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...