Each stage is marked by more or less intense illuminations, which are accompanied by some indescribable sounds. Death does not put an end to the spiritual progress of the soul. The individual souls, after death, are not unified into one soul, but continue different from each other in proportion to the illumination they received during their companionship with physical organisms. The Philosopher of illumination anticipates Leibniz's doctrine of the Identity of Indiscernibles, and holds that no two souls can be completely similar to each other.[147:1] When the material machinery which it adopts for the purpose of acquiring gradual illumination, is exhausted, the soul probably takes up another body determined by the experiences of the previous life; and rises higher and higher in the different spheres of being, adopting forms peculiar to those spheres, until it reaches its destination--the state of absolute negation. Some souls probably come back to this world in order to make up their deficiencies.[147:2] The doctrine of trans-migration cannot be proved or disproved from a purely logical standpoint; though it is a probable hypothesis to account for the future destiny of the soul. All souls are thus constantly journeying towards their common source, which calls back the whole Universe when this journey is over, and starts another cycle of being to reproduce, in almost all respects, the history of the preceding cycles. [147:1] S̱ẖarh Anwāriyya fol. 82. [147:2] S̱ẖarh Anwāriyya fol. 87b.