A. _Knowledge._ When the Abstract illumination associates itself with a higher organism, it works out its development by the operation of certain faculties--the powers of light, and the powers of darkness. The former are the five external senses, and the five internal senses--sensorium, conception, imagination, understanding, and memory; the latter are the powers of growth, digestion, etc. But such a division of faculties is only convenient. "One faculty can be the source of all operations."[142:1] There is only one power in the middle of the brain, though it receives different names from different standpoints. The mind is a unity which, for the sake of convenience, is regarded as multiplicity. The power residing in the middle of the brain must be distinguished from the abstract illumination which constitutes the real essence of man. The Philosopher of illumination appears to draw a distinction between the active mind and the essentially inactive soul; yet he teaches that in some mysterious way, all the various faculties are connected with the soul. [142:1] S̱ẖarh Anwāriyya fol. 57b. The most original point in his psychology of intellection, however, is his theory of vision.[142:2] The ray of light which is supposed to come out of the eye must be either substance or quality. If quality, it cannot be transmitted from one substance (eye) to another substance (visible body). If, on the other hand, it is a substance, it moves either consciously, or impelled by its inherent nature. Conscious movement would make it an animal perceiving other things. The perceiver in this case would be the ray, not man. If the movement of the ray is an attribute of its nature, there is no reason why its movement should be peculiar to one direction, and not to all. The ray of light, therefore, cannot be regarded as coming out of the eye. The followers of Aristotle hold that in the process of vision images of objects are printed on the eye. This view is also erroneous; since images of big things cannot be printed on a small space. The truth is that when a thing comes before the eye, an illumination takes place, and the mind sees the object through that illumination. When there is no veil between the object and the normal sight, and the mind is ready to perceive, the act of vision must take place; since this is the law of things. "All vision is illumination; and we see things in God". Berkley explained the relativity of our sight-perceptions with a view to show that the ultimate ground of all ideas is God. The Is̱ẖrāqī Philosopher has the same object in view, though his theory of vision is not so much an explanation of the sight-process as a new way of looking at the fact of vision. [142:2] S̱ẖarh Anwāriyya fol. 60b.