Guide for the Perplexed, by Moses Maimonides, Friedländer tr. [1904], at sacred-texts.com
WE have already, on several occasions, shown in this treatise that everything that implies corporeality or passiveness, is to be negatived in reference to God, for all passiveness implies change: and the agent producing that state is undoubtedly different from the object affected by it; and if God could be affected in any way whatever, another being beside Him would act on Him and cause change in Him. All kinds of non-existence must likewise be negatived in reference to Him: no perfection whatever can therefore be imagined to be at one time absent from Him, and at another present in Him: for if this were the case, He would [at a certain time] only be potentially perfect. Potentiality always implies non-existence, and when anything has to pass from potentiality into reality, another thing that exists in reality is required to effect that transition. Hence it follows that all perfections must really exist in God, and none of them must in any way be a mere potentiality. Another thing likewise to be denied in reference to God, is similarity to any existing being. This has been generally accepted, and is also mentioned in the books of the Prophets: e.g., "To whom, then, will you liken me?" (Isa. xl. 25); "To whom, then, will you liken God?" (ib. 18); "There is none like unto Thee" (Jer. x. 6). Instances of this kind are frequent. In short, it is necessary to demonstrate by proof that nothing can be predicated of God that implies any of the following four things: corporeality, emotion or change, nonexistence,--e.g., that something would be potential at one time and real at another--and similarity with any of His creatures. In this respect our knowledge of God is aided by the study of Natural Science. For he who is ignorant of the latter cannot understand the defect implied in emotions, the difference between potentiality and reality, the non-existence implied in all potentiality, the inferiority of a thing that exists in potentiâ to that which moves in order to cause its transition from potentiality into reality, and the
inferiority of that which moves for this purpose compared with its condition when the transition has been effected. He who knows these things, but without their proofs, does not know the details which logically result from these general propositions: and therefore he cannot prove that God exists, or that the [four] things mentioned above are inadmissible in reference to God.
Having premised these remarks, I shall explain in the next chapter the error of those who believe that God has essential attributes: those who have some knowledge of Logic and Natural Science will understand it.