口是心非

Origin and story

Ge Hong's Baopuzi tells a Daoist tale about Cheng Wei, who wants to learn the art of making precious metals. His wife possesses knowledge he lacks but refuses to teach someone she considers unworthy. When he resorts to pressure and plots coercion, she insists that someone whose words and heart disagree cannot receive the teaching, even under threat.

This is a religious wonder tale, not evidence that alchemical transmutation worked. Its wording includes 口是而心非; the exact four-character form also appears in the book's Wei Zhi chapter among descriptions of misconduct. The modern idiom condemns the gap between what someone says and what they really think or intend.