Aristotle vs Plato: The Nature of Reality and Change

Plato and Aristotle on the Nature of Reality

For Plato, authentic reality was an immutable and perfect world of ideas. The world around us is only an imperfect and corrupt copy of these ideas; therefore, we know them only if we understand what we see through these forms. For Plato, ideas are what make the physical world intelligible because they constitute the essence of things. Aristotle, however, finds the existence of perfect ideas for everything bad and negative in the world to be inadmissible. For Aristotle, the essence of things and their 'why' cannot be separated from the things themselves.

The Problem of Movement and Change

Aristotle finds a flaw in Plato's ideal theory: it fails to explain or give reasons for what is most characteristic of the material and sensitive world, which is movement and change.

The Synthesis of Platonic Theory

The Platonic theory suppose a synthesis of two theories. On one hand, we have the sensible world, characterized by a constant process of transformation (as Heraclitus described). On the other hand, there is the perfect abstract world of ideas, characterized by immortality and eternity (as Parmenides described). However, according to Aristotle, Plato only juxtaposed the two concepts but failed to integrate them. This is why Aristotle did not consider Plato's response an authentic explanation of nature and change.

Aristotle's Physics and Metaphysics

To understand Aristotle's defense, we must enter his Physics (the science of being in motion) and his Metaphysics. To understand his explanation of change, we must first know his conception of reality.

Aristotelian Cosmology and the Two Worlds

Aristotle said that the world was divided into two parts and the only center was the Earth, followed by two areas that held the stars and planets.

The Sublunary World

The sublunary world (the terrestrial world) extends from the moon downwards. Its characteristics include:

• Elements: Composed of four elements (as defined by Empedocles): air, water, earth, and fire.
• Movements:
  • Natural: Every body tends to go toward its corresponding natural layer.
  • Violent: Movement that is not natural or is against nature.
• The Projectile Problem: This problem remained open for many centuries regarding bodies in violent movement that continue moving after having lost touch with their propulsor.
• Nature: It is imperfect and corruptible.

The Supralunary World

The supralunary world (the celestial world) extends from the moon upwards. Its characteristics include:

• Elements: Formed by a fifth element called ether, which is an element that does not wear out.
• Nature: Perfect and incorruptible.
• Movements: Circular, perfect, and unchanging, occurring at a stable speed.
• The Spheres: This explains the recession of the planets and the motions of the planets across the constellations, with each planet occupying one sphere.