More than twenty-five centuries have passed since that which has been called the Perennial Philosophy was first committed to writing; and in the course of those centuries it has found expression, now partial, now complete, now in this form, now in that, again and again. In Vedanta and Hebrew prophecy, in the Tao Teh King and the Platonic dialogues, in the Gospel according to St. John and Mahayana theology, in Plotinus and the Areopagite, among the Persian Sufis and the Christian mystics of the Middle Ages and the Renaissance - the Perennial Philosophy has spoken almost all the languages of Asia and Europe and has made use of the terminology and traditions of every one of the higher religions. But under all this confusion of tongues and myths, of local histories and particularist doctrines, there remains a Highest Common Factor, which is the Perennial Philosophy in what may be called its chemically pure state. This final purity can never, of course, be expressed by any verbal statement of the philosophy, however undogmatic that statement may be, however deliberately syncretistic. The very fact that it is set down at a certain time by a certain writer, using this or that language, automatically imposes a certain sociological and personal bias on the doctrines so formulated. It is only in the act of contemplation when words and even personality are transcended, that the pure state of the Perennial Philosophy can actually be known. The records left by those who have known it in this way make it abundantly clear that all of them, whether Hindu, Buddhist, Hebrew, Taoist, Christian, or Mohammedan, were attempting to describe the same essentially indescribable Fact.