本文考察「便」從上古至近代漢語的語法化演變，從動詞用法展開，逐一追蹤十二種語法功能的形成，並建構其語法化路徑。在其演變中，承接副詞與強調副詞是最為關鍵的功能，因「便」從這兩種功能各發展出多種副詞與連詞用法。無獨有偶，在歷史上經常與「便」相提並論的「即」與「就」不但也表現出多重語法化現象，甚至發展出的功能也無二致，這說明本文觀察的語法化演變在漢語史上有一定的普遍性。文中繼而探討承接副詞與強調副詞的特性，揭示三詞多重語法化之因，並確認其中演變環節並未違背語法化理論中的單向性假設。

This article examines the grammaticalization of Bian 便from ancient Chinese to early Mandarin Chinese by tracing its evolvement of using as a verb into twelve syntactic functions and accordingly constructs its path of grammaticalization. In the path the consecutive and emphatic adverbs are two key grammatical functions since most adverbial and conjunctional functions of Bian are derived from them. In addition to Bian, Ji 即and Jiu 就 underwent the same path of grammaticalization and also have developed the twelve functions as Bian has. This similarity indicates that the path of grammaticalization we propose in this article is representative in the history of Chinese language. My article also discusses the syntactic and semantic properties of consecutive and emphatic adverbs in order to explore the cause of Bian’s polygrammaticalization and thus confirms that the development of the three words does not contradict the hypothesis of unidirectionality.