Historical materialism remains one of the intellectual bases of Marxism. It proposes that technological advances in modes of production inevitably lead to changes in the social relations of production. This economic "base" of society supports, is reflected by and influences the ideological "superstructure" which encompasses culture, religion, politics, and all other aspects of humanity's social consciousness. It thus looks for the causes of developments and changes in human history in economic, technological and, more broadly, material factors as well as the clashes of material interests among tribes, social classes, and nations. Law, politics, the arts, literature, morality and religion are understood by Marx to make up the superstructure as reflections of the economic base of society. Many critics have argued that this is an oversimplification of the nature of society and claim that the influence of ideas, culture and other aspects of what Marx called the superstructure are just as important as the economic base to the course of society, if not more so. However, Marxism does not claim that the economic base of society is the only determining element in society as demonstrated by the following letter written by Friedrich Engels, Marx's long-time contributor: