The borrowing of the character “Mou” (某) originally meaning “sour plum” as a pronoun should lag far behind the spoken language. Therefore, the pronoun “Mou” (某) in the Chinese literature can no longer explain its origin. Through cognate affiliation and related analogy, it is inferred that the pronoun “Mou” (某) should go through such a stage of development as “negative indefinite pronoun to indefinite pronoun, and then to specific pronoun”. From the etymological point of view, the earliest usage of “Mou” (某) should be a negative indefinite pronoun. Zhou Guangye of the Qing Dynasty thought that the use of “Mou” (某) as a pronoun began with taboo, which was not the source of its pronoun usage. The usage of the word “Mou” (某) used as a taboo should be the third stage of its development.