The term Classical Marxism denotes the collection of socio-eco-political theories expounded by Karl Marx and Friedrich Engels. "Marxism", as Ernest Mandel remarked, "is always open, always critical, always self-critical". As such, Classical Marxism distinguishes between "Marxism" as broadly perceived and "what Marx believed", thus in 1883 Marx wrote to the French labour leader Jules Guesde and to Paul Lafargue (Marx's son-in-law) – both of whom claimed to represent Marxist principles – accusing them of "revolutionary phrase-mongering" and of denying the value of reformist struggle. From Marx's letter derives the paraphrase: "If that is Marxism, then I am not a Marxist".   American Marxist scholar Hal Draper responded to this comment by saying: "There are few thinkers in modern history whose thought has been so badly misrepresented, by Marxists and anti-Marxists alike".  On the other hand, the book Communism: The Great Misunderstanding argues that the source of such misrepresentations lies in ignoring the philosophy of Marxism, which is dialectical materialism. In large, this was due to the fact that The German Ideology , in which Marx and Engels developed this philosophy, did not find a publisher for almost one hundred years.
Shortly after Mao's death in 1976, Deng Xiaoping initiated socialist market reforms in 1978, thereby beginning the radical change in Mao's ideology in the People's Republic of China (PRC).  Although Mao Zedong Thought nominally remains the state ideology, Deng's admonition to " seek truth from facts " means that state policies are judged on their practical consequences; the role of ideology in determining policy, in many areas, has thus been considerably reduced. Deng also separated Mao from Maoism, making it clear that Mao was fallible and hence the truth of Maoism comes from observing social consequences rather than by using Mao's quotations as holy writ , as was done in Mao's lifetime. [ citation needed ]
Marxism was unquestionably one of the strongest influences upon the work of Max Weber, much of which is devoted either to testing, in a particular context, some part of Marx’s theories, or to reassessing in a more general way his concepts and methods. In the first of these directions, Weber’s best-known study is that on the origins of modern capitalism (1904–1905), which is intended to show that a body of religious ideas (the Protestant ethic) played a vital part in the development of European capitalism, alongside the economic changes and the rise of a new class, through the inculcation of new attitudes toward wealth, science, and work. From this first revision of Marx’s economic interpretation of history, Weber went on to examine on a wider scale the social influence of religious ideas, to amend and supplement the Marxist theory of classes, to outline a radically different theory of political power, and to suggest an interpretation of modern European history as a movement, not toward socialism but, rather, toward greater bureaucratic regulation.