  Although Helmholtz’ philosophical work was not particularly well-received by professional philosophers like  Hermann Cohen, co-founder of the Marburg School of neo-Kantians, it exerted a powerful influence on physicists (Cohen 1885, 202–204). In particular, Max Planck was an early supporter of the sign-theory. But Planck never interpreted the sign-theory causally, like Helmholtz had in his earliest writings. Rather, Planck recognized that “our perceptions provide, not a representation of the external world” but, rather, “measurements furnish the physicist with a sign which he must interpret” (Planck 1960, 53; Planck 1933, 84). Furthermore, Planck generalized the sign-theory, arguing that it is not objects, in and of themselves, which are known, but the structural relations in which they stand to one another. His fundamental idea was that what is known are not the natures of ‘things’ but complex structures of relations connecting ‘things’ to one another (Planck 1933, 84ff. and 1960, 53). Thus, the ‘objects of knowledge’ are not objects at all but, rather, what is known are the relata of the structural networks of relations in which they stand to other relata. And, as recent developments have increased the level of abstraction of scientific thought, it has become further removed from its anthropomorphic origins. So the unification of the scientific world-picture is achieved through increasing abstraction which, in turn, drives structural representation, thus reducing the anthropomorphic elements in the scientific image of the world (Planck 1949, 105).  The result of Planck’s effort is a theory of knowledge which is structuralist, generalized from Helmholtz’ sign-theory of perception, but which nonetheless preserves the themes of unification and objectivity derived from Kant.