Know that the negative attributes of God are the true attributes: they do not include any incorrect notions or any deficiency whatever in reference to God, while positive attributes imply polytheism, and are inadequate, as we have already shown. It is now necessary to explain how negative expressions can in a certain sense be employed as attributes, and how they are distinguished from positive attributes. Then I shall show that we cannot describe the Creator by any means except by negative attributes. An attribute does not exclusively belong to the one object to which it is related; while qualifying one thing, it can also be employed to qualify other things, and is in that case not peculiar to that one thing.
E.g., if you see an object from a distance, and on enquiring what it is, are told that it is a living being, you have certainly learnt an attribute of the object seen, and although that attribute does not exclusively belong to the object perceived, it expresses that the object is not a plant or a mineral. Again, if a man is in a certain house, and you know what something is in the house, but not exactly what, you ask what is in that house, and you are told, not a plant or a mineral. You have thereby obtained some special knowledge of the thing; you have learnt that it is a living being, although you do not yet know what kind of a living being it is.
The negative attributes have this in common with the positive, that they necessarily circumscribe the object to some extent, although such circumscription consists only in the exclusion of what otherwise would not be excluded. In the following point, however, the negative attributes are distinguished from the positive. The positive attributes, although not peculiar to one thing, describe a portion of what we desire to know, either some part of its essence or some of its accidents; the negative attributes, on the other hand, do not, as regards the essence of the thing which we desire to know, in any way tell us what it is, except it be indirectly, as has been shown in the instance given by us.
Quoted from The Philosopher’s Handbook, ed. Stanley Rosen (Random House: 2000) pp. 135-136