it, was in interaction with other planets. (Frege, "Der Gedanke") A towering figure in late 19thand early 20th-century German philosophy, Hermann Lotze (1817–81) was a major influence in continental Europe as well as England and North America. Not only Rickert, Cohen, and Husserl, but also Bradley, Royce, and James were all importantly influenced by his writings.1 However, despite a sizeable scholarly literature, and at least one recent high-profile monograph,2 Lotze no longer commands the kind of attention that inspired Heidegger to describe his Logik as the "foundational book of modern logic."3 Lotze wrote about all major areas of philosophy (including metaphysics, aesthetics, religion, and history of philosophy), but the work for which he is now primarily known is Logik, first published in 1843 and then in a substantiallyrevised version in 1874 as the first part of 1 For more on Lotze's influence, see Beiser (2013), 128–31, Dahlstrom (1994), 35–37, and Gottfried Gabriel's introduction to Lotze (1989a). 2 Beiser (2013), a study of Lotze and another forgotten giant of 19th-century German philosophy, Adolf Trendelenburg. 3 Quoted by Beiser (2013), 130 n. 9. 6 Platonism in Lotze and Frege Between Psyschologism and Hypostasis Nicholas F. Stang Platonism in Lotze and Frege 139 his System der Philosophie. Lotze's work on logic was part of a larger reaction against psychologism, empiricism, and naturalism in late 19thcentury German philosophy. In Book III, Lotze makes a famous distinction between existence (Dasein) and validity (Gültigkeit). The former characterizes the mode of being of mental and physical objects and events, while the latter