Aristotle’s Cosmology
• Aristotle separated the Universe into two parts.
• The first one is Celestial Region. And the second one sublunary universe: Terrestrial Region.
• There are different laws of nature in these two
universes.
In Celestial Region
• Planets and stars revolve around the World.
• All celestial bodies are made of element aether.
• The natural motion of the aether is the perfect circle.
(Circle Dogma)
• Aether doesn’t changeable.
• Therefor it can’t transform into other elements.
• There is no generation or corruption.
• Celestial region influences terrestrial universe.
• The motion is thus transferred to each next spheres.
Terrestrial Region
• There are two kind of motion in terrestrial region.
• 1- Natural Motion
• 2- Violent Motion
Classical Element Theory
• Aristotle developed Empedocles’ four elements theory more systematically.
• Plato was the first philosopher using the term “element” for these substances.
• Aristotle defined “element” in general his book On the Heaven.
• “An element, we take, is a body into which other bodies
may be analyzed, present in them potentially or in actuality (which is still disputable) and not itself divisible into bodies different in form. That, or something like it, is what all men in every case mean by element”.
You can transform elements from one to another. For example water is wet and cold. But heating of water changes its quality from cold to hot, and thus turns it into air. So, there are generations and corruptions in terrestrial region.
The elements are lined up from heavy to light as follows: Earth, water, air, fire.
Fire: the lightest Air
Water
Earth: the heaviest
