Pre-Socratic Philosophy
The first Western philosophers (6th-5th century BCE). They asked: what is everything made of? Thales said water, Heraclitus said fire and flux, Parmenides said change is illusion, Democritus said atoms.
Sub-topics
Heraclitus of Ephesus (~535-475 BCE). 'Everything flows' (panta rhei). Reality is constant change governed by the Logos. You cannot step into the same river twice. Unity of opposites.
Parmenides of Elea (~515-450 BCE). Being is one, unchanging, and eternal. Change and motion are illusions. His rigorous deductive method influenced all subsequent metaphysics.
Democritus of Abdera (~460-370 BCE). Co-founder of atomism with Leucippus. Reality is atoms and void. All qualities emerge from the arrangement of indivisible particles — anticipating modern physics by 2400 years.