因为 / 所以 ...
Reach for this when you want to explicitly link a reason to its result — 'because X, so Y.' It's the workhorse cause-and-effect connector in Chinese. The textbook form uses both halves ('因为...所以...'), but in real spoken Chinese either half can stand alone: 因为下雨, 我没出去 or 下雨了, 所以我没出去 are both natural. Use the full pair when the logic needs to be unmistakable.
Structure
因为 [REASON]，所以 [RESULT] / 所以 [RESULT]
yīnwèi... suǒyǐ...
How to Think About It
Chinese keeps BOTH halves available. Where English picks 'because' OR 'so,' Chinese says either or both — and using both is the cleanest, most explicit. Dropping 因为 keeps the reason implicit ('下雨了，所以...' = 'It rained, so...'). Dropping 所以 keeps the conclusion hanging in a way that sometimes feels incomplete in writing. When in doubt, include both.
Examples
因为下雨，所以我没出门。
Yīnwèi xià yǔ, suǒyǐ wǒ méi chū mén.
Because it was raining, I didn't go out.
因为他工作太忙，所以没能完成这个梦想。
Yīnwèi tā gōngzuò tài máng, suǒyǐ méi néng wánchéng zhè gè mèngxiǎng.
Because his work was too busy, he wasn't able to fulfill that dream.
因为这双鞋很轻，所以现在所有的运动员都穿。
Yīnwèi zhè shuāng xié hěn qīng, suǒyǐ xiànzài suǒyǒu de yùndòngyuán dōu chuān.
Because these shoes are light, all the athletes now wear them.
Common Mistake
Learners put 因为 in the middle of a sentence like English 'I stayed home because it rained.' Chinese strongly prefers reason FIRST, result second: '因为下雨，所以我在家.' Mid-sentence 因为 ('我在家因为下雨') sounds translated and unnatural.
我没去公司因为下雨。
因为下雨，所以我没去公司。
Don't Confuse With
由于...因此...
Same meaning, formal register. Use 由于...因此 in essays, reports, and news; 因为...所以 in everyday speech.
之所以...是因为...
之所以...是因为... flips the order — result first, reason after. Use it when the result is the topic everyone's wondering about, and the reason is the punchline.
既然...就...
既然 = 'since' — argues from a fact both speakers already know. 因为 introduces fresh information as the cause. Pick by whether the reason is shared or new.
Practice
___ 下雨，所以我没出门。
Show answer
因为
因为他很累，___ 早早睡了。
Show answer
所以
Arrange: 所以 / 因为 / 他 / 没来 / 病了
Show answer
因为他病了，所以没来。
Because I was hungry, I went to eat.
Show answer
因为我饿了，所以去吃饭了。
Explain a recent decision using 因为...所以...
Show answer
因为今天天气很好，所以我决定去公园散步。
Hear It in Real Episodes
This pattern appears in 1 Fluentide episode: