The second danger threatens those who accept the opinions of the philosophers. When, for instance, we read the "Treatise of the Brothers of Purity," and other works of the same kind, we find in them sentences spoken by the Prophet and quotations from the Sufis. We approve these works; we give them our confidence; and we finish by accepting the errors which they contain, because of the good opinion of them with which they have inspired us at the outset. Thus, by insensible degrees, we are led astray. In view of this danger the reading of philosophic writings so full of vain and delusive utopias should be forbidden, just as the slippery banks of a river are forbidden to one who knows not how to swim. The perusal of these false teachings must be prevented just as one prevents children from touching serpents. A snake-charmer himself will abstain from touching snakes in the presence of his young child, because he knows that the child, believing himself as clever as his father, will not fail to imitate him; and in order to lend more weight to his prohibition the charmer will not touch a serpent under the eyes of his son. Such should be the conduct of a learned man who is also wise. But the snake-charmer, after having taken the serpent and separated the venom from the antidote, having put the latter on one side and destroyed the venom, ought not to withhold the antidote from those who need it. In the same way the skilled coin-assayer, after having put his hand in the bag of the false coiner, taken out the good coins and thrown away the bad ones, ought not to refuse the good to those who need and ask for it. Such should be the conduct of the learned man. If the patient feels a certain dislike of the antidote because he knows that it is taken from a snake whose body is the receptacle of poison, he should be disabused of this fallacy. If a beggar hesitates to take a piece of gold which he knows comes from the purse of a false coiner, he should be told that his hesitation is a pure mistake which would deprive him of the advantage which he seeks. It should be proved to him that the contact of the good coins with the bad does not injure the former and does not improve the latter. In the same way the contact of truth with falsehood does not change truth into falsehood, any more than it changes falsehood into truth. Thus much, then, we have to say regarding the inconveniences and dangers which spring from the study of philosophy. _Sufism_ When I had finished my examination of these doctrines I applied myself to the study of Sufism. I saw that in order to understand it thoroughly one must combine theory with practise. The aim which the Sufis set before them is as follows: To free the soul from the tyrannical yoke of the passions, to deliver it from its wrong inclinations and evil instincts, in order that in the purified heart there should only remain room for God and for the invocation of his holy name.