The theme of this journal issue deals with the opposition between what can be said to be the “inside” and the “outside” of a culture or a civilization, a question that can be approached in different ways. To begin with, one may ask whether certain anthropological constants can be discerned in all of humanity or, to take the opposite approach, whether civilizations possess certain cultural features that are unique to them. An approach focusing on certain anthropological constants gives us access to an “inside” shared by all of humanity, whereas the latter approach is part of how a civilization demarcates itself from its “outside.” How “inside” and “outside” relate to each other had best be investigated historically, since cultural and social differentiation grow historically out of the common soil of anthropological constants. This article focuses on Reinhart Koselleck's oeuvre to illustrate this claim. Why Koselleck? To begin with, one may find in his work an “inside” defined in terms of a philosophical anthropology and a culturally defined “outside,” both of which he contrasts in an original and thought-provoking way. As I will argue, the contrast runs parallel to the one between historical ontology and historical epistemology that can be discerned in Koselleck's writings. I will show how the dichotomy between ontology and epistemology reappears in his notion of the saddle time (Sattelzeit)—that is, the period in which Western modern historical writing was born. Prior to the saddle time, history was seen as the product of the anthropological constants of human nature, but afterward, these constants had to give way to the belief in a historical development requiring a historical epistemology to achieve historical truth. This is how the “inside” (ontology) and the “outside” (epistemology) are interwoven in Koselleck's notion of the Sattelzeit. In sum, ontology provides an interculturally shared “inside,” whereas epistemology divides it into as many “insides” as there are different civilizations.