(因)……，故……: therefore, hence (written)
【高113】复句 / complex sentences (因果)
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
故 is a one-syllable 所以 kept for writing: the cause clause (with or without 因) is followed by 故 + result. In English: "hence", "therefore", "so". 他已经适应了国外的生活，故不打算再回国.
The cause clause may drop 因, and the result clause stays short, with no other connective: you never put 所以 next to 故. The register is that of notices, regulations, rulings and commentary (本店正在装修，故暂停营业); in speech you say 所以.
It is not the 故 of 故事, 故乡 or 故意. The pair 因为……所以…… serves speech and ordinary writing; 因……故…… is its lean, formal version: one linking word per clause.
Examples
他已经适应了国外的生活，故不打算再回国。
Tā yǐjīng shìyìng le guówài de shēnghuó, gù bù dǎsuàn zài huí guó.He has already got used to life abroad, so he does not plan to come back.
因不是体面的事情，故不敢说出来。
Yīn bú shì tǐmiàn de shìqing, gù bù gǎn shuō chūlái.Because it was not something respectable, he did not dare to say it.
本店正在装修，故暂停营业三天，敬请谅解。
Běndiàn zhèngzài zhuāngxiū, gù zàntíng yíngyè sān tiān, jìngqǐng liàngjiě.The shop is being refitted, so it will be closed for three days. We ask for your understanding.
因暴雨影响，部分路段封闭，故请市民尽量避免出行。
Yīn bàoyǔ yǐngxiǎng, bùfen lùduàn fēngbì, gù qǐng shìmín jǐnliàng bìmiǎn chūxíng.Because of the heavy rain, some stretches of road are closed, so residents are asked to avoid going out as far as possible.
原告的请求有事实和法律依据，故本院予以支持。
Yuángào de qǐngqiú yǒu shìshí hé fǎlǜ yījù, gù běnyuàn yǔyǐ zhīchí.The plaintiff's claim rests on the facts and on the law, so this court upholds it.
Common mistakes
✗ 因为他病了，故所以不来。 → ✓ 他病了，故不来。 (never two result connectives).
✗ 我很累，故我想睡觉。 → ✓ 我很累，所以想睡觉。 (in speech, 故 sounds like a written notice).
✗ 故他病了，不来。 → ✓ 因他病了，故不来。 (故 opens the result, never the cause).