The book by which his name has lived, and which has had strange haps, is the romance of _Hayy ibn Yaqzan_, “The Living One, Son of the Waking One.” In it he conceives two islands, the one inhabited and the other not. On the inhabited island we have conventional people living conventional lives, and restrained by a conventional religion of rewards and punishments. Two men there, Salaman and Asal, have raised themselves to a higher level of self-rule. Salaman adapts himself externally to the popular religion and rules the people; Asal, seeking to perfect himself still further in solitude, goes to the other island. But there he finds a man, Hayy ibn Yaqzan, who has lived alone from infancy and has gradually, by the innate and uncorrupted powers of the mind, developed himself to the highest philosophic level and reached the Vision of the Divine. He has passed through all the stages of knowledge until the universe lies clear before him, and now he finds that his philosophy thus reached, without prophet or revelation, and the purified religion of Asal are one and the same. The story told by Asal of the people of the other island sitting in darkness stirs his soul and he goes forth to them as a missionary. But he soon learns that the method of Muhammad was the true one for the great masses, and that only by sensuous allegory and concrete things could they be reached and held. He retires to his island again to live the solitary life. The bearing of this on the system of the Muwahhids cannot be mistaken. If it is a criticism of the finality of historical revelation, it is also a defence of the attitude of the Muwahhids toward both people and philosophers. By the favor of Abu Ya‘qub, Ibn Tufayl had practically been able to live on an island and develop himself by study. So, too, Abu Ya‘qub might stand for the enlightened but practical Salaman. Yet the meaning evidently is that between them they failed and must fail. There could only be a solitary philosopher here and there, and happy for him if he found a princely patron. The people which knew not the truth were accursed. Perhaps, rather, they were children and had to be humored and guided as such in an endless childhood.