These characters combine in a wonderfully clever way. They form the names of two fictional characters: 子虚 (Zǐ Xū), which translates to “Master Void,” and 乌有 (Wū Yǒu), which translates to “Mr. Nothingness” or “Mr. Non-existent.” So the idiom literally means “Master Void and Mr. Nothingness,” perfectly capturing the essence of something that is entirely made up.
The term 子虚乌有 originates from a masterpiece of literature called “The Rhapsody of Sir Void” (《子虚赋》, Zǐ Xū Fù), written by the Han Dynasty poet Sima Xiangru (司马相如). In the story, a fictional envoy named Zǐ Xū (Master Void) boasts to an official from another state about the glories of his own king's hunting grounds. In a follow-up piece, another fictional character named Wū Yǒu (Mr. Nothingness) refutes him. A third character, Wú Shì Gōng (无是公, Lord No Such Person), then steps in to describe the emperor's even grander park. Because the entire story, including its characters and the events described, was a literary creation, the names of the two main debaters were combined to form an idiom meaning “completely fabricated.” Using this term shows a degree of education and cultural literacy. In Western culture, we might say something is “a tall tale,” “pure fiction,” or “a figment of your imagination.” 子虚乌有 is similar but carries a more formal, literary weight due to its specific origin. It's less like saying “that's a fairy tale” and more like directly referencing characters from a classic text to make your point, which adds a layer of intellectual authority to the denial.
This idiom is versatile and appears in both formal and informal contexts.