 When Lange died in 1875, he was working on a revision of the History of Materialism, and on the first part of a work called the Logische Studien (Logical Studies). Hermann Cohen saw the Logische Studien to press and wrote a short introduction. While the argument of the Logische Studien remains incomplete, it makes several contributions, some ahead of their time. Thiel (1994) and Patton (2011) are appreciations of the Logische Studien, Wille (2011) is a review of Patton (2011). Bellucci (2013) examines accounts of diagrammatic reasoning in Lange and in Charles Sanders Peirce.