Aristotle's Theory Of Motion

In Book 8 of Physics, Aristotle attempts to account for the origin of motion in the universe . Before providing his own theory, Aristotle first reflects on accounts given by previous philosophers. He considers Anaxagoras, who believed all things were at rest for an infinite period of time until mind introduced motion and separated them (Phys. 8.1, 250b25); Empedocles, who held that the universe is in a continuous cycle of motion and rest (Phys. 8.1, 250b26-28); and Democritus, who maintained that since things happen in the past as they do now, motion must have always existed (Phys. 8.1, 252a34-35).

Aristotle rejects Anaxagoras’ theory on the basis that if things were at rest until at some point in time motion was initiated, this particular

8.5, 256a3-5), Aristotle puts forth his own account for the origin of motion. He asks us to consider the case of a man moving a stone with a stick. The man moves his hand, which moves the stick, which moves the stone. Thus, hand, stick and stone are not the authors of their motion, but rather are moved by something else; thus making them moved movers (______). In this way, these moved movers form a causal series, where each acts as an intermediary between the thing that moves them and the thing they move (Phys. 8.5, 256a5-10). However, Aristotle states that it is impossible for such a causal series to regress infinitely (______); rather, there must be something that is both a mover and not moved by something else in order to initiate the series; i.e. a first mover (Phys. 8.5, 256a16). In this case, the first mover is the man. While the man causes motion in something else, he himself is not moved by some other thing, rather he is the author of his own motion, thus making him the first mover in the series. Similarly, argues Aristotle, the motion of the cosmos must owe its origin to a first mover, i.e. a mover that isn’t moved by any other thing