Ancient Greek Physics: Aristotle's Causes & Pre-Socratic Thought

Aristotelian Physics: Change, Causes, and the Prime Mover

The study of Physics, in the Aristotelian sense, is the science of mobile entities. It explains change and evolution, detailing how they are produced by Potency [what is not but "can" become] and Act [what it is]. Change is the transition from what is potential to what is actual (to become something).

• Substantial Change: A transformation in the very nature of a thing (e.g., from a seed to a tree).
• Accidental Change: A transformation in a non-essential quality (e.g., from a student to a doctor). Accidental changes can be:
  • Quantitative (change in size or number)
  • Qualitative (change in quality or characteristic)
  • Locative (change in place or position)

Matter is defined as the potential to be shaped and formed. Any change in matter must have a subject that undergoes it.

Theory of the Four Causes

Knowing something, according to Aristotle, involves understanding its causes. According to hylomorphism, substances are composed of matter and form, relating to the material cause and formal cause. However, when explaining natural beings, one must also consider the causes that originate motion and purpose:

• Material Cause: That out of which something is made (e.g., clay for a vase).
• Efficient Cause: That by which something is made or changed (e.g., the artisan for a vase).
• Formal Cause: The essence or design of a thing (e.g., the engravings representing the design of a vase).
• Final Cause: The purpose or end for which something exists (e.g., to contain flowers for a vase).

In artificial objects, these causes are clearly identifiable. In natural phenomena, the final cause often coincides with the formal and efficient causes.

The Prime Mover

The need for a Prime Mover arises from Aristotle's attempt to explain the origin of all motion. He believed that whatever moves is moved by a motor, which in turn is moved by another, and so on. To avoid infinite regress, he posited a First Mover: eternal, immaterial, and pure act. If it were not pure act, it would have potential, and its movement would need to be explained by an external agent. This Prime Mover is understood as a final cause.

This concept marks the boundary of physics, leading to the philosophical study of being par excellence – the cause of all motion, which Aristotle identified with God. Therefore, Aristotle held a theological conception of nature, contrasting with mechanistic views.

Key Concepts in Ancient Natural Philosophy

Teleology

Concepts that consider nature as tending towards an end or purpose.

Mechanism

The view that natural phenomena operate under mechanical conditions, and their source is often attributed to chance rather than purpose.

Pre-Socratic Natural Philosophy

Monists

These philosophers sought a single, fundamental principle (arche) from which everything originated:

• Thales: Proposed Water as the fundamental substance.
• Anaximander: Proposed Apeiron (the Indeterminate) as the boundless origin.
• Anaximenes: Proposed Air, through rarefaction and condensation, as the primary element.

Pluralists

These philosophers proposed multiple fundamental elements or principles:

Empedocles

Proposed the four roots (earth, air, fire, water) as essences, with Aether as a fifth essence. These elements are governed by two opposing forces: Love [attraction] and Strife [repulsion]. He conceived of linear time organized into a cosmic cycle or 'Great Year' with four stages:

• Two polar stages (predominance of Love or Strife).
• Two transitional (mixed) stages.

Mixed stages occur randomly, resulting in individuals that are sometimes viable and sometimes not.

Democritus

Believed in atoms as the minimal, irreducible units. Between them is the void. The only source of motion is the atoms themselves. Through their movement, clashes occur, generating motion governed by relentless mechanical necessity. This led to the concept of mechanical laws.

Anaxagoras

Proposed Homeomeries as tiny, irreducible portions of matter, identified as containing the germ or seed qualities of all natural objects. The Nous (Mind) is the discerning force that acts upon the homeomeries, separating them and imparting motion to matter.