According to the Sufi conception, there are several degrees distinguished as different stages of responsiveness; in other words, of higher initiation. Among them there are five principal ones: Wali, Ghous, Qutub, Nabi, Rasul, the sign of Rasul being the crescent, which represents a responsive heart. People call them Masters, but they are in reality pupils; for, in point of fact, no one in the world is a Master save God. Man's privilege is to become a greater pupil. Therefore none of the Great Ones have called themselves Masters, nor have they considered themselves to be so. What they have known in their lives is the privilege of opening their hearts wider and wider to reflect the light of the Master, Who is God Himself. The progress of these high Initiates is in their responsiveness, for they have never connected themselves with what they have expressed.