Empiriomonism is Alexander Bogdanov's scientific-philosophical substantiation of Marxism. In Books One and Two, he combines Ernst Mach's and Richard Avenarius's neutral monist philosophy with the theory of psychophysical parallelism and systematically demonstrates that human psyches are thoroughly natural and are subject to nature's laws. In Book Three, Bogdanov argues that empiriomonism is superior to G. V. Plekhanov's outdated materialism and shows how the principles of empiriomonism solve the basic problem of historical materialism: how a society's material base causally determines its ways of thinking. Bogdanov concludes that empiriomonism is of the same order as materialist systems, and, since it is the ideology of the productive forces of society, it is a Marxist philosophy.