Friedrich Albert Lange is usually regarded as a representative of physiological neo-Kantianism or as a forerunner of the Marburg school of neo-Kantianism. In this paper I try to reconstruct Lange’s theory of values to argue that his philosophy is better framed as an intermediate point in the development of the two-world theory (facts/values) between Hermann Lotze and Southwestern neo-Kantianism.

According to the received view, Charles S. Peirce's theory of diagrammatic reasoning is derived from Kant's philosophy of mathematics. For Kant, only mathematics is constructive/synthetic, logic being instead discursive/analytic, while for Peirce, the entire domain of necessary reasoning, comprising mathematics and deductive logic, is diagrammatic, i.e. constructive in the Kantian sense. This shift was stimulated, as Peirce himself acknowledged, by the doctrines contained in Friedrich Albert Lange's Logische Studien (1877). The present paper reconstructs Peirce's reading of Lange's book, and illustrates (...) what, according to Peirce, was right and what was problematic in Lange's account of reasoning. It further seeks to explain how Peirce's theory of deductive reasoning was a combination of Kant's philosophy of mathematics and Lange's philosophy of logic. (shrink)