矛盾

A weapons merchant in the state of Chu was selling spears and shields. He called out to the crowd: "My shields are so strong, nothing can pierce them!" Then he called out: "My spears are so sharp, they can pierce anything!" A bystander asked: "What happens if you thrust your spear at your shield?" The merchant had no answer.

This story appears in the 韩非子 (Hánfēizǐ), the Legalist masterwork of the third century BCE. The merchant's paralysis in the face of the question is the original meaning: a logical impossibility, a self-defeating claim, a position that destroys itself by being pressed to its conclusion.

The two characters tell the story in their visual forms: 矛 (máo) is a spear — a character that shows a lance with its blade; 盾 (dùn) is a shield — a character depicting a rounded defensive object. Together they name the logical situation where one claim negates another.

The word has become so thoroughly absorbed into everyday Chinese that most speakers use it without thinking of the spear-and-shield parable. But the story is the reason the word exists, and knowing it makes the word feel earned rather than arbitrary.