following expressions:
为什么/為甚麼？ wèi shénme? ‘why?’
为什么/為甚麼 wèi shénme is the most common and neutral expression used to inquire about the cause or reason for something.
你昨天为什么没来上课？
你昨天為甚麼沒來上課？
Nǐ zuótiān wèi shénme méi lái shàng kè?
Why didn’t you come to class yesterday?
你为什么还在这儿？
你為甚麼還在這兒？
Nǐ wèi shénme hái zài zhèr?
Why are you still here?
怎么？/怎麼？ zěnme? ’why? how come?’
怎么/怎麼 zěnme is used to inquire about the reason for something, at the same time conveying surprise or disapproval. It may not require an answer.
他说今天来，怎么没来？
他說今天來，怎麼沒來？
Tā shuō jīntiān lái, zěnme méi lái?
He said he was coming today. Why hasn’t he come?
你不说，我怎么知道？
你不說，我怎麼知道？
Nǐ bù shuō, wǒ zěnme zhīdao?
If you don’t say (if you don’t tell me), how can I know?
什么理由？/甚麼理由？ shénme lǐyóu? ’what is the reason?’
什么理由/甚麼理由 shénme lǐyóu is used to inquire about the reason for something. When the speaker uses this expression, he or she expects an answer.
你有什么理由要跟我离婚？
你有甚麼理由要跟我離婚？
Nǐ yǒu shénme lǐyóu yào gēn wǒ lí hūn?
What is the reason why you want to divorce me?
什么理由你不给我们工钱？
甚麼理由你不給我們工錢？
Shénme lǐyóu nǐ bù gěi wǒmen gōngqian?
What is the reason why you haven’t given us our wages?
凭什么？/憑甚麼？ píng shénme? ’on what basis?’ ‘by what right?’
凭什么/憑甚麼 píng shénme is a colloquial expression, most often used in speaking.
你凭什么打人？
你憑甚麼打人？
Nǐ píng shénme dǎ ren?
What right do you have to hit people?
你凭什么逮捕我？
你憑甚麼逮捕我？
Nǐ píng shénme dàibǔ wǒ?
On what grounds are you arresting me?
何故 hégù? and 为何/為何 wéi hé? ‘for what reason?’ ‘why?’
何故 hégù and 为何/為何 wéi hé are used only in formal (usually written) language.
他何故杀人？
他何故殺人？
Tā hégù shā rén?
Why did he kill someone?
为何惊慌？
為何驚慌？
Wéi hé jīnghuāng?
Why are (you) so frightened?
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