There are besides certain passages in the Bible which while having an acceptable meaning when taken literally, contain besides a deeper signification which the practiced eye can detect. Thus in the description of the harlot in the seventh chapter of Proverbs there is beside the plain meaning of the text, the doctrine of matter as the cause of corporeal desires. The harlot, never faithful to one man, leaving one and taking up with another, represents matter which, as Aristotle conceives it, never is without form and constantly changes one form for another. There is really nothing new in this, and Philo apart, whom Maimonides did not know, Ibn Daud anticipated Maimonides here also in making use of the term "homonym" as the basis of this method of interpretation.[252] But whereas Ibn Daud relegates the chapter treating of this principle to a subordinate place, his interest being as he tells us primarily ethical--to solve the problem of free will; Maimonides places it in the very centre of his system. The doctrine of attributes as leading to a true conception of God,--of God as absolutely incorporeal and without any resemblance or relation whatsoever to anything else--is the very keystone of Maimonides's philosophical structure. His purpose is to teach a spiritual conception of God. Anything short of this is worse than idolatry. He cannot reconcile the Bible to such a view without this "homonymic" tool. Hence the great importance of this in his system; and he actually devotes the greater part of the first book of the "Guide" to a systematic and exhaustive survey of all terms in the Bible used as homonyms.[253] All this is preparatory to his discussion of the divine attributes. This consideration will account also for the fact that, systematic and logical thinker as he was, he perpetrates what might appear at first sight as a logical blunder. Instead of first proving the existence of God and then discussing his nature and attributes, as Saadia, Bahya, Ibn Daud and others did before him, he treats exhaustively of the divine attributes in the first book, whereas the proof of the existence of God does not appear until the second book. This inversion of the logical order is deliberate. Maimonides's method is directed _ad hominem_. The Jews for whom he wrote his "Guide" did not doubt the existence of God. But a great many of them had an inadequate idea of his spiritual nature. And apparently the Bible countenanced their anthropomorphism. Hence Maimonides cast logical considerations to the wind, and dealt first with that which was nearest to his heart. The rest could wait, this could not.