Examples include: • Thales – Proposed that water is the fundamental substance behind all existence. • Anaximander – Suggested the concept of the boundless (the apeiron) as the source of all things, exploring the origins of the cosmos. • Heraclitus – Emphasized constant change, arguing that everything is in flux and that fire is a primary element symbolizing transformation. • Parmenides – Focused on the nature of being, asserting that change is illusory and that reality is unchanging and uniform. • Empedocles – Introduced the idea of four elemental roots (earth, air, fire, water) in explaining the diversity of natural phenomena.

These thinkers moved away from mythological explanations, laying the groundwork for rational inquiry into the nature of reality.