Major World Philosophers

General Information

Abelard, Peter
(1079 - 1142). French philosopher. One of the most influential medieval logicians and theologians. Around 1113, while teaching theology in Paris, Abelard fell in love with his student Heloise, whom he secretly married; he was condemned for heresy a few years later because of his nominalist views about universals.
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(c. 500 - 428 B.C.). Greek Presocratic philosopher who is said to have made Athens the center of philosophy and to have been Socrates' teacher; he rejected the four elements theory of Empedocles and posited instead an infinite number of unique particles of which all objects are composed.
Anselm, St.
(1033 - 1109). Italian monk and Scholastic theologian who became archbishop of Canterbury. St. Anselm founded Scholasticism, integrated Aristotelian logic into theology, and believed that reason and revelation are compatible. He is most famous for his influential ontological argument for God's existence.
Aquinas, St. Thomas
(1225 - 74). The greatest thinker of the Scholastic School. His ideas were, in 1879, made the official Catholic philosophy. He incorporated Greek ideas into Christianity by showing Aristotle's thought to be compatible with church doctrine. In his system, reason and faith (revelation) form two separate but harmonious realms whose truths complement rather than oppose one another. He presented influential philosophical proofs for the existence of God.
(384 - 322 B.C.). Greek philosopher, scientist, logician, and student of many disciplines. Aristotle studied under Plato and became the tutor of Alexander the Great. In 335 he opened the Lyceum, a major philosophical and scientific school in Athens. Aristotle emphasized the observation of nature and analyzed all things in terms of "the four causes." In ethics, he stressed that virtue is a mean between extremes and that man's highest goal should be the use of his intellect. Most of Aristotle's works were lost to Christian civilization from the fifth through the twelfth centuries.
Augustine of Hippo, St.
(354 - 430). The greatest of the Latin church fathers and possibly the most influential Christian thinker after St. Paul. St. Augustine emphasized man's need for grace. His Confessions and The City of God were highly influential.
(1126 - 98). Spanish-born Arabian philosopher, lawyer, and physician whose detailed commentaries on Aristotle were influential for over 300 years. He emphasized the compatibility of faith and reason but believed philosophical knowledge to be derived from reason. The Church condemned his views.
(980 - 1037). Islamic medieval philosopher born in Persia. His Neoplatonist interpretation of Aristotle greatly influenced medieval philosophers, including St. Thomas Aquinas. Avicenna was also a physician; his writings on medicine were important for nearly 500 years.
Bacon, Sir Francis
(1561 - 1626). English statesman, essayist, and philosopher, one of the great precursors of the tradition of British empiricism and of belief in the importance of scientific method. He emphasized the use of inductive reasoning in the pursuit of knowledge.
(c. 475 - 535). Roman statesman, philosopher, and translator of Aristotle, whose Consolation of Philosophy (written in prison) was widely read throughout the Middle Ages; it showed reason's role in the face of misfortune and was the link between the ancient philosophers and the Scholastics.
Descartes, Rene
(1596 - 1650). French philosopher and scientist, considered the father of modern philosophical inquiry. Descartes tried to extend mathematical method to all knowledge in his search for certainty. Discarding the medieval appeal to authority, he began with "universal doubt," finding that the only thing that could not be doubted was his own thinking. The result was his famous "Cogito, ergo sum," or "I think, therefore I am."
Dewey, John
(1859 - 1952). Leading American philosopher, psychologist, and educational theorist. Dewey developed the views of Charles S. Peirce (1839 - 1914) and William James into his own version of pragmatism. He emphasized the importance of inquiry in gaining knowledge and attacked the view that knowledge is passive.
Hegel, Georg Wilhelm Friedrich
(1770 - 1831). German philosopher whose idealistic system of metaphysics was highly influential; it was based on a concept of the world as a single organism developing by its own inner logic through trios of stages called "thesis, antithesis, and synthesis" and gradually coming to embody reason. Hegel held the monarchy to be the highest development of the state.
Heidegger, Martin
(1889 - 1976). German philosopher who studied with Husserl. Heidegger's own philosophy, which was influenced by Kierkegaard, emphasized the need to understand "being," especially the unique ways that humans act in and relate to the world.
Hobbes, Thomas
(1588 - 1679). English materialist and empiricist, one of the founders of modern political philosophy. In the Leviathan, Hobbes argued that because men are selfish by nature, a powerful absolute ruler is necessary. In a "social contract," men agree to give up many personal liberties and accept such rule.
Hume, David
(1711 - 76). British empiricist whose arguments against the proofs for God's existence are still influential. Hume held that moral beliefs have no basis in reason, but are based solely on custom.
James, William
(1842 - 1910). American philosopher and psychologist, one of the founders of Pragmatism, and one of the most influential thinkers of his era. James viewed consciousness as actively shaping reality, defined truth as "the expedient" way of thinking, and held that ideas are tools for guiding our future actions rather than reproductions of our past experiences.
Kant, Immanuel
(1724 - 1804). German philosopher, possibly the most influential of modern times. He synthesized Leibniz's rationalism and Hume's skepticism into his "critical philosophy": that ideas do not conform to the external world, but rather the world can be known only insofar as it conforms to the mind's own structure. Kant claimed that morality requires a belief in God, freedom, and immortality, although these can be proved neither scientifically nor by metaphysics.
Kierkegaard, Soren
(1813 - 55). Danish philosopher, religious thinker, and extraordinarily influential founder of existentialism. Kierkegaard held that "truth is subjectivity," that religion is an individual matter, and that man's relationship to God requires suffering.
Leibniz, Gottfried Wilhelm
(1646 - 1716). German philosopher, diplomat, and mathematician, one of the great minds of all time. Leibniz was an inventor (with Sir Isaac Newton) of the calculus and a forefather of modern mathematical logic. He held that the entire universe is one large system expressing God's plan.
Locke, John
(1632 - 1704). Highly influential founder of British empiricism. Locke believed that all ideas come to mind from experience and that none are innate. He also held that authority derives solely from the consent of the governed, a view that deeply influenced the American Revolution and the writing of the U.S. Constitution.
Machiavelli, Niccolo
(1469 - 1527). Italian Renaissance statesman and political writer. In The Prince, one of the most influential political books of modern times, Machiavelli argues that any act of a ruler designed to gain and hold power is permissible. The term Machiavellian is used to refer to any political tactics that are cunning and power-oriented.
(1135 - 1204). Spanish-born medieval Jewish philosopher and thinker. Maimonides tried to synthesize Aristotelian and Judaic thought. His works had enormous influence on Jewish and Christian thought.
Marx, Karl
(1818 - 83). German revolutionary thinker, social philosopher, and economist. His ideas, formulated with Engels, laid the foundation for nineteenth-century socialism and twentieth-century communism. Although Marx was initially influenced by Hegel, he soon rejected Hegel's idealism in favor of materialism. His Communist Manifesto and Das Kapital are among the most important writings of the last 200 years.
Mill, John Stuart
(1806 - 73). English empiricist philosopher, logician, economist, and social reformer. His System of Logic described the basic rules for all scientific reasoning. As a student of Jeremy Bentham, he elaborated on utilitarian ethics; in On Liberty, he presented a plea for the sanctity of individual rights against the power of any government.
Moore, G. E. (George Edward)
(1873 - 1958). British philosopher who emphasized the "common sense" view of the reality of material objects. In ethics, Moore held that goodness is a quality known directly by moral intuition and that it is a fallacy to try to define it in terms of anything else.
More, Sir Thomas
(1478 - 1535). A leading Renaissance humanist and statesman, Lord Chancellor of England. More was beheaded for refusing to accept the king as head of the Church. Influenced by Greek thinking, he believed in social reform and drew a picture of an ideal peaceful state in his Utopia.
Nietzsche, Friedrich Wilhelm
(1844 - 1900). German philosopher, philologist, and poet. As a moralist, he rejected Christian values and championed a "Superman" who would create a new, life-affirming, heroic ethic by his "will to power."
Pascal, Blaise
(1623 - 62). French philosopher, mathematician, scientist, and theologian. His posthumous Pensees ("Thoughts") argues that reason is by itself inadequate for man's spiritual needs and cannot bring man to God, who can be known only through mystic understanding.
(c. 428 - c. 348 B.C.). Athenian father of Western philosophy and student of Socrates, after whose death he traveled widely. On returning to Athens, he founded an Academy, where he taught until he died. His writings are in the form of dialogues between Socrates and other Athenians. Many of Plato's views are set forth in The Republic, where an ideal state postulates philosopher kings, specially trained at the highest levels of moral and mathematical knowledge. Plato's other works analyzed moral virtues, the nature of knowledge, and the immortality of the soul. His views on cosmology strongly influenced the next two thousand years of scientific thinking.
(205 - 270). Egyptian-born founder of Neoplatonism, who synthesized the ideas of Plato and other Greek philosophers. Plotinus believed all reality is caused by a series of outpourings (called emanations) from the divine source. Although not himself a Christian, he was a major influence on Christianity.
Rousseau, Jean Jacques
(1712 - 78). Swiss-French thinker, born in Geneva. Rousseau has been enormously influential in political philosophy, educational theory, and the Romantic movement. In The Social Contract (1762), he viewed governments as being expressions of the people's "general will," or rational men's choice for the common good. Rousseau emphasized man's natural goodness.
Russell, Bertrand
(1872 - 1970). English philosopher and logician influential as an agnostic and a pacifist. Early work with Alfred North Whitehead gave birth to modern logic. Russell changed his views numerous times but always sought to establish philosophy, especially epistemology, as a science.
Santayana, George
(1863 - 1952). Spanish-born American philosopher and poet; a student of William James. Santayana attempted to reconcile Platonism and materialism, studied how reason works, and found "animal faith," or impulse, to be the basis of reason and belief.
Sartre, Jean-Paul
(1905 - 80). French philosopher, novelist, and dramatist; one of the founders of existentialism. Sartre was a Marxist through much of his life. He held that man is "condemned to be free" and to bear the responsibility of making free choices.
Schopenhauer, Arthur
(1788 - 1860). German post-Kantian philosopher who held that although irrational will is the driving force in human affairs, it is doomed not to be satisfied. He believed that only art and contemplation could offer escape from determinism and pessimism. Schopenhauer strongly influenced Nietzsche, Freud, Tolstoy, Proust, and Thomas Mann.
Scotus, John Duns
(c. 1266 - 1308). Scottish-born Scholastic philosopher who tried to integrate Aristotelian ideas into Christian theology. Scotus emphasized that all things depend not just on God's intellect but on divine will as well.
Smith, Adam
(1723 - 1790). Scottish philosopher and economist. He believed that if government left the marketplace to its own devices, an "invisible hand" would guarantee that the results would benefit the populace. Smith has had enormous influence on economists into the present day.
(464 - 399 B.C.). Athenian philosopher who allegedly wrote down none of his views, supposedly from his belief that writing distorts ideas. His chief student, Plato, is the major source of knowledge of what is known of his life. Socrates questioned Athenians about their moral, political, and religious beliefs, as depicted in Plato's dialogues; his questioning technique, called dialectic, has greatly influenced western philosophy. Socrates is alleged to have said that "the unexamined life is not worth living." In 399 B.C., he was brought to trial on charges of corrupting the youth and religious heresy. Sentenced to die, he drank poison.
Spinoza, Benedict (Baruch)
(1623 - 77). Dutch-born philosopher expelled from the Amsterdam Jewish community for heresy in 1656; he was attacked by Christian theologians 14 years later. In Ethics, Spinoza presents his views in a mathematical system of deductive reasoning. A proponent of monism, he held-in contrast to Descartes-that mind and body are aspects of a single substance, which he called God or nature.
Voltaire (Francois Marie Arouet)
(1694 - 1778). French philosopher, essayist, and historian; one of the major thinkers of the Enlightenment. A Deist who was anti-Christian, Voltaire widely advocated tolerance of liberal ideas and called for positive social action. His novel Cyandide is a parody of the optimism of Leibniz.
Whitehead, Alfred North
(1861 - 1947). British philosopher and mathematician who worked with Bertrand Russell. Whitehead tried to integrate twentieth-century physics into a metaphysics of nature.
William of Ockham (Occam)
(c. 1285 - c. 1349). Franciscan monk and important English theologian and philosopher. In his nominalism, he opposed much of the thought of St. Thomas Aquinas and of medieval Aristotelianism; he also rejected the Pope's power in the secular realm.

Famous Quotes

How to Argue Logically

We like to think that we speak logically all the time, but we are aware that we sometimes use illogical means to persuade others of our point of view. In the heat of an impassioned argument, or when we are afraid our disputant has a stronger case, or when we don't quite have all the facts we'd like to have, we are prone to engage in faulty processes of reasoning, using arguments we hope will appear sound.

Such defective arguments are called fallacies by philosophers who, starting with Aristotle, have catalogued and classified these fallacious arguments. There are now over 125 separate fallacies, most with their own impressive-sounding names, many of them in Latin.

Some arguments have easily recognizable defects. For instance, in the argument ad hominem, a person's views are criticized because of a logically irrelevant personal defect: "You can't take Smith's advice on the stock market; he's a known philanderer." In the genetic fallacy, something is mistakenly reduced to its origins: "We know that emotions are nothing more than physiology; after all, medical research has shown emotions involve the secretion of hormones." Another illogical argument is named for the erroneous thinking a wagering person may fall prey to, the gambler's fallacy (also called the Monte Carlo fallacy): "I'm betting on heads; it's got to come up since we've just had nine straight tails."

Some fallacies may not be recognized as erroneous reasoning because they are such commonly used forms of argument. For instance, if we say, "I'm sure my cold is due to the weather; I started sneezing right after it went from 60 degrees to 31 degrees in three hours," we are committing the fallacy with the Latin name of post hoc ergo propter hoc ("after this, therefore because of this"). Many a political argument exemplifies the fallacy of arguing in a circle; for instance: "Only wealthy men are capable of leading the country; after all, leadership can be learned only if you have had money to exercise power." Many prejudicial or stereotypical arguments commit the fallacy of division, or of applying to the part what may be true of the whole: "North Dakota has wide-open spaces; since Jack's farm is there, it must be quite large." The converse of this is the fallacy of composition, where properties of the parts are erroneously attributed to the whole: "Every apple on this tree is rotten; therefore, the tree itself is hopelessly diseased."

It may be a surprise to realize that some widely accepted forms of argument are just as fallacious as the most logically defective reasoning. When we appeal to the beliefs or behavior of the majority to prove the truth of something, we are committing the fallacy of consensus gentium: "Imbibing alcohol cannot be bad for people, since all cultures studied have used alcohol." Or consider the person who argues that "Tragedy is the highest form of literature; after all, didn't Aristotle consider it such?" This is a form of the fallacy of arguing from authority. There is also the fallacy of ignoratio elenchus, which has nothing to do with ignorance; its name means that the point made is irrelevant to the issue at hand, as in the untenable view of a lawyer who says, "Ladies and gentlemen of the jury, you cannot convict my client of manslaughter while driving under the influence; after all, advertisements for alcohol exist everywhere in our culture."



In logic, a fallacy is a form of reasoning that is illogical or that violates the rules of valid argumentation. A formal fallacy makes strict violations of the rules of logic. An informal fallacy does not violate the rules of logic, but it violates the rules of valid reasoning or arrives at unsound conclusions, because of unsound reasoning.

A common formal fallacy involves affirming the consequent or denying the antecedent in hypothetical reasoning. That is, if A, then B, affirming B as the proof of A, or denying A as the basis for denying B. In either case, it does not follow that the affirmation or the denial proves what is claimed. Thus, if all Americans are bald (A), then all Americans require no hairdressers (B)--the affirmation of B, that is, saying it is true, does not prove A; neither does the denial of A prove the denial of B.

Two other kinds of formal fallacies that are important are the argument from the undistributed middle and the conversion of a universal positive proposition. In the first, it is argued that "all A is B" and "all C is B"; therefore, "all A is C." If "Americans" is substituted for "A", "human beings" for "B", and "Hungarians" for "C", it is easily seen that the argument is fallacious. In the other case, it is argued that if "all A is B," then "all B is A"; this is obviously fallacious if the same substitutions are made.

Because informal fallacies occur much more frequently in ordinary discussions, in political speeches, and in advertising, they are, in some ways, more important. Some of these fallacies are a result of the ambiguity of the terms used; people often slip unconsciously from one meaning of a term to another. Other major informal fallacies are the ignoratio elenchi, that is, arguing for something different from the question asked; and the tu quoque argument, in which an unsound argument is justified by claiming the unsoundness of another. These soon degenerate into the argument ad hominem, in which the argument of an opponent is countered by pointing to his or her personal faults rather than by considering the substance of the argument; and the argument from authority, which appeals to famous or important people who agree with a particular point of view.

Richard H Popkin

Engel, S. Morris, With Good Reason: An Introduction to Informal Fallacies, 3d ed. (1985); Fearnside, W. Ward, and Holther, William B., Fallacy: The Counterfeit of Argument (1959).

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Philosophical Terms

The individual articles presented here were generally first published in the early 1980s. This subject presentation was first placed on the Internet in May 1997.

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