The Introduction juxtaposed natural law thought with legal positivism as the two main responses to the question "why are humanly posited laws binding?" I have just described how Aristotle elaborated a theory of natural law, a theory, though, which took nature as "a second nature." Unwritten customs were so immediately felt that they were considered "natural." The early Greek tribes shared such an unwritten sense of law, although, as we have just observed, the natural unwritten laws and the humanly posited laws were considered one and the same I now wish to take up the notion of invisibility and examine how modern legal thought has identified several very different senses of invisibility.