魏晋时期,出身于名门的王衍从小伶牙俐齿,极有口才,但没有真才实学,华而不实。成年后的王衍更以谈论老庄哲学见长,常在公开场合讲授玄理。他讲授时总是穿着宽袍大袖的衣服,手里挥着玉柄麈尾,满嘴讲些玄妙荒诞的怪话。每逢义理讲得不恰当时,他就不假思索,随口更改。《晋书·王衍传》说他“义理有所不安,随即改更,世号口中雌黄”。“口中雌黄”日后衍化为“信口雌黄”, During the period of the Wei and Jin Dynasties, Wang Yan, who was born in the famous gate, had been eloquent and eloquent. However, he had no real knowledge and was spurious. After his adulthood, Wang Yan was better known for talking about Lao Zhuang’s philosophy and he often taught the mysticism in public. When he was teaching, he always wore big-sleeved suits, waving jade handles and tails, and spoke some mythical absurd monsters. Whenever justice is not appropriate, he will not hesitate to change his mind. “Jin Shu Wang Yan Chuan” said that he “was disturbed by righteous thoughts, then changed even more, the world number in the yellow mouth.” “Essay in the mouth” has evolved into a “female” in the future.