Because/So (因为...所以)
因为...所以
因为...所以 (yīnwèi...suǒyǐ) connects a cause and its result, meaning "because...therefore." In spoken Chinese, you can use either half alone.
Pattern
因为 + Reason, 所以 + Result
Explanation
因为...所以 is a paired conjunction that expresses cause and effect. 因为 (yīnwèi) introduces the reason ("because"), and 所以 (suǒyǐ) introduces the result ("so/therefore"). The pattern is: 因为 + Reason, 所以 + Result.
For example, "因为下雨了，所以我没去公园" means "Because it rained, I didn't go to the park." This structure is very common in both spoken and written Chinese.
In everyday speech, you often hear just one half of the pair. You might say "因为下雨了，我没去公园" (dropping 所以) or "我没去公园，因为下雨了" (putting the reason at the end, English-style). You can also use 所以 alone: "下雨了，所以我没去公园." All of these are grammatically acceptable.
However, one critical rule to remember: in Chinese you CANNOT use both 因为 and 所以 AND also include 但是 or 可是 in the same sentence the way English speakers sometimes blend "because" with "but." Each paired conjunction operates independently.
Examples
因为下雨了，所以我们不去了。
Yīnwèi xià yǔ le, suǒyǐ wǒmen bú qù le.
Because it's raining, we're not going.
因为他生病了，所以没来上课。
Yīnwèi tā shēngbìng le, suǒyǐ méi lái shàng kè.
Because he was sick, he didn't come to class.
因为太贵了，所以我没买。
Yīnwèi tài guì le, suǒyǐ wǒ méi mǎi.
Because it was too expensive, I didn't buy it.
他很累，所以早睡了。
Tā hěn lèi, suǒyǐ zǎo shuì le.
He was tired, so he went to bed early.
所以 can be used alone without 因为
因为我喜欢中文，所以每天都学习。
Yīnwèi wǒ xǐhuān Zhōngwén, suǒyǐ měi tiān dōu xuéxí.
Because I like Chinese, I study every day.
Common Mistakes
Wrong
因为他很忙，但是他没来。
Correct
因为他很忙，所以他没来。
因为 pairs with 所以, not 但是. Don't mix cause-effect and contrast conjunctions.
Wrong
所以我没去，因为下雨了。
Correct
因为下雨了，所以我没去。
所以 (the result) should come after 因为 (the cause), not before it.
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