Korsch was especially concerned that Marxist theory was losing its precision and validity – in the words of the day, becoming "vulgarized" – within the upper echelons of the various socialist organizations. His masterwork, "Marxism and Philosophy", is an attempt to re-establish the historic character of Marxism as the heir to Hegel. It commences with a quote from Vladimir Lenin's "On the Significance of Militant Materialism": "We must organize a systematic study of the Hegelian dialectic from a materialist standpoint." Korsch's critique of traditional bourgeois concept of progress in his work "Karl Marx" stressed that the development of material productive sources is not a natural result or a result of independent economic evolution and can be changed by man. He maintained that the revolutionary transformation of the mode of production and labor is essential to realize a proletarian revolution.