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: stick the reason after 因为, the result after 所以, and you have a clean two-clause sentence anyone from HSK 1 onward will understand. Use it for everyday explanations: why you're tired, why you're late, why you didn't bring an umbrella.
Structure
因为 [REASON] 所以 [RESULT]
yīnwèi... suǒyǐ...
How to Think About It
Chinese keeps BOTH halves. In English you pick one — 'I was tired, SO I left' or 'BECAUSE I was tired, I left.' Chinese says both: '因为我累了,所以我走了.' Native speakers feel a sentence with only 因为 (no 所以) as hanging in the air — the conclusion isn't sealed. The pair acts as a single grammatical unit, not two interchangeable words.
Examples
因为下雨, 所以我没去公园。
Yīnwèi xiàyǔ, suǒyǐ wǒ méi qù gōngyuán.
Because it rained, I didn't go to the park.
因为他很忙, 所以没来。
Yīnwèi tā hěn máng, suǒyǐ méi lái.
Because he was busy, he didn't come.
因为太冷了, 所以我穿了两件毛衣。
Yīnwèi tài lěng le, suǒyǐ wǒ chuān le liǎng jiàn máoyī.
Because it was too cold, I put on two sweaters.
Common Mistake
English speakers often drop 所以 because doubling 'because' and 'so' sounds redundant in their head. In casual spoken Chinese you can drop one, but in writing and at HSK 1-3 you keep both. Always use both when you're learning — natives will read your sentence as more complete.
因为我累了, 我去睡觉了。
因为我累了, 所以我去睡觉了。
Don't Confuse With
由于...因此...
Same meaning, much more formal. Use 由于...因此... in written essays, news articles, and reports — not in everyday speech.
之所以...是因为...
Flips the order — result first, reason second ('The reason X is because Y'). Used for emphasis when you want to highlight the cause: '我之所以学中文, 是因为我喜欢中国电影.'
既然...就...
Looks similar but means 'since/given that' — it presents the reason as something already established, then suggests a consequence. '既然下雨了, 就别去了.' (Since it's raining, just don't go.) Less neutral, more conclusive.
Practice
___ 我饿了, 所以我吃了一个苹果。
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因为
因为他生病了, ___ 没来上课。
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所以
Put in order: [所以 / 因为 / 我 / 我 / 喜欢 / 它 / 买了]
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因为我喜欢它, 所以我买了。
Translate to Chinese: 'Because she likes coffee, she bought a cup.'
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因为她喜欢咖啡, 所以她买了一杯。
Write one sentence about why you are learning Chinese, using 因为...所以...
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Example answer: 因为我想去中国旅游, 所以我在学中文。 (Because I want to travel to China, I'm learning Chinese.)