Because / Therefore — 因为 & 所以

Reading mode:

Overview

因为 (yīnwèi) and 所以 (suǒyǐ) form the primary cause-and-effect pair in Mandarin. 因为 introduces the reason/cause and answers the question "Why?" (为什么); 所以 introduces the result/conclusion. Unlike English, which uses only "because" or "so" in one sentence, Mandarin commonly uses both together. They can also be used separately — but with one critical asymmetry: 因为 can stand alone, while 所以 always requires a preceding reason.

因为 introduces the cause; 所以 introduces the result. Use them together or separately — but 所以 always needs a preceding reason, while 因为 can stand alone.

Pattern(s)

Pattern	Notes
`因为 [Cause], 所以 [Result]`	Full pair — most explicit; “Because X, therefore Y”
`因为 [Cause], [Result]`	所以 dropped; cause is stressed
`[Cause], 所以 [Result]`	因为 dropped; result is stressed

The pair is clause-level — both 因为 and 所以 precede full clauses, not single words.

Core Examples

Chinese	Pinyin	English
因为下雨了，所以我们没去公园。	Yīnwèi xià yǔ le, suǒyǐ wǒmen méi qù gōngyuán.	Because it rained, we didn’t go to the park.
因为努力学习，所以他考得很好。	Yīnwèi nǔlì xuéxí, suǒyǐ tā kǎo de hěn hǎo.	Because he studied hard, he did well on the test.
因为下雨，我们没去。	Yīnwèi xià yǔ, wǒmen méi qù.	Because it rained, we didn’t go.
他很忙，所以没来开会。	Tā hěn máng, suǒyǐ méi lái kāihuì.	He was busy, so he didn’t come to the meeting.
他病了，所以没来。	Tā bìng le, suǒyǐ méi lái.	He got sick, so he didn’t come.

因为 — Giving the Reason

To explain why something happens, use 因为. It introduces the reason or cause and answers the question "Why?" (为什么 — wèishénme). Place 因为 before the clause that gives the reason — this signals to the listener: "Here comes the explanation."

因为 introduces the reason or cause. It answers "Why?" — place it before the reason clause.

Chinese	Pinyin	English
因为下雨，我们没去。	Yīnwèi xià yǔ, wǒmen méi qù.	Because it rained, we didn’t go.
因为很累，他早睡了。	Yīnwèi hěn lèi, tā zǎo shuì le.	Because he was tired, he went to bed early.
因为便宜，我买了。	Yīnwèi piányi, wǒ mǎi le.	Because it was cheap, I bought it.

Shop scene: a boy points to a SALE sign showing 便宜, with 因为 labelled on the arrow 因为便宜，我买了。— Because it was cheap, I bought it.

💡 Position flexibility: 因为 can come at the beginning (emphasising the reason) or after the main clause (emphasising the result). Both are correct: 我没去，因为下雨了。 (I didn’t go, because it rained.)

The 因为…所以 Pair

Pair 因为 with 所以 (so / therefore) to form a complete cause-effect structure. While English typically uses only "because" OR "so" in a single sentence, Mandarin commonly uses both together. The 因为 clause sets up the cause, and the 所以 clause delivers the effect.

Pair 因为 with 所以 for a full cause → effect sentence. Both are used in the same sentence — unlike English, which chooses one or the other.

Pattern: 因为 + Reason, 所以 + Result

Chinese	Pinyin	English
因为下雨了，所以我们没去公园。	Yīnwèi xià yǔ le, suǒyǐ wǒmen méi qù gōngyuán.	Because it rained, we didn’t go to the park.
因为努力学习，所以他考得很好。	Yīnwèi nǔlì xuéxí, suǒyǐ tā kǎo de hěn hǎo.	Because he studied hard, he did well on the test.
因为天气冷，所以我不出门。	Yīnwèi tiānqì lěng, suǒyǐ wǒ bù chūmén.	Because the weather is cold, I’m not going out.
因为手机没电了，所以我打不了电话。	Yīnwèi shǒujī méi diàn le, suǒyǐ wǒ dǎ bù liǎo diànhuà.	Because my phone has no battery, I can’t make calls.
因为作业很多，所以他十一点才睡觉。	Yīnwèi zuòyè hěn duō, suǒyǐ tā shíyī diǎn cái shuìjiào.	Because there was a lot of homework, he didn’t sleep until 11.

Two sad children indoors, sharing a thought bubble of the sunny park they wished they could visit, rain falling outside 因为下雨了，所以我们没去公园。— Because it rained, we didn’t go to the park.

📝 Using 因为 alone is perfectly fine in casual conversation. The 因为…所以 pair is not required every time.

所以 Must Follow the Reason

所以 states a result, conclusion, or consequence. It always appears after the reason and signals that what follows is the logical outcome of what was just said. It cannot start a sentence unless the cause has already been clearly established in the previous sentence.

所以 introduces the result. It always follows a reason — it cannot start a sentence on its own.

Chinese	Pinyin	English
下雨了，所以比赛取消了。	Xià yǔ le, suǒyǐ bǐsài qǔxiāo le.	It rained, so the match was cancelled.
手机没电了，所以打不了电话。	Shǒujī méi diàn le, suǒyǐ dǎ bù liǎo diànhuà.	The phone has no battery, so I can’t make calls.
她哭了，所以眼睛红了。	Tā kū le, suǒyǐ yǎnjīng hóng le.	She cried, so her eyes are red.

Boy holding a dead phone with a low-battery icon; arrow and 所以 label point to a crossed-out phone call 手机没电了，所以打不了电话。— The phone has no battery, so I can’t make calls.

The reason must always come first:

	Chinese	Pinyin	English
✅ Correct	因为我工作很多，所以我很累。	Yīnwèi wǒ gōngzuò hěn duō, suǒyǐ wǒ hěn lèi.	Because I have a lot of work, I’m very tired.
❌ Incorrect	所以我很累，因为我工作很多。	Suǒyǐ wǒ hěn lèi, yīnwèi wǒ gōngzuò hěn duō.	(Incorrect order — the reason must come first)

	Chinese	Pinyin	English
✅ Correct	他病了，所以没来。	Tā bìng le, suǒyǐ méi lái.	He was sick, so he didn’t come.
❌ Incorrect	所以没来。(no prior context)	Suǒyǐ méi lái.	(Missing the reason — 所以 needs a preceding cause)

Exception in conversation: If the reason was just stated by another speaker, 所以 can stand alone. A: 我今天很累。 B: 所以早点睡吧。 (A: I’m very tired today. B: So go to bed early.) The cause was already established, so 所以 alone is natural.

Dialogue scene: one person says 我今天很累 and the other replies 所以早点睡吧 A: 我今天很累。B: 所以早点睡吧。— When the cause is already established in context, 所以 can stand alone in reply.

Drills

Fill in the blank with 因为 or 所以:

他昨天熬夜了，___ 今天很困。
___ 天气太热，我们决定去游泳。
妹妹哭了，___ 她的冰淇淋掉了。
___ 作业很多，他很晚才睡觉。
他很努力，___ 他进步很快。
___ 咖啡很苦，他加了糖。
她没来上课，___ 她生病了。
___ 明天有考试，我今天不出去玩。
他每天跑步，___ 身体很好。
___ 手机没电了，打不了电话。

Answer Key: 1. 所以 2. 因为 3. 因为 4. 因为 5. 所以 6. 因为 7. 因为 8. 因为 9. 所以 10. 因为

Notes

In speech, dropping one half of the pair is natural and common. Keeping both (因为…所以…) sounds slightly more formal or emphatic.
In written Chinese (essays, news), 因此 (yīncǐ) and 因而 (yīn’ér) are formal synonyms for 所以.
For the casual “then” consequence (你努力，就会成功), use 就 rather than 所以.

Sources

HSK Standard Course 2 — 因为 / 所以 (L6) Mandarin Grammar References — Conjunctions chapter