Maimonides, answered from the texts and cited to the page.
The path to speaking rightly of God begins with a recognition that has already been demonstrated: He is existent of necessity, there is no composition in Him, and we are able to apprehend only the fact that He is — we cannot apprehend His quiddity.1 From this single recognition, everything follows. Affirmative attributes fail for a precise reason.
When you predicate something of a thing, you indicate either a part of its substance or one of its accidents. But God has no "That" outside of His "What," His essence is not compound, and He has no accidents — so there is simply nothing for an affirmative attribute to indicate.2 Whatever you name as a perfection and predicate of Him, even if it existed as pertaining to Him, would not belong to the same species of perfection you intend, save only by equivocation.3
Worse: if you say He is a substratum bearing certain attributes — even unknown ones — you have introduced duality into the divine, and duality, followed to its conclusion, yields not monotheism but polytheism.4 Negative attributes escape this trap entirely. They attach no notion of multiplicity to Him, and they conduct the mind toward the utmost reach that man may attain in apprehending Him.5
The procedure runs thus: we apprehend that something exists whose nonexistence is impossible — so we say He exists, meaning His nonexistence is impossible. We apprehend that this being is not like dead bodies — so we say He is living, meaning He is not dead. We apprehend that He is not like the heaven, a living body — so we say He is not a body.6
Each step removes an inadequate likeness; none of them deposits a positive content into the divine essence. The description of God by means of negations is the correct description — one not affected by indulgence in facile language and implying no deficiency.7 Affirmations imply association with what is other than He; negations do not. And the limit of this path is itself instructive.
He is His knowledge and His knowledge is He — the whole is one thing.8 To comprehend His knowledge would be to comprehend His existence, and that is beyond us, not because He is obscure but because His existence is stronger than our intellects, as the light of the sun exceeds the power of vision that turns toward it.9 We know that He knows, just as we know that He exists — and if asked how He is identical with His knowledge, the honest answer is that we do not perceive that, just as we do not perceive His existence perfectly.10
The wise will understand: negative theology is not silence masquerading as method. It is the only method that respects what has actually been demonstrated.
It is consequently impossible that He should have affirmative attributes. For He has no 'That' outside of His 'What,' and hence an attribute cannot be indicative of one of the two.Guide of the Perplexed Vol 1, pp. 268–269
He has no 'That' outside of His 'What,' and hence an attribute cannot be indicative of one of the two; all the more His 'What' is not compound so that an attribute cannot be indicative of its two parts; and all the more, He cannot have accidents so that an attribute cannot be indicative of them.Guide of the Perplexed Vol 1, pp. 270–271
anything that we think of as a perfection—even if it existed as pertaining to Him—in accordance with the opinion of those who believe in the attributes, nevertheless would not belong to the species of perfection that we think of, save only by equivocation.Guide of the Perplexed Vol 1, pp. 279–280
if you say God, may He be exalted, is a certain substratum bearing certain things as adjuncts and that this substratum is not like these adjuncts, the utmost of our apprehension would be, on the basis of this belief, polytheism and nothing else.Guide of the Perplexed Vol 1, pp. 279–280
the attributes of negation do not give us knowledge in any respect whatever of the essence the knowledge of which is sought... no notion of multiplicity can attach to Him in any respect on account of them; and, moreover, they conduct the mind toward the utmost reach that man may attain in the apprehension of Him.Guide of the Perplexed Vol 1, pp. 270–271
We apprehend further that this being is not like the being of the heaven, which is a living body. We say accordingly that He is not a body.Guide of the Perplexed Vol 1, pp. 270–271
the description of God, may He be cherished and exalted, by means of negations is the correct description—a description that is not affected by an indulgence in facile language and does not imply any deficiency with respect to God in general or in any particular mode.Guide of the Perplexed Vol 1, pp. 268–269
He is His knowledge and His knowledge is He. This idea is strange and marvelous, but it eluded them so they perished.Eight Chapters, pp. 35–36
The inadequacy of our intellects to perceive Him is like the inadequacy of the light of [our] vision to perceive the light of the sun. That is not due to the weakness of the light of the sun, but to the latter being stronger than the light [of vision] which wants to perceive it.Eight Chapters, pp. 35–36
we know that He knows, just as we know that He exists. So if we are asked how He is identical with His knowledge, we shall say that we do not perceive that, just as we do not perceive His existence perfectly.Eight Chapters, pp. 35–36