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).
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.
| c. 2500 BC | Egypt | Ptahhotep, governor of Memphis at the time of the 5th dynasty of Egypt, writes the first known book of philosophy, his Instructions to his son. |
| 705 BC | Greece | The poet and farmer Hesiod of Boeotia, Greece, writes his Works and Days, a compilation of practical and ethical advice based on rural life, which is also the first recorded instructional book on agricultural practice, and his Theogony, which gives an account of the origin of the world and the birth of the Greek gods. He and Homer are said to have ‘given the Greeks their gods’. |
| 570 BC | Greece | Greek astronomer and philosopher Anaximander of Miletus continues the work of the Greek philosopher Thales of Miletus and his speculation on ultimate reality, in On the Nature of Things. |
| 540 BC | Greece | Greek astronomer and philosopher Anaximenes of Miletus, who studies cosmogony, the study of the origins of the universe, is active. |
| 517 BC | China, Zhou Kingdom | Chinese philosophers Confucius and Lao Zi (Lao Tzu) reputedly meet. Lao Zi, who is credited with Tao Te Ching/The Book of the World Law and its Power, may be a mythical founder figure, invented to support the philosophy of Taoism. |
| c. 500 BC | Greece | Greek philosopher Heraclitus of Ephesus centres his philosophy on the proposition that ‘everything flows’, and the belief that the cosmos is in a constant process of change. |
| c. 470 BC | China | The disciples of the Chinese philosopher Confucius reputedly collect and record his teachings, which are ethical rather than religious and centre on the golden rule of doing to others as one would have done to oneself. |
| c. 445 BC | Greece | Greek philosopher and scientist Empedocles distinguishes the ‘four elements’ – earth, fire, water, and air – which he claims all substances are made of, and which also explain the development of the universe by the forces of attraction and repulsion. The doctrine is embodied in Aristotle's works and influences Western thought until the 17th century AD. |
| c. 430 BC | Greece | Athenian philosopher Socrates is active. He claims to know nothing and to be a ‘midwife to truth’, bringing forth the truth which others already know, but his participation in intellectual debates changes philosophy, focusing it on the inner nature of humanity. He writes no accounts of his work and, in later times, is known mainly through the works of the philosophers and historians Plato, Xenophon, and Aristotle. |
| 399 BC | Greece | Athenian philosopher Socrates is convicted for impiety and for corrupting the young. He is sentenced to death by drinking the poison hemlock, but is also offered the option of exile which, despite entreaties from his friends, he refuses. His last days are described by his pupil, the philosopher Plato, in Apology and Phaedo. |
| c. 380 BC | Greece | The Greek philosopher Plato reputedly composes his first group of Socratic dialogues, including Ion, Laches, Lysis, Apology, Euthyphro, Charmides, Menexenus, Hippias Major, Hippias Minor, Protagoras, Crito, and Cleitophon. |
| 330 BC–323 BC | Greece | Greek philosopher Aristotle composes his History of Animals, Rhetoric, Physics, Metaphysics, Nicomachean Ethics, Logic, Poetics, Politics, and a large number of other works. In politics he shows no sympathy with either his one-time pupil Alexander the Great, King of Macedon, or the democracy of Athens. |
| c. 300 BC | Greece | Greek philosopher Zeno of Citium, having lived and studied in Athens for about 12 years, opens his Stoic school of philosophy at the Stoa Poikile there, which specializes in paradoxes. Legend tells that Zeno lives to the age of 98. |
| 55 BC | Rome, Asia Minor | Roman orator and writer Marcus Tullius Cicero wishes to retire from public life to concentrate on literary pursuits, publishing his De oratore/The Orator this year and finishing De republica/On the Republic in the following year. However, in 51 BC he is appointed governor of Cilicia, in Asia Minor, and goes reluctantly. |
| c. 37 | Roman Empire | The Latin writer and statesman Lucius Annaeus Seneca begins work on a series of essays expounding Stoic philosophy. Among the better known are ‘De otio’/‘On Leisure’ and ‘Ad Marciam de consolatione’/‘The Consolation of Marcia’. |
| 174 | Roman Empire | While on various military campaigns, Roman emperor Marcus Aurelius composes his Meditations: philosophical thoughts, influenced by Stoicism, which reflect his disillusionment with the aspirations of mankind and his own sense of duty. |
| c. 799 | India | Shankara, the Brahman philosopher and theologian, is active in this period. An exponent of the Advaita Vedanta school, he writes commentaries on the Upanishads, Hindu philosophical writings, which affirm his belief in an everlasting and unchanging reality. |
| c. 1122 | France | The theologian and philosopher Peter Abelard writes his Sic et non/Yes and No, a collection of seemingly contradictory statements from the Bible and the Christian Fathers, compiled in order to promote rational discussion. |
| 1142 | France | The philosopher and theologian Peter Abelard writes his ‘Letters’ to his former lover Héloïse, including the celebrated autobiography Historia calamitatum mearum/Story of My Misfortunes. |
| 1191 | Spain, Egypt | Jewish philosopher Moses Maimonides completes his major work, Dalalat al-Ha'irin/A Guide for the Perplexed, an attempt at a rational philosophy of Judaism aimed at reconciling Jewish theology and Muslim Aristotelianism. |
| 1327 | France | French-born Jewish philosopher Levi ben Gerson (Gersonides) completes his Milhamot Adonai/Wars of the Lord, a philosophical defence of Judaism based on Aristotle. |
| c. 1440 | Italy | Italian scholar and humanist Lorenzo Valla publishes his treatise De libero arbitrio/On Free Will. |
| 1440 | Germany | German churchman and philosopher Nicholas of Cusa (Nicolaus Cusanus) publishes De docta ignorantia/On Learned Ignorance. |
| 1480 | Netherlands | Dutch humanist scholar and poet Rudolph Agricola (Roelof Huysman) publishes De inventione dialectica/On Dialectic Invention, a defence of Renaissance humanism. Agricola's works make a deep impression on Desiderius Erasmus. |
| 1509 | England | Dutch humanist Desiderius Erasmus makes his third and longest visit to England (staying until 1514) and lectures at Cambridge. Living much of the time with the English statesman and scholar Thomas More, he writes Encomium moriae/In Praise of Folly, which is published in 1511. |
| 1521 | Italy | Italian political writer Niccolò Machiavelli publishes Dell'arte della guerra/On the Art of War. It is translated into English in 1560 as Seven Books on the Art of War. |
| 1558 | Swiss Confederation | Scottish religious leader John Knox publishes The First Blast of the Trumpet Against the Monstrous Regiment of Women in Geneva, Swiss Confederation. It is an attack on Mary of Guise (Mary of Lorraine). |
| 1571 | Italy | The Italian physician and botanist Andrea Cesalpino publishes Quaestionum peripateticarum/Peripatetic Investigations in Venice, Italy, a work of Aristotelian natural philosophy. |
| 1584 | Italy | Italian philosopher Giordano Bruno publishes La cena de le Ceneri/The Ash Wednesday Supper, in which he argues in favour of the Copernican system, De l'infinito universo e mondi/On the Infinite Universe and Worlds, the central statement of his belief in an infinite universe animated by a ‘world soul’, and Spaccio della bestia trionffante/Banishment of the Triumphant Beast, an ethical treatise dedicated to the English poet Philip Sidney. |
| 1597 | England | English statesman and writer Francis Bacon, Lord Verulam, publishes Essays: Civil and Moral, his first book of essays. A second, enlarged edition appears in 1612. |
| 1623 | Italy | Italian philosopher Tommaso di Campanella publishes La città del sole/The City of the Sun, which describes his conception of utopia. |
| 1630 | Bohemia | Bohemian philosopher and educational reformer Comenius publishes Labyrint Sveta a ráj srdce/The Labyrinth of the World and the Paradise of the Heart, his most important philosophical work. |
| 1637 | France | French philosopher and mathematician René Descartes publishes Discours de la méthode/Discourse on Method. A radical approach to the theory of knowledge, it marks the beginning of modern philosophy. It contains the well-known statement: ‘Je pense, donc je suis’ (‘I think, therefore I am’). |
| 1641 | France | French philosopher René Descartes publishes Meditationes de Prima Philosophia/Meditations of the First Philosophy, in Latin. The French version follows in 1647. In this major philosophical work – one of the key works of modern philosophy – Descartes attempts to demonstrate the existence of God, the possibility of knowledge, and his famous distinction between mind and body. |
| 1644 | France | French philosopher René Descartes publishes Principia philosophiae/Principles of Philosophy in Latin (a French version follows in 1647). This work brings together his philosophy and his scientific theories. |
| 1647 | France | The French philosopher René Descartes publishes Méditations Métaphysiques/Metaphysical Meditations, the French translation of his Meditationes de Prima Philosophia/Meditations of the First Philosophy, originally published in 1641. He also publishes Principes de la philosophie/Principles of Philosophy, a French version of his Principia philosophiae, originally published in 1644. |
| 1710 | Ireland | The Irish philosopher George Berkeley publishes a treatise concerning sense perceptions, suggesting all knowledge is acquired by direct experience – the foundation of scientific empiricism. |
| 1739 | Scotland | Scottish philosopher David Hume publishes the first volume of his three-volume A Treatise of Human Nature. The work is completed in 1740. A major work of modern philosophy, it plays a central role in the tradition of British empiricism. Largely ignored at the time, it is reworked as his Enquiry Concerning Human Understanding in 1751. |
| 1770 | France | The French philosopher Baron d'Holbach (Paul Heinrich Dietrich) publishes Système de la nature/System of Nature under the name J B Mirabaud. Its outspoken attack on Christianity provokes critical responses from Voltaire and Frederick the Great. |
| 1781 | Germany | The German philosopher Immanuel Kant publishes the first of his major works, the Critique of Pure Reason, which explores the theory of knowledge. It will become one of the central works of modern philosophy. |
| 1788 | Germany | The German philosopher Immanuel Kant publishes the second of his major works, Kritik der practischen Vernunft/Critique of Practical Reason, which deals with ethics. |
| 1790 | Germany | The German philosopher Immanuel Kant publishes the third of his three major works, Critique of Judgment, which deals with aesthetics. |
| 1793 | Germany | The German philosopher Immanuel Kant publishes Die Religion innerhalb der Grenzen des blossen Vernunft/Religion within the Boundaries of Reason, in which he argues that although belief in God cannot be established by reason, it is acceptably based on ‘practical reason’. |
| 1807 | Germany | The German philosopher Georg Wilhelm Friedrich Hegel publishes Phänomenologie des Geistes/Phenomenology of Spirit. His first major work, it gives a sketch of his elaborate metaphysical system. |
| 1808 | Germany | The German philosopher Johann Gottlieb Fichte publishes Reden an die deutsche Nation/Addresses to the German Nation. This work plays an important role in the development of German nationalism. |
| 1812 | Germany | The German philosopher Georg Wilhelm Friedrich Hegel publishes the first part of his Wissenschaft der Logic/The Science of Logic. In this work he sets out his famous three-part ‘dialectic’ of thesis, antithesis, and synthesis. The second part appears in 1816. |
| 1819 | Germany | The German philosopher Arthur Schopenhauer publishes Die Welt als Wille und Vorstellung/The World as Will and Idea. His major work, it has a profound influence on German culture. |
| 1830 | France | The French sociologist Auguste Comte publishes the first part of his Cours de philosophie positive/Course of Positive Philosophy. The final part appears in 1842. |
| 1836 | USA | The US Unitarian minister, philosopher, and poet Ralph Waldo Emerson publishes his essay ‘Nature’, one of the central works of the US literary and philosophical movement Transcendentalism. |
| 1836 | Germany | The German philosopher Arthur Schopenhauer publishes Über den Willen in der Natur/On the Will in Nature. |
| 1843 | England | The English philosopher John Stuart Mill publishes The System of Logic. |
| 1843 | Denmark | The Danish philosopher Søren Aabye Kierkegaard publishes Enten-Eller/Either/Or, his first major philosophical work, and Frygt og baeven/Fear and Trembling. His analysis of choice makes this work one of the early classics of existentialism. |
| 1848 | Germany | The German political philosophers Karl Marx and Friedrich Engels publish Manifest der Kommunistischen Partei/Manifesto of the Communist Party, one of the central works of Marxism. It contains the famous lines: ‘Workers of the world unite. You have nothing to lose but your chains.’ |
| 1862 | England | The English philosopher John Stuart Mill publishes Utilitarianism, an influential work on moral philosophy. |
| 1883 | Germany | The German philosopher Friedrich Nietzsche publishes the first part of his Also sprach Zarathustra/Thus Spake Zarathustra. The final part appears in 1885. It is in this work that he develops his concept of the übermensch (superman). |
| 1892 | USA | The US philosopher William James publishes The Will to Believe and Other Essays in Popular Philosophy. |
| 1893 | UK | The British philosopher Francis Herbert Bradley publishes Appearance and Reality. |
| 1896 | France | The French philosopher Henri Bergson publishes Matière et Mémoire/Matter and Memory. |
| 1901 | | German philosopher Edmund Husserl publishes Logische Untersuchungen/Logical Investigations. |
| 1902 | | The Italian philosopher Benedetto Croce publishes Estetica come scienza dell'espressione e linguistica generale/Aesthetics as the Science of Expression and General Linguistics. |
| 1902 | | US philosopher William James publishes Varieties of Religious Experience: Two Supposed Objections to the Doctrine. |
| 1903 | | English philosopher G E Moore publishes his influential study of ethics Principia Ethica/Principles of Ethics. |
| 1905 | | Spanish-born US philosopher and writer George Santayana publishes The Life of Reason. |
| 1907 | | French philosopher Henri Bergson publishes L'Evolution créatrice/Creative Evolution. |
| 1907 | | US philosopher William James publishes Pragmatism: A New Way for Some Old Ways of Thinking. |
| 1908 | | French social philosopher Georges Sorel publishes Réflexions sur la violence/Reflections on Violence. |
| 1909 | | Italian philosopher Benedetto Croce publishes Logica come scienza del concetto puro/Logic as the Science of Pure Concept. |
| 1909 | | US philosopher William James publishes The Meaning of Truth: A Sequel to ‘Pragmatism’. |
| 1917 | | Italian philosopher Benedetto Croce publishes Teoria e storia della storiografia/History: Its Theory and Practice. |
| 1920 | | English philosopher Alfred North Whitehead publishes The Concept of Nature. |
| 1922 | | US philosopher John Dewey publishes Human Nature and Conduct. |
| 1922 | | Austrian philosopher Ludwig Wittgenstein publishes Tractatus Logico-Philosophicus/Tract on Logic and Philosophy, a classic of 20th-century philosophy that analyses the relationship between language and reality. |
| 1923 | | Hungarian cultural philosopher György Lukács publishes Geschichte und Klassenbewusstein: Studien über marxistische Dialektik/History and Class Consciousness: Studies in Marxist Dialectic. |
| 1923 | | Chance, Love, and Logic: Philosophical Essays by the Late Charles S Pierce is published posthumously, edited by the US philosopher Morris R Cohen. Though one of the most important US philosophers of the 19th century, Pierce published very little during his lifetime. |
| 1927 | | German philosopher Martin Heidegger publishes his central work Sein und Zeit/Being and Time. |
| 1928 | | German philosopher Rudolf Carnap publishes Der logische Aufbau der Welt/The Logical Structure of the World and Scheinproblem in der Philosophie/Pseudo-Problems in Philosophy. |
| 1929 | | Spanish philosopher José Ortega y Gasset publishes La rebelión de las masas/The Revolt of the Masses. |
| 1930 | | German philosopher Moritz Schlick publishes Fragen der Ethik/Problems of Ethics. |
| 1931 | | US philosopher John Dewey publishes Philosophy and Civilization. |
| 1932 | | German philosopher Karl Jaspers publishes his three-volume Philosophie/Philosophy, in which he expounds his own distinctive form of existentialism. |
| 1934 | | Austrian-born English philosopher Karl Popper publishes Logik der Forschung/The Logic of Scientific Discovery. |
| 1936 | England | The English philosopher A J Ayer publishes Language, Truth, and Logic. A brilliant exposition of logical positivism, its claim that the statements of morality and religion are, literally, ‘meaningless’, makes it the most controversial British philosophical work of the period. |
| 1941 | France | The French philosopher Etienne Gilson publishes God and Philosophy, lectures delivered at Yale University in New Haven, Connecticut. |
| 1942 | USA | The US philosopher Susanne Langer publishes Philosophy in a New Key. |
| 1943 | France | The French writer and philosopher Jean-Paul Sartre publishes L'Etre et le néant/Being and Nothingness. His most important philosophical work, it becomes a central text of the philosophy of existentialism. |
| 1944 | USA | The US social philosopher Lewis Mumford publishes The Condition of Man. |
| 1945 | France | The French philosopher Maurice Merleau-Ponty publishes Phénoménologie de la perception/Phenomenology of Perception. |
| 1946 | England | The Idea of History by the English philosopher R G Collingwood is published posthumously. |
| 1947 | Germany | The German philosophers Theodor Adorno and Max Horkheimer publish Dialektik der Aufklärung/Dialectic of Enlightenment. |
| 1947 | Italy | Lettere del carcere/Prison Notebooks by the Italian political thinker Antonio Gramsci is published posthumously. |
| 1947 | France | La Pesanteur et la grâce/Gravity and Grace by the French philosopher and mystic Simone Weil is published posthumously. |
| 1949 | France | L'Enracinement/The Need for Roots by the French philosopher and mystic Simone Weil is published posthumously. |
| 1949 | England | The English philosopher Gilbert Ryle publishes The Concept of Mind. |
| 1951 | USA | US philosopher Nelson Goodman publishes The Structure of Appearance. |
| 1953 | USA | US philosopher Willard V Quine publishes From a Logical Point of View: Nine Logico-Philosophical Essays. |
| 1953 | Austria | Philosophical Investigations by the Austrian philosopher Ludwig Wittgenstein is published posthumously. This work (which marks a complete break with his early philosophy) has a profound impact on Anglo-American philosophy. |
| 1953 | Germany | German philosopher Martin Heidegger publishes Einführung in die Metaphysik/An Introduction to Metaphysics. |
| 1955 | USA | US political journalist Walter Lippmann publishes The Public Philosophy. |
| 1956 | USA | Polish-born US philosopher Alfred Tarski publishes Logic, Semantics, and Metamathematics. |
| 1958 | USA | The German-born US philosopher Hannah Arendt publishes The Human Condition. |
| 1958 | Austria | The notebooks, The Blue Book and The Brown Book, of the Austrian philosopher Ludwig Wittgenstein are published posthumously. |
| 1958 | Germany | The German physicist and philosopher Werner Heisenberg publishes Physics and Philosophy. |
| 1958 | England | The Russian-born English philosopher Isaiah Berlin publishes Two Concepts of Liberty. |
| 1959 | England | The English philosopher P F Strawson publishes Individuals: An Essay in Descriptive Metaphysics. |
| 1962 | Japan | Japanese philosopher D T Suzuki publishes The Essentials of Zen Buddhism. |
| 1962 | Germany | German philosopher Martin Heidegger publishes Die Technik und die Kehre/The Question Concerning Technology. |
| 1963 | Germany | The German philosopher Jürgen Habermas publishes Theorie und Praxis/Theory and Practice. |
| 1969 | France | The French philosopher Michel Foucault publishes L'Archéologie de savoir/The Archaeology of Knowledge. |
| 1969 | England | Russian-born English philosopher Isaiah Berlin publishes Four Essays on Liberty. |
| 1970 | USA | The US philosopher W V Quine publishes his Philosophy of Logic and The Web of Belief. |
| 1974 | France | French philosopher Louis Althusser publishes Eléments d'autocritique/Essays in Self-Criticism. |
| 1977 | France | French historian Philippe Ariès publishes The Hour of Our Death. |
| 1981 | England | English philosopher R M Hare publishes Moral Thinking. |
| 1982 | USA | US philosopher Richard Rorty publishes The Consequences of Pragmatism. |