Aristotle's Physics
Concepts
Aristotle's physics describes a hierarchical cosmos with spheres carrying celestial bodies orbiting around a central Earth. The universe is divided into two spheres: the terrestrial (changeable) and the celestial (unchanging).
Elements and Spheres
Four elements (earth, air, fire, water) compose the terrestrial spheres, which are subject to change. The celestial spheres are made of an unchangeable element called "aether."
Celestial Spheres
Celestial bodies, including the Sun, Moon, and planets, are embedded in concentric spheres that rotate eternally. The outermost sphere, carrying fixed stars, is unmoved and serves as a "prime mover."
Terrestrial Change
Earthly elements have "natural motions": heavy elements like earth and water fall, while lighter elements like air and fire rise. Changes in elements occur when they transform into another element that shares a property.
Natural Place
Aristotle believed that each element has a "natural place" in the cosmos. Heavy elements naturally move towards the center, while lighter elements move away from it.
Natural Motion
Objects move at speeds proportional to their weights and inversely proportional to the resistance of the medium. In a vacuum, objects would move indefinitely fast.
Unnatural Motion
Motion against these natural tendencies is caused by external forces. Aristotle proposed the concept of "impetus," a force that keeps objects moving even after the initial force is applied.
Chance
Aristotle recognized accidents that occur without a specific cause, which he termed "chance."
Continuum and Vacuum
Aristotle argued that a vacuum cannot exist. If it did, objects moving within it would accelerate indefinitely.
Four Causes
Aristotle identified four causes for change:
- Material: The matter of which something is made
- Formal: The essential property that defines its nature
- Efficient: The primary agency that gives it form
- Final: The purpose or aim of its existence
Biology
Aristotle's biology focused on the study of natural kinds, their differentiation, and their causes. He believed organisms have natural forms that guide their development and functioning.
Medieval Commentary
Aristotle's physics faced criticism and modifications in the Middle Ages, including the introduction of the concept of "inertia," which suggested that objects in motion tend to remain in motion.
Life and Death of Aristotelian Physics
Aristotle's physics dominated for centuries but was gradually discredited by the work of scientists like Galileo and Newton. However, it remained influential as a scholastic pursuit until the 17th century.
Modern Evaluations
Modern scholars debate whether Aristotle's physics was truly scientific, as it relied heavily on philosophical speculation rather than empirical observation.