Philosophy has a long history. Generally, philosophers divide the history of Western philosophy into ancient philosophy, medieval philosophy, modern philosophy, and contemporary philosophy.

Ancient Philosophy

Western Philosophy is generally said to begin in the Greek cities of western Asia Minor (Ionia) with Thales of Miletus, who was active around 585 B.C. and left us the opaque dictum, "All is water." His most noted students were Anaximenes of Miletus and Anaximander ("All is air").

Other thinkers and schools appeared throughout Greece over the next couple of centuries. Among the most important were:

Heraclitus, who stressed the transitory and chaotic nature of all things ("All is fire"; "We cannot step into the same river twice").

Anaxagoras, who conversely asserted that reality was so ordered that it must be in all respects governed by Mind.

The Pluralists and Atomists (Empedocles, Democritus) who tried to understand the world as composite of innumerable interacting parts; and the Eleatics Parmenides and Zeno who both insisted that All is One and change is impossible. Parmenides and his school emphasized the numerical, mathematical character of the world and of truth.

The Sophists, traveling professional teachers of varied philosophical affinity, became known (perhaps unjustly) for claiming that truth was no more than opinion and for teaching people to argue fallaciously to prove whatever conclusions they wished.

This whole movement gradually became more concentrated in Athens, which had become the dominant city-state in Greece.

There is considerable discussion about why Athenian culture encouraged philosophy, but one popular theory says that it occurred because Athens had a direct democracy. It's known from Plato's writings that many sophists maintained schools of debate, were respected members of society, and well paid by their students. It's also well known that orators had tremendous influence on Athenian history, possibly even causing its failure (See Battle of Miletus). The theory fills in the blanks by saying that the Sophists' students wanted to acquire the skills of an orator in order to influence the Athenian Assembly, and thereby grow wealthy and respected. Since winning debates led to wealth, the subjects and methods of debate became highly developed. Note that Western and American culture maintain this trait. Culturally, Westerners are very Greek.

The key figure in transforming Greek philosophy into a unified and continuous project - the one still being pursued today - is Socrates, who studied under several Sophists and then spent much of his life, we are told, engaging everyone in Athens in discussion trying to determine whether anyone had a very good idea what they were talking about, especially when they talked about important matters like justice, beauty and truth. He wrote nothing, but inspired many disciples. In his old age he became the focus of the hostility of many in the city who saw philosophy and sophistry, interchangeably, as destroying the piety and moral fibre of the city; he was executed in 399 B.C.

His most important student was Plato, who wrote a number of philosophical dialogues using his master's methods of inquiry to examine problems. The early dialogues demonstrate something like Socrates' own fairly inconclusive style of inquiry. The "middle" ones develop a substantive metaphysical and ethical system to resolve these problems. Central ideas are the Theory of Forms, that the mind is imbued with an innate capacity to understand and apply concepts to the world, and that these concepts are in a significant way more real, or more basically real, than the things of the world around us; the immortality of the soul, and the idea that it too is more important than the body; the idea that evil is a kind of ignorance, that only knowledge can lead to virtue, that art should be subordinate to moral purposes, and that society should be ruled by a class of philosopher kings. In the later dialogues Socrates figures less prominently, and the Theory of Forms is cast in doubt; more directly ethical questions become the focus.

Plato founded the Academy of Athens, and his most outstanding student there was Aristotle. Possibly Aristotle's most important and long-lasting work was his formalization of logic. It appears that Aristotle was the first philosopher to categorize every valid syllogism. A syllogism is a form of argument that is guaranteed to be accepted, because it is known (by all educated persons) to be valid. A crucial assumption in Aristotelian logic is that it has to be about real objects. Two of Aristotle's syllogisms are invalid to modern eyes. For example, "All A are B. All A are C. Therefore, some B are C." This syllogism fails if set A is empty.

Medieval Philosophy

Medieval philosophy was greatly concerned with the nature of God, and the application of Aristotle's logic and thought to every area of life.

If God exists at all, surely He is the most important feature of the universe, and therefore worthy of study. One continuing interest in this time was to prove the existence of God, through logic alone, if possible.

One early effort was the Cosmological Argument, conventionally attributed to Thomas Aquinas. The argument roughly, is that everything that exists has a cause. Therefore, there must be an uncaused first cause, and this is God. Aquinas also adapted this argument to prove the goodness of God. Everything has some goodness, and the cause of each thing is better than the thing caused. Therefore, the first cause is the best possible thing. Similar arguments are used to prove God's power and uniqueness.

Another important argument proof of the existence of God was the Ontological Argument. Basically, it says that God has all possible good features. Existence is good, and therefore God has it, and therefore exists.

The application of Aristotelian logic proceeded by having the student memorize a rather large set of syllogisms. The memorization proceeded from diagrams, or learning a key sentence, with the first letter of each word reminding the student of the names of the syllogisms.

Each syllogism had a name, for example "Modus Ponens" had the form of "If A is true, then B is true. A is true, therefore B is true."

Most university students of logic memorized Aristotle's 19 syllogisms of two subjects, permitting them to validly connect a subject and object. A few geniuses developed systems with three subjects, or described a way of elaborating the rules of three subjects.

As well as Aquinas, other important names from the medieval period include Duns Scotus and Peter Abelard.

Modern Philosophy

Modern philosophy generally means philosophy from 1600 until about 1900, and includes many distinguished early modern philosophers, such as Rene Descartes, John Locke, David Hume, and Immanuel Kant. Nineteenth-century philosophy is often treated as its own period, as it was dominated by post-Kantian German and idealist philosophers like Georg Hegel, Karl Marx, and F. H. Bradley; other important thinkers were John Stuart Mill, Arthur Schopenhauer and Friedrich Nietzsche.

Contemporary Philosophy

For much of the twentieth century, philosophy ran along two fairly independent - and not infrequently antagonistic - streams, roughly corresponding with whether the philosopher in question belonged to the English-speaking world - the British Isles, North America, Australasia - or continental Europe. The former approaches, which began with mathematical logic, continued through logical positivism and later linguistic philosophy and ordinary language philosophy, were broadly dubbed "analytic philosophy," interchangeably with "Anglo-American philosophy." The latter, which initially consisted mainly in phenomenology and existentialism, and later came to incorporate a great deal of Marxist and psychoanalytic social theory, literary criticism, and structuralism and post-structuralism, was dubbed "continental philosophy." By the end of the twentieth century, the two streams freely, if still not frequently, interacted, and an increasing number of professional philosophers were of the opinion that the "analytic/continental" distinction at least did not determine the "good philosophy/ bad philosophy" distinction, and arguably didn't pick out any terribly useful distinction at all.

Analytic philosophers, including Bertrand Russell, G. E. Moore, and Ludwig Wittgenstein, were centered in Oxford and Cambridge, and were joined by logical empiricists emigrating from Austria and Germany (for example, Rudolf Carnap) and their students and others in the United States (such as, W. V. Quine, Donald Davidson, and Saul Kripke, and other English-speaking countries (for example, A. J. Ayer). Gottlob Frege, a German who never worked in the English-speaking world, is arguably the foundation of this tradition, but it began with Russell and Moore in Cambridge at the turn of the century. Russell, A.N. Whitehead, and Wittgenstein (an Austrian) did groundbreaking philosophical work in math and logic. This quickly connected them with the Logical Positivists, a group of scientists and philosophers in Vienna centred around Carnap, Otto Neurath, and Moritz Schlick, and with the logical empricists in Berlin, centred around Reichenbach and Hempel, and later with a number of brilliant schools of logicians that sprang up in Poland.

During the thirties members of these various groups migrated to the United States, helping to lay the grounds for American analytic philosophy. W.V. Quine , who was influenced by all of these (particularly Carnap) is perhaps the key figure here. Also during the thirties Ludwig Wittgenstein came to doubt the philosophical tenability of the very elaborately logic-based philosophy he had earlier done, and stressed the importance of studying ordinary language and practical usage, as being crucial to untangling philosophy. His work was initially influential at Oxford, and after the posthumous publication of his many manuscripts, has spread through all of philosophy.

On the continent of Europe (especially Germany and France), the phenomenologist Germans Edmund Husserl and Martin Heidegger led the way, followed soon by Jean-Paul Sartre and other existentialists; this led via other "isms" to postmodernism, which dominates schools of critical theory as well as philosophy departments in France and Germany, which continue the projects that these philosophers have pursued.

Chronological list of important philoshophers

See also: List of philosophers for another list of philosophers.

  • Thales (620-546 BC), traditionally the first Presocratic philosopher.
  • Anaximander (610-540 BC), Ionic Presocratic, the first to write a philosophical treatise.
  • Anaximenes (fl. 6th cent. BC), Ionic Presocratic, possibly a pupil of Anaximander.
  • Heraclitus (540-480 BC), Presocratic philosopher of flux.
  • Pythagoras (570-497 BC), philosopher-mathematician based in Italy.
  • Theano (fl. 6th cent. BC), female philosopher, pupil of Pythagoras and later his wife.
  • Xenophanes (570-475 BC), Presocratic philosopher-poet pre-empting the Eleatic school.
  • Parmenides (510-440 BC), Eleatic philosopher of being.
  • Anaxagoras (500-428 BC), Presocratic, the first philosopher known to have been based in Athens.
  • Diogenes of Apollonia (fl. 5th cent. BC), Ionian Presocratic philosopher.
  • Empedocles (493-433 BC), Presocratic philosopher and cosmologist.
  • Zeno of Elea (fl. 5th cent. BC), Eleatic philosopher famous for his paradoxes of motion.
  • Leucippus (fl. 5th cent. BC), Presocratic philosopher, founder of atomism.
  • Protagoras (485-415 BC), Sophist famous for his relativism.
  • Hippias (485-415 BC), Sophist.
  • Gorgias (483-376 BC), Sophist and teacher of rhetoric.
  • Antiphon (480-411 BC), Orator and Sophist]] (if these two are in fact the same person), fragments of whose treatise On Truth were discovered at Oxyrhynchus.
  • Aspasia (fl. 5th cent. BC), female philosopher and rhetorician, companion of Socrates.
  • Socrates (469-399 BC), Athenian philosopher, put to death on charges of corrupting the youth.
  • Prodicus (fl. 5th cent. BC), Sophist contemporay with Socrates.
  • Democritus (460-370 BC), famous atomic philosopher.
  • Euclides of Megara (450-380 BC), associate of Socrates and founder of the Megarian school.
  • Antisthenes (445-360 BC), companion of Socrates, often associated with the later Cynic movement.
  • Aristippus (435-356 BC), companion of Socrates, traditionally the founder of the Cyrenaic school devoted to hedonism.
  • Plato (429-347 BC), younger associate of Socrates, founder of the Academy, teacher of Aristotle.
  • Xenophon (427-355 BC), historian and philosophical author, famous for his accounts of Socrates.
  • Speusippus (407-339 BC), pupil of Plato who succeeded him as second head of the Academy.
  • Diogenes of Sinope (400-325 BC), Cynic philosopher.
  • Xenocrates (396-314 BC), follower of Plato and third head of the Academy.
  • Aristotle (384-322 BC), pupil of Plato, founder of the Lyceum and the Peripatetic tradition.
  • Arete of Cyrene (fl. 4th cent. BC), daughter of Aristippus and his sucessor as head of the Cyrenaic school.
  • Stilpo (380-300 BC), Megarian philosopher, influenced by Cynicism and an influence on Stoicism.
  • Theophrastus (370-288 BC), pupil of Aristotle and his successor as head of the Lyceum.
  • Pyrrho (365-275 BC), founder of the scepticial philosophy named after him.
  • Epicurus (341-270 BC), atomist and hedonist philospher, founder of school named after him.
  • Zeno of Citium (335-263 BC), founder of the Stoic school.
  • Cleanthes (331-232 BC), second head of the Stoic school.
  • Aristo (fl. 3rd cent. BC), Stoic philosopher, a pupil of Zeno, focused primarily on ethics.
  • Timon (320-230 BC), sceptical philosopher, pupil of Pyrrho.
  • Arcesilaus (316-242 BC), head of Plato's Academy, perhaps responsible for its turn towards scepticism.
  • Menippus (fl. 250 BC), Cynic philosopher and famous as a satirist.
  • Chrysippus (280-207 BC), third]] (and probably most important) head of the Stoic school.
  • Diogenes of Babylon (240-152 BC), Stoic philosopher, member of the famous embassy of philosophers to Rome.
  • Carneades (214-129 BC), head of the Academy and founder of the 'New Academy', memder of the famous embassy of philosophers to Rome.
  • Panaetius (185-109 BC), Stoic philosopher with eclectic tendencies, pupil of Diogenes of Babylon and Antipater, influence upon Cicero.
  • Philo of Larissa (160-80 BC), head of the Academy, teacher of Cicero.
  • Zeno of Sidon (150-70 BC), Epicurean philosopher.
  • Posidonius (135-51 BC), Stoic philosopher and historian, often characterised as an eclectic representative of the 'Middle Stoa'.
  • Antiochus of Ascalon (130-68 BC), pupil of Philo of Larissa, head of the Academy turning it away from the scepticism of the 'New Academy' and back to the 'Old Academy'. An important influence upon Cicero.
  • Philodemus (110-40 BC), Epicurean philosopher, many of whose works were buried at Herculaneum.
  • Cicero (106-43 BC), Roman philosophical author.
  • Aenesidemus (fl. 1st cent. BC), sceptical philosopher who attempted to revive Pyrrhonism.
  • Lucretius (94-55 BC), Epicurean philosopher-poet.
  • Philo of Alexandria (30 BC - 45 AD), Jewish Hellenistic philosopher and prolific author based in Alexandria.
  • Seneca (4 BC - 65 AD), Latin Stoic author, onetime tutor to the Emperor Nero.
  • Musonius Rufus (30-100 AD), Stoic philosopher-preacher.
  • Plutarch (45-120 AD), biographer and author of an important collection of philosophical essays, the Moralia.
  • Epictetus (55-135 AD), Stoic philosopher, pupil of Musonius Rufus and founder of a school in Nicopolis.
  • Demonax (fl. 2nd cent. AD), Cynic philosopher, pupil of Epictetus.
  • Diogenes of Oenoanda (fl. 2nd cent. AD), author of Epicurean inscription at Oenoanda.
  • Alcinous (fl. 2nd cent. AD), Platonist and author of the Handbook of Platonism.
  • Marcus Aurelius (121-180 AD), Roman Emperor and Stoic philosopher.
  • Galen of Pergamum (129-199 AD), philosopher-doctor influenced by Platonism, physician to Marcus Aurelius, and prolific author.
  • Clement of Alexandria (150-215 AD), Christian Church Father heavily influenced by Greek philosophy.
  • Sextus Empiricus (fl. 200 AD), sceptical philosopher and author.
  • Alexander of Aphrodisias (fl. 200 AD), Aristotelian commentator.
  • Julia Domna (170-217 AD), female philosopher and wife of the Emperor Septimius Severus, included Galen and Philostratus in her philosophical circle.
  • Diogenes Laertius (fl. 3rd cent. AD), famous biographer of ancient philosophers.
  • Plotinus (205-270 AD), Platonic philosopher and founder of Neoplatonism.
  • Porphyry (233-309 AD), Neoplatonist, pupil and biographer of Plotinus.
  • Iamblichus (242-327 AD), important Neoplatonic philosopher.
  • Calcidius (fl. 4th cent. AD), Platonist and author of an important Latin translation and commentary on the Timaeus.
  • Themistius (317-388 AD), Aristotelian commentator based in Constantinople.
  • Augustine of Hippo (354-430 AD), Christian philosopher and Church father, influenced by Neoplatonism.
  • Hypatia (370-415 AD), famous female Neoplatonist based Alexandria and murdered by a Christian mob.
  • Proclus (411-485 AD), Athenian Neoplatonist and head of the Academy.
  • Ammonius (440-521 AD), Alexandrian Neoplatonist, a pupil of Proclus and teacher of Damascius and Simplicius.
  • Damascius (462-540 AD), Neoplatonist and head of the Athenian school.
  • Boethius (475-524 AD), Latin Neoplatonist and translator of Aristotle.
  • Simplicius (490-560 AD), Aristotelian commentator, pupil of Damascius.
  • John Philoponus (490-570 AD), Christian Aristotelian commentator based in Alexandria, pupil of Ammonius.
  • John Scotus Erigena (810-877 AD) Also called "John the Scot".
  • Anselm (11th century) Posed the ontological argument for the existence of God.
  • Peter Abelard (1079-1142 AD) Aristotelian (nominalist) lived a great love story similar to Romeo and Juliet.
  • Roger Bacon (1220-1292 AD) He believed there could and should be a unified science based on observation, experiment and abstract reasoning.
  • Thomas Aquinas (1224-1274 AD) Tried to merge the already Platonized Christianity with the philoshophy of Aristotle maintaining a distinction between philoshophy and religion.
  • Duns Scotus (1266-1308 AD) Heavily criticized Aquinas.
  • William of Ockham (1285-1347 AD) Observation nature and reason can only provide us with reliable knowledge about the world, famous for his principle of accepting the simplest of alternatives as the best one (Ockham's Razor).
  • Copernicus (1473-1543 AD) Polish churchman who hypothesized that many mathematical difficulties of the time would disappear if we assumed sun was at the center of our planetary system instead of earth (and flatly contradicting the Bible).
  • Niccolo Machiavelli (1469-1527 AD) Studied politics and government in an objective (scientific) manner.
  • Tycho Brahe (1546-1601 AD) Astronomer with vast body of measured astronomical observations passed on the Johannes Kepler.
  • Francis Bacon (1561-1626 AD) Believed that scientific knowledge could give power of man over nature. He also believed the idea that definitions advance knowledge was an illusion (Aristotle's idea?).
  • Galileo Galilei (1564-1642 AD) Believed to be founding father of modern science with study of projectiles, pendulum, gravity. Discovered the thermometer. Asserted that earth revolves around its axis.
  • Johannes Kepler (1571-1630 AD) Studied theology but he showed that planets move in elliptical motion around the sun (not circular as previously thought by Copernicus).
  • Thomas Hobbes (1588-1679 AD) Believed that only matter existed, everything could be explained in terms of matter in motion. The whole universe he considered a giant machine. In politics he claimed its the fear of death that forces humans to form societes, and proposed that everyone should agree to hand power to a central authority whose job is to impose law and punish lawbreakers (police state).
  • Rene Descartes (1596-1650 AD) Invented analytic geometry, the graph, looked at humans contradicted themselves and wondered whether there was something that we could know for certain. Famous for his "I think therefore I am".
  • Benedict Spinoza (1632-1677 AD) He believed that our physical body and the soul is one entity. He believed that for the most part we are not aware of the real causes of our actions. Being deprived of freedom of speech himself he was from the first to proclaim its importance.
  • Isaac Newton (1642-1727 AD) Accuratelly analyzed the constituents of light, invented calculus, formulated the gravitational theory, and provided us with accurate account of movements of planets through space.
  • Gottfried Leibniz (1646-1716 AD) Invented calculus independently of Newton, was offered professorship at 21 which he turned down. Claimed that truths belong in two categories the ones that can be verified with just examining them with logical statements and the ones that need further observation and application of logic.