Despite the flood of Mao's previously unknown works released by Red Guards during the Cultural Revolution, no pre-liberation versions of his “celebrated philosophical essays” On Contradiction and On Practice came to light from that source. This gap in the Red Guard material may have been viewed as significant, confirming suspicions held by some that there were in fact no pre-liberation versions of these essays, and showing more conclusively the mendacity of the Chinese claim that they were originally written in 1937. Arthur Cohen, perhaps the most vociferous critic of Mao's “originality” as philosopher, argued in 1964 that both essays had been written in the period 1950 to 1952, and that the Chinese claim “appears to be fraudulent.” Doolin and Golas also contest the Chinese claim that On Contradiction was written by Mao in 1937. In both cases, the motivation for this falsification of the date of composition is interpreted as being the desire to backdate Mao's status as a Marxist theoretician to the early Yan'an period. Schram and Wittfogel, however, have both accepted the possibility that On Contradiction and On Practice could have been written in 1937, while not denying that the 1950 and 1952 texts could represent heavily revised versions of earlier pieces. Schram, in fact, has argued that Mao's Lecture Notes on Dialectical Materialism, On Practice and On Contradiction belonged to “a single intellectual enterprise, namely Mao's attempt to come to terms with the philosophical basis of Marxism from the time he was first exposed to it in July 1936 until the Japanese attack of September 1937 turned his attention to more practical things.”