Experts: Sufism, the religious philosophy of Islam, is described in the oldest extant definition as the apprehension of divine realities, and Mohammedan mystics are fond of calling themselves Ahl al-Haqq, 'the followers of the Real.' In attempting to set forth their central doctrines from this point of view, I shall draw to some extent on materials which I have collected during the last twenty years for a general history of Islamic mysticism-a subject so vast and many-sided that several large volumes would be required to do it anything like justice. Here I can only sketch in broad outline certain principles, methods, and characteristic features of the inner life as it has been lived by Moslems of every class and condition from the eighth century of our era to the present day... The Sufi who sets out to seek God calls himself a 'traveler' (salik); he advances by slow 'stages' (maqamat) along a 'path' (tariqat) to the goal of union with Reality...