Belief in fundamental substance

Introduced natural philosophy

Doctrine of change

Famous for "you cannot step into the same river twice"

Mathematics and mysticism

Belief in the immortality of the soul

Socratic method of inquiry

Emphasis on ethics and virtue

Theory of Forms

Writer of "The Republic"

Empirical observation and classification

Contributions to logic and metaphysics

"Cogito, ergo sum" (I think, therefore I am)

Emphasis on reason as the path to knowledge

Pantheism and determinism

Ethical implications of his philosophy

Tabula rasa concept of the mind

Foundation of modern democracy

Skepticism about causation

Inquiry into human understanding

Emphasis on individual freedom and responsibility

Concept of "existence precedes essence"

Feminist existentialism

Exploration of the "Other"

Language games and meaning

Distinction between saying and showing

Logic and philosophy of language

Contributions to analytic philosophy and social criticism

Integration of Zen Buddhism with Western thought

Promotion of Zen aesthetics and practice