- 之所以 zhīsuǒyǐ reason whythe reason why (used after a noun or pronoun and before a predicate, typically followed by a clause explaining the cause)
- 所以然 suǒyǐrán rationalethe reason why
- 忘乎所以 wànghūsuǒyǐ carried awayto lose one's sense of propriety or self-control through excessive pride or excitement
- 不知所以 bùzhīsuǒyǐ at a lossto be confused and not know what to do or how to react
- 知其然而不知其所以然 zhīqírán'érbùzhīqísuǒyǐrán superficial understandingto know that it is so but not why it is so