He is considered to be a pioneer of the methods of doubt and skepticism, and in one of his major works, "The Incoherence of the Philosophers", he changed the course of early Islamic philosophy. He changed the early Islamic philosophy away from an Islamic metaphysics influenced by ancient Greek and Hellenistic philosophy. The new way was towards an Islamic philosophy based on cause-and-effect that was determined by God or intermediate angels, a theory now known as occasionalism.