According to perennial philosophy each world religion or spiritual tradition, independent of its cultural or historical context, is simply a different interpretation of a single universal truth. It affirms that a direct insight into the nature of reality is a universal possibility whether gained after practice of spiritual disciplines and study of scriptures or through a wholly unanticipated illuminating experience of union with God or the "Ultimate". Aldous Huxley, who wrote a book on the subject titled The Perennial Philosophy defined it as:
“”The metaphysic that recognizes a divine Reality substantial to the world of things and lives and minds; the psychology that finds in the soul something similar to, or even identical to, divine Reality; the ethic that places man's final end in the knowledge of the immanent and transcendent Ground of all being; the thing is immemorial and universal. Rudiments of the perennial philosophy may be found among the traditional lore of primitive peoples in every region of the world, and in its fully developed forms it has a place in every one of the higher religions." (The Perennial Philosophy, p. vii).