Therefore / hence (literary 故)

Structure Cause / reason，(是)故 + conclusion

故 (gù) is a Classical Chinese causal connector still used in formal, legal and essayistic prose to chain a conclusion: "therefore, hence, thus". 证据确凿，故予以采纳 = "the evidence is conclusive; therefore it is admitted". The variant 是故 ("for this reason") is even more solemn and belongs to texts with a classical tone. It is equivalent to 因此 / 所以 (HSK 4) but outdoes them in formality and concision: it appears with no subject before it and usually opens the closing clause. In speech it would sound affected.

Examples

证zhèng据jù确què凿záo，故gù予yǔ以yǐ采cǎi纳nà。
The evidence is conclusive; therefore it is admitted.
此cǐ事shì关guān系xì重zhòng大dà，故gù须xū谨jǐn慎shèn处chǔ理lǐ。
This matter is of great import; hence it must be handled with caution.
人rén无wú远yuǎn虑lǜ，必bì有yǒu近jìn忧yōu，是shì故gù当dāng未wèi雨yǔ绸chóu缪móu。
One who takes no thought for the distant will soon have troubles at hand; for this reason one should prepare in advance.
原yuán文wén已yǐ失shī，故gù无wú从cóng考kǎo证zhèng。
The original text has been lost; therefore there is no way to verify it.

Levels are indicative: they follow the standard Chinese Grammar Wiki (AllSet Learning) progression, not an official HSK 3.0 mapping. We never assign levels by eye.

This point and the other 370, with audio on every example, inside Wanyu.