Guide for the Perplexed, by Moses Maimonides, Friedländer tr. [1904], at sacred-texts.com
THERE are many things whose existence is manifest and obvious; some of these are innate notions or objects of sensation, others are nearly so: and in fact they would require no proof if man had been left in his primitive state. Such are the existence of motion, of man's free will, of phases of production and destruction, and of the natural properties perceived by the senses, e.g., the heat of fire, the coldness of water, and many other similar things. False notions, however, may be spread either by a person labouring under error, or by one who has some particular end in view, and who establishes theories contrary to the real nature of things, by denying the existence of things perceived by the senses, or by affirming the existence of what does not exist. Philosophers are thus required to establish by proof things which are self-evident, and to disprove the existence of things which only exist in man's imagination. Thus Aristotle gives a proof for the existence of motion, because it had been denied: he disproves the reality of atoms, because it had been asserted.
To the same class belongs the rejection of essential attributes in reference to God. For it is a self-evident truth that the attribute is not inherent in the object to which it is ascribed, but it is superadded to its essence, and is consequently an accident; if the attribute denoted the essence [τὸ τῒ ἦν εἶναι] of the object, it would be either mere tautology, as if, e.g., one would say "man is man," or the explanation of a name, as, e.g., "man is a speaking animal"; for the words "speaking animal" include the true essence of man, and there is no third element besides life and speech in the definition of man; when he, therefore, is described by the attributes of life and speech, these are nothing but an explanation of the name "man," that is to say, that the thing which is called man, consists of life and speech. It will now be clear that the attribute must be one of two things, either the essence of the object described--in that case it is a mere explanation of a name, and on that account we might admit the attribute in reference to God, but we reject it from another cause as will be shown--or the attribute is something different
from the object described, some extraneous superadded element; in that case the attribute would be an accident, and he who merely rejects the appellation "accidents" in reference to the attributes of God, does not thereby alter their character: for everything superadded to the essence of an object joins it without forming part of its essential properties, and that constitutes an accident. Add to this the logical consequence of admitting many attributes, viz., the existence of many eternal beings. There cannot be any belief in the unity of God except by admitting that He is one simple substance, without any composition or plurality of elements: one from whatever side you view it, and by whatever test you examine it: not divisible into two parts in any way and by any cause, nor capable of any form of plurality either objectively or subjectively, as will be proved in this treatise.
Some thinkers have gone so far as to say that the attributes of God are neither His essence nor anything extraneous to His essence. This is like the assertion of some theorists, that the ideals, i.e., the universalia, are neither existing nor non-existent, and like the views of others, that the atom does not fill a definite place, but keeps an atom of space occupied; that man has no freedom of action at all, but has acquirement. Such things are only said: they exist only in words, not in thought, much less in reality. But as you know, and as all know who do not delude themselves, these theories are preserved by a multitude of words, by misleading similes sustained by declamation and invective, and by numerous methods borrowed both from dialectics and sophistry. If after uttering them and supporting them by such words, a man were to examine for himself his own belief on this subject, he would see nothing but confusion and stupidity in an endeavour to prove the existence of things which do not exist, or to find a mean between two opposites that have no mean. Or is there a mean between existence and non-existence, or between the identity and non-identity of two things? But, as we said, to such absurdities men were forced by the great licence given to the imagination, and by the fact that every existing material thing is necessarily imagined as a certain substance possessing several attributes; for nothing has ever been found that consists of one simple substance without any attribute. Guided by such imaginations, men thought that God was also composed of many different elements, viz., of His essence and of the attributes superadded to His essence. Following up this comparison, some believed that God was corporeal, and that He possessed attributes: others, abandoning this theory, denied the corporeality, but retained the attributes. The adherence to the literal sense of the text of Holy Writ is the source of all this error, as I shall show in some of the chapters devoted to this theme.