"Truth is one, the sages speak of it by many names," he often quoted from the Vedas. Joseph Campbell was fascinated by what he viewed as universal sentiments and truths, disseminated through cultures which all featured different manifestations. He wanted to show his idea that Eastern and Western religions are the same on a very basic level, and that nobody is right but everyone is searching for the same unknown, and indeed unknowable, answer. He began to look paradoxically at moral systems as both incorrect and necessary. Like the postmodern relativists he believed such things as 'right' and 'wrong' are just contrived ideas, but also like them he understood a moral system is necessary from the perspective of a student of mythology and psychology. In this way he melded also the concepts of modernism and postmodernism, although some interpretations place him as a postmodernist before his time.

He believed all spirituality is searching for the same unknown transcendent force from which everything came and into which everything will return. He referred to this transcendent force as the connotation of what he called "metaphors", the metaphors being the various deities and objects of spirituality in the world.