"Friedrich Albert Lange (1828 - 1875) was a German philosopher, pedagogist, political activist, and journalist. Lange is a significant figure among the mid nineteenth century German intellectuals who were concerned to think through the impact of developments in natural science for politics, philosophy, and pedagogy.

Lange played a significant role in the German labour movement and in the development of social democratic thought. He articulated a socialist Darwinism that was an alternative to early social Darwinism. His work The History of Materialism and Critique of its Contemporary Significance was a classic text in materialism and the history of philosophy well into the twentieth century. The “materialism controversy” centered on the impact of materialist science and philosophy on religion and metaphysics. Lange’s response to the materialism controversy had an influence on the neo-Kantian movement and on Friedrich Nietzsche, among others. Lange was one of the originators of “physiological neo-Kantianism” and an important figure in the founding of the Marburg school of neo-Kantianism. His work in logic, culminating in Logical Studies, derived the syllogistic from diagrammatic reasoning, and was admired by Ernst Schröder and John Venn.

Lange’s sympathetic critique of materialism, his philosophical naturalism, and his political activism unite his diverse achievements, and distinguish him among nineteenth century philosophers." (SEP).

Harald Høffding (1843-1931) was one of the leading Danish philosophers of the turn of the century. His philosophy is greatly inspired by positivism, which around 1900, mainly due to Avenarius and Mach, came to be synonymous with empiriocriticism.