During this ten years he had returned to his native country and to his children, but had not undertaken public duty as a teacher. Now that was forced upon him. The century was drawing to a close. Everywhere there was evident a slackening of religious fervor and faith. A mere external compliance with the rules of Islam was observed, men even openly defended such a course. He adduces as an example of this the _Wasiya_ of Ibn Sina. The students of philosophy went their way, and their conduct shook the minds of the people; false Sufis abounded, who taught antinomianism; the lives of many theologians excited scandal; the Ta‘limites were still spreading. A religious leader to turn the current was absolutely needed, and his friends looked to al-Ghazzali to take up that duty; some distinguished saints had dreams of his success; God had promised a reformer every hundred years and the time was up. Finally, the Sultan laid a command upon him to go and teach in the academy at Naysabur, and he was forced to consent. His departure for Naysabur fell at the end of 499, exactly eleven years after his flight from Baghdad. But he did not teach there long. Before the end of his life we find him back at Tus, his native place, living in retirement among his disciples, in a Madrasa or academy for students and a Khanqah or monastery for Sufis. [Sidenote: THE TAHAFUT] There he settled down to study and contemplation. We have already seen what theological position he had reached. Philosophy had been tried and found wanting. In a book of his called _Tahafut_, or “Destruction,” he had smitten the philosophers hip and thigh; he had turned, as in earlier times al-Ash‘ari, their own weapons against them, and had shown that with their premises and methods no certainty could be reached. In that book he goes to the extreme of intellectual scepticism, and, seven hundred years before Hume, he cuts the bond of causality with the edge of his dialectic and proclaims that we can know nothing of cause or effect, but simply that one thing follows another. He combats their proof of the eternity of the world, and exposes their assertion that God is its creator. He demonstrates that they cannot prove the existence of the creator or that that creator is one; that they cannot prove that He is incorporeal, or that the world has any creator or cause at all; that they cannot prove the nature of God or that the human soul is a spiritual essence. When he has finished there is no intellectual basis left for life; he stands beside the Greek sceptics and beside Hume. We are thrown back on revelation, that given immediately by God to the individual soul or that given through prophets. All our real knowledge is derived from these sources. So it was natural that in the latter part of his life he should turn to the traditions of the Prophet. The science of tradition must certainly have formed part of his early studies, as of those of all