German philosopher and Socialist, important for his refutation of materialism and for establishing a lasting tradition of Neo-Kantianism at the University of Marburg.

Lange was the son of theologian Johann Peter Lange and was educated at Cologne, Bonn, and Duisburg. In 1861 he became involved in politics. Among his best known works are Die Leibesübungen (1863; “On Physical Exercise”); Die Arbeiterfrage (1865; “The Worker Question”); Die Grundlagen der mathematischen Psychologie (1865; “The Foundation of Mathematical Psychology”); Geschichte des Materialismus und Kritik seiner Bedeutung in der Gegenwart (1866; History of Materialism); J. St. Mill's Ansichten über die soziale Frage (1866; “John Stuart Mill's Theories About the Social Question”). Lange left Germany in 1866 and moved to Winterthur, near Zürich, to write for a democratic newspaper. He also wrote the Neue Beiträge zur Geschichte des Materialismus (1867; “A New Contribution on the History of Materialism”) and in 1870 became professor of philosophy at the University of Zürich, resigning his post in 1872 because of the pro-French sympathies of the Swiss in the Franco-German War. He then accepted the chair of philosophy at the University of Marburg and was largely responsible for a Kantian revival there. His Logische Studien (“Studies in Logic”) was published in 1877, after his death.