本文旨在探討「可」三種疑問用法的來源與演變過程，分別是反詰、推度詢問與究問這三種。關於前兩種用法，過去文獻已指出反詰用法來自情態 動詞，而推度詢問用法則來自反詰用法，但所提證據多為旁證，本文將補上 直接證據。至於「可」的究問用法，過去一直未受重視，本文認為此用法衍 生自推度詢問用法，是故「可」的三種疑問用法有如下演變關係：「反詰>推度詢問>究問」。文中將藉語法化觀點推敲各演變環節所涉及的機制，並侧 重「可」語用功能的作用。據本文觀察，這三項演變都是受到特定語用需求 而展開的，「可」均因吸納語境義而形成新功能。

This paper investigates the origin and the formation of three interrogative usages of ke 可: rhetorical, conjectural, and persistent. Past researches have argued that the rhetorical interrogative usage of ke originated from the modal verb, while the conjectural interrogative usage in turn developed from the rhetorical usage. Most of the evidence given for this is circumstantial; this paper supplements this with direct evidence. In the past, limited attention has been given to the persistent interrogative usage of ke. This paper argues that this usage derives from the conjectural usage. To summarize, the three usages evolved in the following manner: rhetorical interrogative usage > conjectural interrogative usage > persistent interrogative usage. The present study also examines the mechanisms of each change from the perspective of grammaticalization theory, with particular emphasis on the pragmatic functions. We observe that the three developments were triggered by specific pragmatic demands, and that the new functions of ke were formed by the absorption of the contextual meaning.