I proceeded from the study of scholastic theology to that of philosophy. It was plain to me that, in order to discover where the professors of any branch of knowledge have erred, one must make a profound study of that science; must equal, nay surpass, those who know most of it, so as to penetrate into secrets of it unknown to them. Only by this method can they be completely answered, and of this method I can find no trace in the theologians of Islam. In theological writings devoted to the refutation of philosophy I have only found a tangled mass of phrases full of contradictions and mistakes, and incapable of deceiving, I will not say a critical mind, but even the common crowd. Convinced that to dream of refuting a doctrine before having thoroughly comprehended it was like shooting at an object in the dark, I devoted myself zealously to the study of philosophy; but in books only and without the aid of a teacher. I gave up to this work all the leisure remaining from teaching and from composing works on law. There were then attending my lectures three hundred of the students of Bagdad. With the help of God, these studies, carried on in secret, so to speak, put me in a condition to thoroughly comprehend philosophical systems within a space of two years. I then spent about a year in meditating on these systems after having thoroughly understood them. I turned them over and over in my mind till they were thoroughly clear of all obscurity. In this manner I acquired a complete knowledge of all their subterfuges and subtleties, of what was truth and what was illusion in them. I now proceed to give a resumé of these doctrines. I ascertained that they were divided into different varieties, and that their adherents might be ranged under diverse heads. All, in spite of their diversity, are marked with the stamp of infidelity and irreligion, although there is a considerable difference between the ancient and modern, between the first and last of these philosophers, according as they have missed or approximated to the truth in a greater or less degree. CONCERNING THE PHILOSOPHICAL SECTS AND THE STIGMA OF INFIDELITY WHICH ATTACHES TO THEM ALL The philosophical systems, in spite of their number and variety, may be reduced to three: (1) The Materialists; (2) The Naturalists; (3) The Theists. (1) _The Materialists._ They reject an intelligent and omnipotent Creator and Disposer of the Universe. In their view the world exists from all eternity and had no author. The animal comes from semen and semen from the animal; so it has always been and will always be; those who maintain this doctrine are atheists.