"'Perhaps,' said I, 'there is no assurance but in the notions of reason, that is to say, first principles, as that ten is more than three; the same thing cannot have been created and yet have existed from all eternity; to exist and not to exist at the same time is impossible.' [Sidenote: Fallibility of reason.] "Upon this the senses replied, 'What assurance have you that your confidence in reason is not of the same nature as your confidence in us? When you relied on us, reason stepped in and gave us the lie; had not reason been there, you would have continued to rely on us. Well, may there not exist some other judge superior to reason, who, if he appeared, would refute the judgments of reason in the same way that reason refuted us? The non-appearance of such a judge is no proof of his non-existence.' [Sidenote: The nature of dreams.] "I strove in vain to answer the objection, and my difficulties increased when I came to reflect on sleep. I said to myself, 'During sleep, you give to visions a reality and consistence, and you have no suspicion of their untruth. On awakening, you are made aware that they were nothing but visions. What assurance have you that all you feel and know when you are awake does actually exist? It is all true as respects your condition at that moment; but it is nevertheless possible that another condition should present itself which should be to your awakened state that which to your awakened state is now to you sleep; so that, as respects this higher condition, your waking is but sleep.'" It would not be possible to find in any European work a clearer statement of the scepticism to which philosophy leads than what is thus given by this Arabian. Indeed, it is not possible to put the argument in a more effective way. His perspicuity is in singular contrast with the obscurity of many metaphysical writers. [Sidenote: Intellectual despair.] "Reflecting on my situation, I found myself bound to this world by a thousand ties, temptations assailing me on all sides. I then examined my actions. The best were those relating to instruction and education, and even there I saw myself given up to unimportant sciences, all useless in another world. Reflecting on the aim of my teaching, I found it was not pure in the sight of the Lord. I saw that all my efforts were directed toward the acquisition of glory to myself. Having, therefore, distributed my wealth, I left Bagdad and retired into Syria, where I remained two years in solitary struggle with my soul, combating my passions, and exercising myself, in the purification of my heart and in preparation for the other world."