The Sufis is the first authoritative, responsible book on Sufism, and as such it fills a colossal gap in Western documentation of Eastern subjects. Following a mystical teaching and a way of life that have had an enormous, though largely unrecognized, impact on both the East and the West for four thousand years, the Sufis believe not that theirs is a religion, but that it is religion. This belief includes conscious evolution, whereby through an effort of will man can originate new faculties - the faculties of mental telepathy and prophecy are examples - and Sufis therefore believe ultimately in the limitless perfectibility of man. To its followers, Sufism is the secret tradition behind all religious and philosophical systems. Robert Graves says in his Introduction, "The natural Sufi may be as common in the West as in the East, and may come dressed as a general, a merchant, a lawyer, a schoolmaster, a housewife, anything. To be 'in the world, but not of it,' free from ambition, greed, intellectual pride, blind obedience to custom, or awe of persons higher in rank; that is the Sufi ideal."