 It is hard to interpret the Marburg rejection of the given. It seems to deny the obvious fact that there is some passive element in perception, and to leave no room for experiment within natural science (as Natorp recognized: 1912a: 186). In interpreting the doctrine, it is helpful to remember that the Marburg theory of knowledge concerns relations among the content of knowledge—how one part of the content of knowledge justifies another. It is not concerned with causal relations between acts of the mind in perception. Plausibly, the only content that could justify a thought must itself be something thinkable, since “knowledge is only grounded through other knowledge” (Natorp 1887: 168). (In this sense, the denial of the given is a denial of content that is not conceptual or dependent on what is conceptual.) In Cassirer’s polemic against the given, he attacks the “epistemological atomism” implicit in it: the view that there are some contents that can be efficacious for knowledge without requiring that a knower possess any concepts or know any facts. (In this sense, the denial of the given is a defense of semantic holism.) For this reason, he argues against the given by arguing that even the most basic experiments—measurements—depend on the experimenter possessing concepts and knowing certain theoretical facts (see  section 2.3  below).