現代漢語的強調語氣副詞「可」有豐富的功能，但其來源卻始終沒有談清楚。雖然過去對其來源已提出許多種不同主張，但各派主張均有難以周全之處，而且也未能留意到「可」重讀與輕讀之別。本文主張，重讀的「可」源自可行義情態動詞，而輕讀用法則源自反詰副詞，文中將提出相應歷史證據以為支持，並探討這兩線演變所涉及的語用因素。

Mandarin ke (可) is an emphatic modal adverb with multiple functions, but its origin has remained unclear. Although there have been different proposals regarding its etymology, they do not paint a complete picture, nor do they account for the differences in strong versus light intonation. This paper provides historical evidence to argue that the two forms of ke have different origins: The strong one originated from a modal verb and the light one from a rhetorical interrogative adverb.