He argues against the theory of Aristotle that the soul of man is his thought and that only the soul of the philosopher will be united, after the death of the body, with the active intellect. "Is there," he asks, "any curriculum of the knowledge one has to acquire to win immortality? How is it that the soul of one man differs from that of another? How can one forget a thing once thought of?" and many other questions of the kind. He shows himself especially severe against the Motekallamin, whose arguments on the creation of the world, on God and His unity, he terms dialectic exercises and mere phrases.