The other important contributions to Marx's revision of Hegelianism came from Engels's book, "The Condition of the Working Class in England in 1844", which led Marx to conceive of the historical dialectic in terms of class conflict and to see the modern working class as the most progressive force for revolution, as well as from the social democrat Friedrich Wilhelm Schulz, who in "Die Bewegung der Produktion" described the movement of society as "flowing from the contradiction between the forces of production and the mode of production."