Two-level complex sentences (二重复句)
【六54】多重复句 / complex sentences
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
A 二重复句 is a complex sentence in which one of the blocks is itself a complex sentence: it has two levels. The outer level links two blocks with a connector (所以、但是、因此、同时…); the inner level links the clauses inside each block (虽然……但是……, 只要……就……, 如果……就……).
To read one, find the main break first: the widest connector or the strongest pause. In 虽然装电梯很贵，但是能用很多年，所以，只要费用合理，大家就会同意, the break is in front of 所以: the left block [虽然……但是……] is the premise, the right block [只要……就……] the conclusion. Then read each block with its own pair of connectors. An outer-level 所以 draws its conclusion from the whole preceding block, not just from the clause right before it.
In writing the main break is marked by a semicolon (；) and commas serve the inner level; in speech it is a longer pause. Pairs stay matched: 虽然 calls for 但是, 因为 for 所以, 如果 for 就.
You find them in the press, in speeches, in exam texts, and in any reasoning that stretches out, including in speech when someone argues a case.
Examples
他想去旅行，但是没有时间，所以只好把计划推迟了。
Tā xiǎng qù lǚxíng, dànshì méiyǒu shíjiān, suǒyǐ zhǐhǎo bǎ jìhuà tuīchí le.He wanted to travel but had no time, so he had to put the plan off.
虽然这家餐厅离得很远，但是菜很好吃，所以每到周末，总有很多人排队。
Suīrán zhè jiā cāntīng lí de hěn yuǎn, dànshì cài hěn hǎochī, suǒyǐ měi dào zhōumò, zǒng yǒu hěn duō rén páiduì.The restaurant is far away, but the food is excellent, so every weekend there is always a queue.
如果明天下雨，我们就不去爬山了；但是，如果只是阴天，我们还是去。
Rúguǒ míngtiān xià yǔ, wǒmen jiù bú qù pá shān le; dànshì, rúguǒ zhǐshì yīntiān, wǒmen háishi qù.If it rains tomorrow we won't go hiking; but if it is only overcast, we'll still go.
只要坚持锻炼，身体就会越来越好；但是，如果三天打鱼两天晒网，再好的计划也没有用。
Zhǐyào jiānchí duànliàn, shēntǐ jiù huì yuè lái yuè hǎo; dànshì, rúguǒ sān tiān dǎ yú liǎng tiān shài wǎng, zài hǎo de jìhuà yě méiyǒu yòng.If you keep exercising, your health will get better and better; but if you do it by fits and starts (fish for three days, dry the nets for two), even the best plan is useless.
这个方案虽然成本较低，但是风险很大；因此，公司决定先在一个城市试一试，再决定要不要推广。
Zhège fāngàn suīrán chéngběn jiào dī, dànshì fēngxiǎn hěn dà; yīncǐ, gōngsī juédìng xiān zài yí ge chéngshì shì yi shì, zài juédìng yào bu yào tuīguǎng.This plan is cheap but very risky; the company has therefore decided to try it in one city first and then decide whether to roll it out.
Common mistakes
✗ 虽然他很忙，所以他还是来了 → ✓ 虽然他很忙，但是他还是来了 (connector pairs do not cross: 虽然 calls for 但是, not 所以).
✗ reading the 所以 of "虽然……，但是……，所以……" as linked only to the clause right before it → 所以 draws its conclusion from the whole first block [虽然……，但是……].