Philosophy in classical Greece is the ultimate origin of the western conception of the nature of a thing. The philosophical study of human nature itself originated, according to Aristotle at least, with Socrates, who turned philosophy from study of the heavens to study of the human things.[3] Socrates is said to have studied the question of how a person should best live, but he left no written works. It is clear from the works of his students Plato and Xenophon, and also what was said by Aristotle (Plato's student) about him, that Socrates was a rationalist and believed that the best life and the life most suited to human nature involved reasoning. The Socratic school was the dominant surviving influence in philosophical discussion in the Middle Ages, amongst Islamic, Christian, and Jewish philosophers.