Abstract

Friedrich Albert Lange (1828-1875) author of a famous History of Materialism and Critique of Its Present Significance (1866, English transI. 1877-79, repr. 1925 with introduction by Bertrand Russell), was also interested in the epistemological foundations of formal logic. Part I of his intended two-volume Logische Studien was published posthumously in 1877 by Hermann Cohen, head of the Marburg school of neo-Kantianism. Lange, departing from Kant, claims that spatial intuition is the source of the apodeictic character not only of the truths of mathematics, but also of the truths of logic. He aims at showing this by basing validity and invalidity of syllogistic inferences on an interpretation of the standard forms (of proposition in assertoric syllogistic) with the help of the five kinds of possible relations (in fact what is known today as the Gergonne-Euler relations) between extensions of concepts given to us as areas in a plane, i.e.in space. Generality is achieved by considering all possible variations within each type of spatial relation, exhibiting a connection between concept and intuition reminding Lange of the Kantian "schema". Lange is well aware of the contemporary English "algebraic" logic, but he considers its approach as the appropriate one for a logic of content (Inhaltslogik) and not for a logic of extension (Umfangslogik). Lange did not live to enjoy the recognition by some leading logicians (amongst them John Venn, to whose reference in 1881 to Lange's "admirable Logische Studien" the present paper owes it title), nor could he respond to the many critics of his proposed foundation of logic. Its radicality as well as its broad reception (and discussion up to at least 1959) seem to entitle Lange's Logische Studien to an, if modest, place in the history of logic in the 19th century.