philosophy

Systematic analysis and critical examination of fundamental problems such as the nature of reality, mind, perception, self, free will, causation, time and space, and moral judgements. Traditionally, philosophy has three branches: metaphysics (the nature of being), epistemology (theory of knowledge), and logic (study of valid inference). Modern philosophy also includes ethics, aesthetics, political theory, the philosophy of science, and the philosophy of religion.

In the ancient civilizations of India and China, various sages set out their views and reflections about life and ultimate reality; but philosophy as a systematic and rational endeavour originated in Greece in the 6th century BC with the Milesian school (Thales, Anaximander, Anaximenes). Both they and later pre-Socratics (Pythagoras, Xenophon, Parmenides, Zeno of Elea, Empedocles, Anaxagoras, Heraclitus, Democritus) were lively theorists, and ideas like atomism, developed by Democritus, occur in later schemes of thought.

Originally, philosophy included all intellectual endeavour, but over time traditional branches of philosophy have acquired their own status as separate areas of study. In the 5th century Socrates, foremost among the teachers known as the Sophists, laid the foundation of ethics; Plato evolved a system of universal ideas; Aristotle developed logic. Later schools include Epicureanism (Epicurus), Stoicism (Zeno) and scepticism (Pyrrho); the eclectics - not a school, they selected what appealed to them from various systems (Cicero and Seneca); and the neo-Platonists, infusing a mystic element into the system of Plato (Philo, Plotinus and, as disciple, Julian the Apostate).

The close of the Athenian schools of philosophy by Justinian AD 529 marks the end of ancient philosophy, though the Roman philosopher Boethius passed on the outlines of Greek philosophy to the West. Greek thought also survived in the work of the Arab philosophers Avicenna and Averroes, and of the Jewish philosophers Avencebrol (1021-1058) and Maimonides. In the early medieval period, Johannes Scotus Erigena formulated a neo-Platonic system. The 12th century saw the recovery of the texts of Aristotle, which stimulated the scholastic philosophers, mainly concerned with the reconciliation of ancient philosophy with Christian belief - Anselm, Abelard, Albertus Magnus, Thomas Aquinas, his opponent Duns Scotus, and William of Occam.

In the 17th century, René Descartes, Gottfried Leibniz, and Baruch Spinoza mark the beginning of modern philosophy with their rationalism and faith in mathematical proof. In the 17th and 18th centuries, the British empiricists (John Locke, George Berkeley, David Hume) turned to science and sense experience for guidance on what can be known and how. The German philosopher Immanuel Kant tried to define what we can know and to rebut both scepticism and speculative metaphysics in his critical philosophy.

In the early 19th century, classical German idealists (J G Fichte, F W J Schelling, G W F Hegel) rejected Kant's limitation on human knowledge. Notable also in the 19th century are the pessimistic atheism of Arthur Schopenhauer; the work of Friedrich Nietzsche and Søren Kierkegaard, which led towards 20th-century existentialism; the pragmatism of William James and John Dewey; and the neo-Hegelianism at the turn of the century (F H Bradley, T H Green, Josiah Royce).

Among 20th-century movements are logical positivism (Rudolf Carnap, Karl Popper, Alfred Ayer); neo-Thomism, the revival of the medieval philosophy of Aquinas (Jacques Maritain); existentialism (Martin Heidegger, Karl Jaspers, Jean-Paul Sartre); phenomenology (Edmund Husserl, Maurice Merleau-Ponty); and analytical and linguistic philosophy (Bertrand Russell, G E Moore, Ludwig Wittgenstein, Gilbert Ryle, Willard Quine). Under the influence of Russell's work on formal logic and Wittgenstein's Philosophical Investigations, English-speaking philosophers have paid great attention to the nature and limits of language, in particular in relation to the language used to formulate philosophical problems.