How Did Aristotle Think That It Must Occur Due To An External Cause?

In Physics II. 1, Aristotle includes the four well-known simple bodies or elements of earth, fire, air, and water among the natural existing things that have an internal principle of motion and rest. Animals, their parts and plants are also placed by him within the same category in respect of having an intrinsic capability to move themselves. In Physics VIII. 4, however, it seems that Aristotle is suggesting something different than the view that he has posited in Physics II.1. There he argues that simple bodies are not self-movers, and their cause of motion must be external to them. Aristotle, for instance, asserts that if the upward movement of a light thing and the downward movement of a heavy thing are caused by themselves, then why these things cannot move themselves toward the opposite directions of their proper places without being externally forced. To be more specific, Aristotle asks why fire does not move downward or why earth does not move upward by themselves. He then concludes that unlike living bodies like animals, these four elements are not capable of being moved by themselves. Aristotle “seemingly” contradicts himself for the line that he draws between the animal and the elemental motions in Physics VIII. 4. …show more content…
How could he consider the elemental motion natural while he clearly states that it must occur due to an external cause? To answer this question, it is necessary to address the following questions first: What does Aristotle mean by the nature and self-motion? Why, unlike animals, the light and heavy things (i.e. elements) are not self-movers? If they are not capable of moving themselves and still are moved naturally, then what is the source of their motion? Aristotle concludes that although elements are not self-movers, they are moved by something which actualizes their potentiality for