Variability and substantiality. Kurd Lasswitz, the Marburg school and the neo-Kantian historiography of science

A trained physicist, Kurd Lasswitz (1848-1910) is best known as a novelist, the father of modern German science fiction, and as a historian of science, the initiator of the modern historiography of atomism. In the late 19th century, Lasswitz engaged in an intense dialogue with the emerging Marburg school of neo-Kantianism, contributing to shaping most of its defining tenets. By the end of the decade, this research had grown into a two-volume Geschichte der Atomistik (1890), which remains the most successful example of neo-Kantian historiography of science. Lasswitz combined attention to historical detail with the search for the intellectual tools (Denkmittel) without which the 'fact of science' would be impossible. In particular, Lasswitz regarded Huygens' kinetic atomism as a historical model of a successful scientific theory, shaped by the interplay of two conceptual tools: (a) substantiality, the requirement for identity of the subject of motion through time, which found its scientific expression in the extensive atom; (b) variability, the intensive tendency to continue in an instant, which found its conceptual fixation in the notion of 'differential'. By raising the problem of individuality in physics, Lasswitz offers a unique perspective on the utilization of the history of science in 19th-century neo-Kantian thought.