“In the name of the most merciful God.”

Quoth the Imam Ghazzali:

Glory be to God, Whose praise should precede every writing and every speech! May the blessings of God rest on Muhammed His Prophet and His Apostle, on his family and companions, by whose guidance error is escaped!

You have asked me, O brother in the faith, to expound the aim and the mysteries of religious sciences, the boundaries and depths of theological doctrines. You wish to know my experiences while disentangling truth lost in the medley of sects and divergencies of thought, and how I have dared to climb from the low levels of traditional belief to the topmost summit of assurance. You desire to learn what I have borrowed, first of all from scholastic theology; and secondly from the method of the Ta’limites, who, in seeking truth, rest upon the authority of a leader; and why, thirdly, I have been led to reject philosophic systems; and finally, what I have accepted of the doctrine of the Sufis, and the sum total of truth which I have gathered in studying every variety of opinion. You ask me why, after resigning at Bagdad a teaching post which attracted a number of hearers, I have, long afterwards, accepted a similar one at Nishapur. Convinced as I am of the sincerity which prompts your inquiries, I proceed to answer them, invoking the help and protection of God.

Know then, my brothers (may God direct you in the right way), that the diversity in beliefs and religions, and the variety of doctrines and sects which divide men, are like a deep ocean strewn with shipwrecks, from which very few escape safe and sound. Each sect, it is true, believes itself in possession of the truth and of salvation, “each party,” as the Koran saith, “rejoices in its own creed”; but as the chief of the apostles, whose word is always truthful, has told us, “My people will be divided into more than seventy sects, of whom only one will be saved.” This prediction, like all others of the Prophet, must be fulfilled.

From the period of adolescence, that is to say, previous to reaching my twentieth year to the present time when I have passed my fiftieth, I have ventured into this vast ocean; I have fearlessly sounded its depths, and, like a resolute diver, I have penetrated its darkness and dared its dangers and abysses. I have interrogated the beliefs of each sect and scrutinised the mysteries of each doctrine, in order to disentangle truth from error and orthodoxy from heresy. I have never met one who maintained the hidden meaning of the Koran without investigating the nature of his belief, nor a partisan of its exterior sense without inquiring into the results of his doctrine. There is no philosopher whose system I have not fathomed, nor theologian the intricacies of whose doctrine I have not followed out.

Sufism has no secrets into which I have not penetrated; the devout adorer of Deity has revealed to me the aim of his austerities; the atheist has not been able to conceal from me the real reason of his unbelief. The thirst for knowledge was innate in me from an early age; it was like a second nature implanted by God, without any will on my part. No sooner had I emerged from boyhood than I had already broken the fetters of tradition and freed myself from hereditary beliefs.

Having noticed how easily the children of Christians become Christians, and the children of Moslems embrace Islam, and remembering also the traditional saying ascribed to the Prophet, “Every child has in him the germ of Islam, then his parents make him Jew, Christian, or Zoroastrian,” I was moved by a keen desire to learn what was this innate disposition in the child, the nature of the accidental beliefs imposed on him by the authority of his parents and his masters, and finally the unreasoned convictions which he derives from their instructions.

Struck with the contradictions which I encountered in endeavouring to disentangle the truth and falsehood of these opinions, I was led to make the following reflection: “The search after truth being the aim which I propose to myself, I ought in the first place to ascertain what are the bases of certitude.” In the next place I recognised that certitude is the clear and complete knowledge of things, such knowledge as leaves no room for doubt nor possibility of error and conjecture, so that there remains no room in the mind for error to find an entrance. In such a case it is necessary that the mind, fortified against all possibility of going astray, should embrace such a strong conviction that, if, for example, any one possessing the power of changing a stone into gold, or a stick into a serpent, should seek to shake the bases of this certitude, it would remain firm and immovable. Suppose, for instance, a man should come and say to me, who am firmly convinced that ten is more than three, “No; on the contrary, three is more than ten, and, to prove it, I change this rod into a serpent,” and supposing that he actually did so, I should remain none the less convinced of the falsity of his assertion, and although his miracle might arouse my astonishment, it would not instil any doubt into my belief.

I then understood that all forms of knowledge which do not unite these conditions (imperviousness to doubt, etc.) do not deserve any confidence, because they are not beyond the reach of doubt, and what is not impregnable to doubt cannot constitute certitude.