The dominant concept in Aristotle's philosophy of nature is his notion of causation. ...The final cause states that each substance has an inherent pu… - John Freely

John Philoponus (c. 490-570) of Alexandria... refuted Aristotle's theory that the velocities of falling bodies in a given medium are proportional to their weight, making the observation that "if one lets fall simultaneously from the same height two bodies differing greatly in weight, one will find that the ratio of the times of their motion does not correspond to the ratios of their weights, but the difference in time is a very small one." …He also criticized Aristotle's antiperistasis theory of projectile motion, which states that the air displaced by the object flows back to push it from behind. Instead Philoponus concluded that "some incorporeal kinetic power is imparted by the thrower to the object thrown" and that "if an arrow or a stone is projected by force in a void, the same will happen much more easily, nothing being necessary except the thrower." This is the famous "impetus theory," which was revived in medieval Islam and again in fourteenth century Europe, giving rise to the beginning of modern dynamics.

The atomic theory was not generally accepted in the time of Democritus, largely because of its deterministic character, for it allows no chance, choice, or free will.

Anaxagoras of Clazomenae (0. 500—428 BC) postulated another element called the aether, which was in constant rotation and carried with it the celestial bodies. He also believed that there was a directing intelligence in nature that he called Nous which gives order to what otherwise would be a chaotic universe. By Nous he meant literally "the Mind of the Cosmos"… Anaxagoras was the last of the Ionian physicists.