based on lectures given by Ammonius, but gradually he established his own independent thinking in his commentaries and critiques of Aristotle's On the Soul and Physics. In the latter work Philoponus became one of the earliest thinkers to reject Aristotle's dynamics and propose the "theory of impetus": i.e., an object moves and continues to move because of an energy imparted in it by the mover and ceases the movement when that energy is exhausted. This insightful theory was the first step towards the concept of inertia in modern physics, although Philoponus' theory was largely ignored at the time because he was too radical in his rejection of Aristotle. Philoponus is the only writer of antiquity to have formally presented such a concept. As the discovery of the principle of inertia is the hallmark achievement of modern science as it emerges in the 16th to 17th centuries, Pierre Duhem argues that its invention would put Philoponus among the "great geniuses of Antiquity" and the "principal precursors to modern science", although he holds it more likely that Philoponus may have received the idea from an earlier, otherwise unrecorded Alexandrian school of mechanics. In 529 Philoponus wrote his critique On the Eternity of the World Against Proclus in which he systematically defeats every argument put forward for the eternity of the world, a theory which formed the basis of pagan attack of the Christian doctrine of Creation. The intellectual battle against eternalism became one of Philoponus' major preoccupations and dominated several of his publications (some now lost) over the following decade. He introduced a new period of scientific thought based heavily on three premises: (1) The universe is a product of one single God, (2) the heavens and the earth have the same physical properties, (3) and the stars are not divine. With these principles Philoponus went after his rival, Simplicius of Cilicia, by questioning Aristotle's' view of dynamics and cosmology. He argued that motion can occur in a void and that the velocity of a falling object is not based on its weight. He also held that God created all matter with its physical properties and with natural laws that would allow matter to progress from a state of chaos to an organized state forming the present universe. What remains of his writings indicate that he used the same didactic methods of reasoning that modern science uses and that he performed genuine