在1919年五四運動和1989年六四運動之間，還有一個被遺忘的1976年四五運動。這三次非官方大規模群眾運動，不僅標誌二十世紀中國的三個關鍵歷史時刻，同時也象徵北京天安門廣場的三個生命史轉折點。「五四」、「四五」與「六四」三組數字，乃解讀二十世紀中國歷史、政治文化與天安門廣場生命史的符碼或「關鍵詞」（keywords）。本文從天安門廣場記憶政治與空間之社會生產的分析視角，探究四五運動的歷史意義，以及「四五」作為一個論述性「關鍵詞」意義之建構與變遷的脈絡。當學者集中檢視「五四」與「六四」之認同與記憶政治關係，本文在「天安門詩抄」等抗爭文學、中共官方歷史文本與報刊之詮釋基礎上，探析四五運動及其後政治變局中，群眾與中共如何不斷召喚或利用「五四」與「四五」符碼或「關鍵詞」。尤其，作為「四五」的文化記憶媒介，「天安門詩抄」讓我們得以剖析中共建政以來所建構的紀念性、儀式性與紀律性空間，如何被轉化成群眾挪用官定革命傳統，以合理化其悼念周恩來與批判「四人幫」的物質與文化基礎。亦即，天安門廣場此一官方紀律空間，在「四五」期間被建構為一個批判當權者的公共領域，再再呈現廣場意義的可變性與建構性。「天安門詩抄」提供一個「當下」視角觀察中共建政以來天安門廣場首次大規模非官方群眾運動之源起與發展，更可藉以細究「四五」記憶政治。它們呈現群眾如何賦與周恩來、「四五」與天安門廣場之另類新義；解釋何以群眾會在人民英雄紀念碑此一特定地點悼念周恩來；展示群眾如何利用人民紀念碑細數周恩來革命生涯的同時，挪用官定革命傳統或論述性關鍵詞「五四」來合法化對中國現代性的未來想像。再者，本文最後進一步爬梳中共官方「四五」論述及其意義之變遷，具體分析中共在「四五」之後如何透過「四五」之紀念，合法化鄧小平的重返權力核心及其「四個現代化」與「四項基本原則」論述，但卻突然在1980年中以後不再紀念「四五」，使之逐漸成為一個被官方遺忘的革命傳統。中共對「四五」的政治使用，不但說明歷史記憶的建構性，也展示官方歷史論述形構的權力因素，以及主宰性歷史論述在權力競逐上的作用。此一歷程，讓我們得以窺見「四五」作為檢視中華人民共和國歷史之「關鍵詞」的歷史化，亦即其民間與官方論述建構之源起與變遷，以及其與象徵過去歷史之「五四」關鍵詞間的關係，並作為未來進一步探究「四五」、「五四」與「六四」關鍵詞之間關聯性的基礎。

Between the May Fourth Movement of 1919 and the June Fourth Movement of 1989, there was the forgotten April Fifth Movement of 1976. The three large-scale unofficial protests not only constitute three defining moments in the Chinese pursuit of political modernity in the twentieth century, but also represent three turning points in the on-going changing meaning of Tiananmen (Gate of Heavenly) Square, the symbolic center of the People's Republic of China (PRC), which materialized the Chinese cultural memory of the communist-sanctioned revolutionary traditions. The magic numbers of ＂May Fourth,＂ ＂April Fifth,＂ and ＂June Fourth＂ not only signify three prominent watersheds in the history of twentieth-century China but also constitute three decoding codes, or ＂keywords,＂ to examine the changing meaning of Tiananmen Square and political culture of the PRC. This article is the first comprehensive inquiry into the significance of the April Fifth Movement from the perspectives of the politics of memory making and social production of space at Tiananmen Square. Through a close reading of the protest literature, such as the Tiananmen Poems and big- and small-character posters, as well as the historical documents of Chinese Communist Party (CCP) and newspapers, this article intends to analyze both the popular and official uses of ＂May Fourth＂ and/or ＂April Fifth＂ during and after the April Fifth Movement. Especially, the Tiananmen Poems allow us to see how the commemorative monuments and official ritual practices at Tiananmen Square have become the material and spatial foundation to recall and appropriate the past of the communist-sanctioned revolutionary tradition. It is in this way that the dissident protesters during the April Fifth Movement were able to justify their struggle against the Gang of Four in a short-lived public sphere that was created at the state disciplinary space of the PRC. This in turn illuminates the fluidity and constructed nature of the symbolism of Tiananmen Square. In addition to offering a present perspective to observe the genesis and development of the first unofficial social movement since the founding of the PRC, the Tiananmen Poems open a window to look into the dynamics of memory making in which the people from below have conceptualized and endowed alternative meanings with Zhou Enlai, ＂April Fifth,＂ and Tiananmen Square in their popular discourse. They explain why the popular mourners came to the particular site of the Monument to the People's Heroes at the center of Tiananmen Square to commemorate Zhou Enlai. Moreover, the Tiananmen Poems also demonstrate how the dissident protesters during and after the April Fifth Movement legitimatized their prospective envision of Chinese modernity, the Four Modernizations, by appropriating the past of the communist-sanctioned revolutionary tradition such as ＂May Fourth＂ while attaching their recollection of Zhou Enlai's career to the Monument. Furthermore, this article examines how the CCP had redefined and used ＂April Fifth＂ as a revolutionary tradition in order to endow Deng Xiaoping's rise to power and his discourses on the Four Modernizations and the Four Cardinals with social and historical legitimacy in the post-Mao China. This eventually shows how CCP and PRC kept silent about ＂April Fifth＂ and turned it into a forgotten revolutionary tradition after the mid-1980s. The official political use of ＂April Fifth＂ exemplifies constructed nature of historical memory as well as the power at work in the making of official discourse on the past and the power of discourse making at the present. This process witnessed the changing meaning of ＂April Fifth＂ in the popular and official discourse as a keyword to examine the history of the PRC and its relevance with other keywords such as ＂May Fourth＂ and ＂June Fourth.＂