The pre-Socratic philosophers: Thales ; Anaximander ; Anaximenes ; Pythagoras ; Heraclitus ; Parmenides ; Zeno ; Empedocles ; Anaxagoras ; Leucippus ; Democritus -- The Athenian period: The Sophists: Protagoras ; Gorgias ; Thrasymachus ; Callicles ; Critias ; Socrates ; Plato ; Aristotle ; The Hellenestic period: Epicureanism ; Stoicism ; Neo-Platonism -- Medieval philosophy: St. Augustine ; The Encyclopediasts ; John Scotus Erigena ; St. Anselm ; The problem of faith and reason ; The problem of universals ; St. Thomas Aquinas -- The 17th and 18th centuries: Descartes ; Hobbes ; Spinoza ; Leibniz ; Locke ; Berkeley ; Hume ; Kant -- The 19th century: Hegel ; Schopenhauer ; Kierkegaard ; Marx ; Nietzsche ; Utilitarianism: Bentham ; Mill -- The 20th century: Pragmatism: James ; Dewey ; G.E. Moore ; Russell ; Logical positivism: Husserl ; Wittgenstein ; Heidegger ; Sartre ; Structuralism: Saussure ; Lévi-Strauss ; Poststructuralism: Lacan ; Derrida ; Irigaray.