Chapter 4 argues that the sensus communis forms the keystone of Kant’s critical system. Kant develops his idea of the sensus communis as a response to the quid juris of the judgment of taste – by what right may I claim that this is beautiful? As a judgment made out in the territory, without a law, a judgment of taste is always in question. Kant’s development of the sensus communis is shown to rely on two senses of its historical usage, epistemological and social. Both of these uses of the term are developed in response to skepticism. Kant’s own use of the term, which refers to a sense that we can communicate with all other human beings, discloses to us that all human beings share a way of having the world, and, too, that we share a world in common. It thus grounds the universal character of both cognition and moral life.