Ontología (física y metafísica) y epistemología de Aristóteles
Aristotle's epistemology and ontology: his critic to Plato's philosophy.
Ontology: Physics
Four elements + Ether; The natural place rule: Each of the four terrestrial elements move toward their natural place defining their natural motion (smoke is mainly air, it rises toward the sky but not as high as fire). Bodies move toward their natural place. Earth, that is placed being the center of the universe; next comes water . The natural place of air is, somehow being simimilar to a concentric shell surrounding water. Finally, the natural place of fire is higher than that of air but below the innermost celestial sphere (that carrying the Moon). Heavens are made of a specia fifth element denominated "aether", which is weightless and "incorruptible" (it doesn't change)