身為臺灣現代派重要一員的郭松棻（1938－2005），曾投筆從戎獻身海外保釣，爾後又回歸文壇的傳奇生涯，已為研究者津津樂道。相對於此，郭松棻的早期作品，乃至他的思想與政論書寫，卻仍乏人問津。本文從郭松棻發表於1970年的〈秋雨〉出發，首先透過「宣言」的角度，鉤沉在這篇訣別殷海光（1919－1969）的文章深處糾葛著的自由主義與存在主義論辯，循此回溯郭松棻六○年代的譯介沙特（Jean-Paul Sartre, 1905－1980）與卡繆（Albert Camus, 1913－1960），另一方面闡連他七○年代的介入現實政治，以及伴隨這一介入而來的政論文章（以批判自由派為基調）和思想寫作（以重估存在主義為目標）。整體而言，本文奠定於作家作品、文學史與政治思想史三個層面，除了解析〈秋雨〉，亦以此闡述郭松棻的政治與思想轉折在臺灣人文語境中的獨特意義。

As one of the key figures in Taiwanese modernism, Kuo Song-fen's 郭松棻 (1938-2005) widely divergent trajectories, which are fraught with tensions between creative writing and political engagement, between ideologies of liberalism and existentialism, have yet to be placed under close scrutiny. In contrast to the increasing attention on his well-wrought fictions published in the 1980s, less scholarship has been dedicated to Kuo's various discursive practices before his literary turn, most of which are more relevant to his political dissidence and theoretical compositions. Focusing on “Autumn Rain,” a piece published in 1970, this paper sees the text as a manifesto that bids farewell to his mentor Yin Hai-kuang 殷海光 (1919-1969) on the one hand, and, on the other, as a threshold that transforms his early interpretation of Camus' (1913-1960) liberalism and Sartre's (1905-1980) existentialism into a discursive and activist engagement in the Baodiao 保釣 movement. Overall, this paper seeks to investigate Kuo Song-fen's “Autumn Rain” from different aspects such as literary history and the development of political thought, thereby illuminating the significance of his political and ideological conversions.