 There are, of course, many other philosophers whom one might want to include in the list of neutral monists. In the German speaking world we find Richard Avenarius (1843–96), who was in contact with Mach, and Joseph Petzoldt (1862–1929), who built on the work of Avenarius. Avenarius’s main reflections on neutral monism are contained in Avenarius 1888/90, 1891, and 1894/95. Petzoldt’s relevant works are Petzoldt 1900, 1904 and 1906. In the English speaking world, neutral monism thrived within the movement of American new realism. Ralph Barton Perry (1876–1957)—a student and friend of James—is the most visible neutral monist of this group. His 1912 is the main source for his views about neutral monism. And Edwin B. Holt (1873–1946) developed an ambitious neutral monist program in his 1912 and 1914.