1: Pre-Socratic natural philosophy

Pre-Socratic Natural Philosophy

Long before modern labs and textbooks, thinkers in ancient Greece (6th–5th centuries BCE) asked revolutionary questions about nature. Known as the Pre-Socratics, they rejected mythological explanations for natural phenomena. Instead, they pioneered rational inquiry—seeking universal principles ($archê$) governing the cosmos ($kosmos$). Their work laid the groundwork for science and philosophy by insisting nature follows consistent, observable laws.

Key Questions and Methods

Pre-Socratics focused on fundamental puzzles:

• What is the universe made of?
• How does change occur?
• Can reality be reduced to a single substance?

They observed everyday elements—water, air, fire—and debated patterns in weather, celestial movements, and life cycles. Unlike poets who invoked gods, they used logic and analogy. For example, noting how water turns to vapor or ice, they theorized about transformation in all matter.

Major Figures and Theories

• Thales of Miletus (c. 624–545 BCE): Proposed water as the primal element. He observed water’s role in fertility, weather, and geography, suggesting it underpinned all existence.
• Anaximander (Thales’ student): Argued the source of everything was $apeiron$ (the boundless)—an infinite, undefined substance. He also sketched early evolutionary ideas, claiming humans evolved from fish-like creatures.
• Heraclitus (c. 535–475 BCE): Famous for declaring $panta rhei$. He saw fire as the fundamental element, symbolizing constant change: "You cannot step into the same river twice."
• Parmenides (c. 515–450 BCE): Contradicted Heraclitus, arguing change is an illusion. True reality, he claimed, is eternal, unchanging, and indivisible—a concept challenging sensory experience.
• Empedocles (c. 494–434 BCE): Bridged ideas, proposing four roots (earth, air, fire, water) mixed and separated by cosmic forces: Love (attraction) and Strife (repulsion).
• Democritus (c. 460–370 BCE): Developed atomism, asserting all matter comprises invisible, indivisible particles ($atomos$) moving in void space—a startlingly modern insight.

Legacy

These thinkers sparked debates about unity vs. plurality, permanence vs. change, and observation vs. reason. Their emphasis on natural—not supernatural—causes shifted human thought toward systematic investigation. Though their speculations weren’t always testable, their insistence on rational inquiry paved the way for Aristotle’s biology, Euclid’s geometry, and later scientific revolutions.