Week 2 — Pre-Ptolemaic Astronomy and Aristotle¶
Early Greek Astronomy¶
Goal¶
Explain the motion of celestial bodies through mathematical models.
Key Assumptions¶
- Earth is at the center of the universe.
- Celestial motion must be circular because circles are perfect.
- The heavens are fundamentally different from the Earth.
Philosophical Significance¶
Greek astronomy reflects an early attempt to reconcile:
- mathematical elegance
- empirical observation
The goal was not necessarily physical truth but saving the appearances, meaning constructing mathematical systems that reproduce observed motion.
This raises a philosophical question still debated today:
Are scientific theories meant to describe reality or merely to predict phenomena?
This debate later appears in modern philosophy as:
- instrumentalism (theories are tools for prediction)
- scientific realism (theories describe real structures of the world)
Aristotle — Natural Philosophy¶
Cosmology¶
Aristotle divides the universe into two fundamentally different regions.
Sublunar world
- Earth, water, air, fire
- Subject to change and decay
Superlunar world
- Perfect celestial spheres
- Eternal and unchanging
- Composed of aether
Theory of Motion¶
Natural motion Objects move toward their natural place.
Examples
- Heavy objects move toward Earth.
- Fire moves upward.
Violent motion Motion imposed by external force.
Teleology¶
Aristotle explains natural processes in terms of purposes or ends.
Example Seeds grow into plants because their nature directs them toward that outcome.
Philosophical Significance¶
Aristotle's system represents a deeply integrated worldview.
Science was not separate from metaphysics. It involved:
- explanation of causes
- understanding of purpose
- interpretation of nature's order
Aristotle proposed four kinds of causes:
- material cause
- formal cause
- efficient cause
- final cause
Modern science eventually rejected final causes (purpose in nature), focusing mainly on efficient causes.
This shift marks a major philosophical transformation from teleological explanations to mechanistic explanations.