- systematic inquiry into fundamental questions: existence, knowledge, truth, value, reason, mind, language
- branches: metaphysics (what exists), epistemology (what can be known), ethics (what is right), logic (valid reasoning), aesthetics (beauty and art)
- originated independently in Greece, India, and China during the Iron Age Axial Age (~800-200 BCE)
- Greek tradition: Socrates, Plato, Aristotle → foundation of Western science and logic
- Indian tradition: Vedanta, Buddhism, Jainism → analysis of consciousness, suffering, liberation
- Chinese tradition: Confucianism, Daoism, Legalism → social harmony, governance, natural order
- Islamic Golden Age preserved and extended Greek philosophy (Al-Kindi, Avicenna, Averroes)
- modern branches: philosophy of mind, philosophy of language, philosophy of science
- cyber embeds an epistemology: knowledge is what agents link, rank, and verify through consensus