So if we take the eye to be endowed with the power of seeing, then it is not possible except under very limited conditions. These are three in number-light, the intervention of a transparent body between the eye and the object seen, and the possession of necessary colours by the object. A refutation of these conditions in the eyes is also a refutation of those primary principles of knowledge which are known to all. It would be a refutation of the sciences of philosophy and mathematics. The Asharites also maintain that one of the conditions as we have said, for example, is that every rational being has a life, it being apparent in the visible world as a condition for knowledge. Hence we say to them that these are also conditions for seeing things in the visible world. So according to their own principle is the case of the visible and the invisible. In his book _Al Maqasid_ Abu Hamid (Al Ghazzali) intended to oppose the premise that every object perceivable must be in some direction to the one seeing it. He says that a man sees himself reflected in a mirror and sees himself not in any other direction but the opposite one. Hence he can see his self in an opposite direction too. But this is a mistake, because what he sees is not his self but only an image of it. This image is in the opposite direction, being in the mirror, placed there. Of the arguments which they advance to prove the vision of an object having no body, two are famous ones. Of these the more famous is one which says that an object seen is either because it has some colour, or because it has a body, or it is a colour, or because it is existent. Sometimes they mention many other causes than really do exist. They say that it is wrong to suppose that it must be a body, otherwise, no colour would be visible, it being also incorrect to suppose the space to be the colour. Now when all the kinds of suppositions in the premise have been refuted we shall have to believe that only an existent object will be seen. The mistake in this statement is quite clear. For an object is visible because of itself. This is the case with the colour and the body: the colour being visible by itself, and the body through the colour. That is why a thing which has no colour cannot be seen. Had the existence of a thing been the only condition of visibility, it would have been possible to see the sound and the senses. In that case seeing, hearing, in fact all the five senses would have been only one, which is quite contrary to our reason. This problem and others like it have obliged the Mutakallimun to admit that it is possible to _hear_ the colour, and _see_ the sounds. But this is against nature, as man has understood it to be. For it is absolutely evident that the sense of seeing is quite different from that of hearing. Their actions are quite distinct from one another, and the organ of the one cannot work as the organ of the other. It is just as impossible to turn hearing as to turn colour into sound.