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Philoponus ’ early writings are 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 movement when that energy is exhausted.

In this erroneous but insightful theory can be found 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.