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Abelard, Peter ?(1079–1142). Abelard was an important and influential medieval French philosopher who contributed to logic and Christian theology. In 1113, he married his student Heloise, with whom he had fallen in love while he was in Paris teaching theology, in secret. The church would ultimately condemn him as a heretic because he was a nominalist when it came to universals.

Anaxagoras (ca. 500–428 B.C.). One of the most important of all the Presocratic philosophers, he was a teacher of Socrates and established Athens as the center of philosophy of the ancient world. Rejecting Empedocles’ theory of four elements, Anaxagoras contended that the basis of the material world was an infinite amount of tiny bits or particles and that every object is made up of these particles.

Anselm, St.? (1033–1109). One of the archbishops of Canterbury, St. Anselm was an Italian monk who became famous for his ontological argument for the existence of God and his treatise on the death of Christ titled Cur Deus Homo or Why the God-man? He is the founder of Scholasticism, which sought to combine Aristotelian logic with theology. Anselm also believed in the compatibility of human reason and divine revelation.

Aquinas, St. Thomas ?(1225–74). St. Thomas Aquinas is perhaps the greatest medieval theologian and philosopher and to this day serves as the model for Roman Catholic Theology. A member of the Scholastic School of philosophy, Aquinas endeavored to show how the teaching of Aristotle is compatible with church teaching. He also separated faith and reason into realms that were distinct but harmonious and complement one another. Aquinas’ philosophical proofs for God’s existence have been very influential.

Aristotle? (384–322 B.C.). Tutor to Alexander the Great, Aristotle’s contribution to Western philosophy is difficult to measure because of the vast influence he has had as a philosopher, logician, scientist, and as a student of many other subject areas. Aristotle looked at all things under the rubric of “the four causes,” and he was keen on observing nature to verify his hypotheses. In his Nicomachean Ethics, Aristotle defined virtue as the middle way between any two extremes. Although he opened a major school of philosophy in science in Athens in 335 B.C., Western Christendom did not have access to most of his works between about the fifth century and the twelfth century A.D.

Augustine of Hippo, St.? (354–430). St. Augustine towers over other figures in the Western Christian church as the greatest and most influential Christian theologian and philosopher after Paul of Tarsus. Augustine was adamant that human beings were helpless to please God apart from grace and is considered by many to be one of the first psychological thinkers due to his keen self-reflection in his Confessions. emphasized man's need for grace. His City of God is a foundational work in the philosophy of history.

Averroes? (1126–98). Born in Spain, Averroes commentaries on the philosophy of Aristotle were very important to educated people for over 300 years. A Muslim physician, lawyer, and philosopher, Averroes believed that faith and reason were compatible, although he asserted that reason alone was the source of philosophical knowledge. He emphasized the compatibility of faith and reason but believed philosophical knowledge to be derived from reason. Islam was uncomfortable with many of his ideas and the church later condemned him.

Avicenna ?(980–1037). Avicenna was a medieval Islamic philosopher who was indebted to Neoplatonism in his interpretations of Aristotle. His views influenced many thinkers, including St. Thomas Aquinas. The Persia-born Avicenna was also an important contributor to medicine; as a physician, his writings were influential in this area for almost 500 years.

Bacon, Sir Francis ?(1561–1626). Best-known for his embrace of the scientific method and the importance of inductive reasoning, Sir Francis Bacon was an English philosopher, statesman, and essayist. He is considered one of the fathers of British empiricism.

Boethius ?(c. 475–535). This Christian philosopher and statesman also translated many of Aristotle’s works. A Roman citizen, Boethius wrote The Consolation of Philosophy while he was in prison. This work on the role of reason amidst misfortune was very popular in the Middle Ages, and it provided a key tie between ancient philosophy and Scholastic philosophers and theologians.

Descartes, Rene ?(1596–1650). Modern philosophy often considers the French scientist and philosopher Rene Descartes to be its father. He is perhaps best known for throwing off the medieval view of authority in his quest for certainty, uttering “I think, therefore I am” (cogito ergo sum) when he found that the one think that he could not doubt was that he was a thinking being. He is also known for his application of mathematics to his philosophical pursuits.

Dewey, John? (1859–1952). The American philosopher John Dewey is one of the best known thinkers in the tradition of Pragmatism. He adapted the thinking of William James and Charles S. Pierce into his own form of pragmatic philosophy. Also serving as a psychologist and educational theorist, Dewey denied that knowledge came about passively and stressed the necessity of personal inquiry in the acquisition of understanding.

Hegel, Georg Wilhelm Friedrich (1770–1831). This German philosopher developed an idealistic form of metaphysics that would prove to be highly influential for decades into the twentieth century. He conceived of the world as one organism that advanced in three stages: a thesis would occur, then its opposite known as an antithesis, and then the thesis and antithesis would be combined into a new synthesis. Hegel said this embodied reason, and he also thought that monarchy was the most advanced version of government.

Heidegger, Martin ?(1889–1976). Martin Heidegger was a German philosopher who was indebted to the influence of Kierkegaard. He studied with Husserl and sought to understand the concept of “being,” focusing especially on the ways human beings act in the world and relate to it.

Hobbes, Thomasthis ?(1588–1679). Modern political philosophy counts Thomasthis Hobbes as one of its founders. One of Hobbes’ key contributions is the idea that people need a powerful, absolute ruler because of their inherent selfishness. He formulated the idea of the “social contract” wherein people surrender personal liberties to embrace the rule of the absolute ruler.

Hume, David? (1711–76). This British empiricist is best known for his arguments against miracles and the various proofs for God’s existence. David Hume believed that morals are solely the result of societal customs and could not be grounded in reason.

James, William ?(1842–1910). William James was a founder of the division of philosophy known as Pragmatism. An American, James wielded great influence as a psychologist and philosopher. He believed that truth was not eternally objective but merely an “expedient” way of thinking, and he thought that ideas did not reproduce our experiences from days gone buy. Instead, they guide our future actions and decisions. Consciousness, in his thinking, shapes and forms reality, and it does not merely interact with it.

Kant, Immanuel ?(1724–1804). Even though he was not widely influential in his own day, the German philosopher Immanuel Kant would become the most important thinkers of all time. Kant advocated a “critical philosophy” that was really a synthesis of the ideas of Hume and Leibniz. In this philosophy, Kant made human beings the center of knowledge: we know the world only as it conforms to the structures of our minds; our minds and thoughts do not conform to the outside world. Even though Kant believed freedom, immortality and God can not be proved via science or metaphysics, he said that all three of these are required for morality to exist.

Kierkegaard, Soren ?(1813–55). Soren Kierkegaard was a Danish Christian philosopher who is widely acknowledged to be the father of existentialism. He emphasized the idea that “truth is subjectivity,” lending credence to the view that religion is a private, individual affair. He also taught that suffering was an inevitable part of a person’s relationship to God.

Leibniz, Gottfried Wilhelm ?(1646–1716). Along with Sir Isaac Newton, Leibniz was one of the inventors of calculus. This German philosopher believed the universe was one, unified system that was an expression of the plan and design of God. He also served as a diplomat and mathematician.

Locke, John ?(1632–1704). John Locke was one of the key figures in British empiricism, and many people regard him as the founder of that system of philosophy. As a strong empiricist, Locke did not believe in any innate ideas but held that they all came from our experience. Political authority, in his thinking, comes solely from the consent of those that are governed, a view that was incredibly influential in the American Revolution and the U.S. Constitution.

Machiavelli, Niccolo ?(1469–1527). Most famous for his political book The Prince, Machiavelli ranks among the chief political writers of history. This Italian Renaissance statesman and thinker contended that rulers could engage in any act that was necessary to achieve and sustain their power; consequently, we commonly refer to all cunning and power-hungry political tactics as Machiavellian.

Maimonides ?(1135 – 1204). Maimonides was a medieval Jewish philosopher from Spain who worked to combine Aristotelian philosophy with Judaic theology. He continues to be an influential thinker within Judaism, and Christian thought has benefitted from his work as well.

Marx, Karl ?(1818–83). This German economist and philosopher was a poor family man, but his ideas were foundational for the socialism and communism of the nineteenth and twentieth centuries. Marx’s theories, which he developed along with Engels, continue to be felt even today. He was a materialist philosopher who was initially attracted to the idealism of Hegel, and his works Das Kapital and The Communist Manifesto have decisively shaped world history.

Mill, John Stuart ?(1806–73). Mill was an English thinker in the tradition of British Empiricism. A strong advocate for individual rights, Mill expressed his political ideas in On Liberty, his guidelines for scientific thinking in System of Logic, and followed in Jeremy Bentham’s trajectory of utilitarian ethics.

Moore, G. E. (George Edward)? (1873–1958). This British philosopher and thinker held to the “common sense” view when it came to question of material objects and their reality. More also made important contributions to ethical thought, teaching that goodness can only be known by moral intuition and nwas an important and influential medieval French philosopher who contributed to logic and Christian theology. In 1113, he married his student Heloise, with whom he had fallen in love while he was in Paris teaching theology, in secret. The church would ultimately condemn him as a heretic because he was a nominalist when it came to universals. Anaxagoras (ca. 500–428 B.C.). One of the most important of all the Presocratic philosopheothing else.

More, Sir Thomas? (1478–1535). More was an important Renaissance humanist who served as Lord Chancellor of England. He was a strong advocate for the reform of society, and in his work Utopia, he described what he believed was the ideal state of peaceful governance. Eventually he lost his head because he would not confess the king as head of the church.

Nietzsche, Friedrich Wilhelm ?(1844–1900). This influential German philosopher, poet, and philologist is a foundational thinker for both nihilism and postmodernism. Nietzsche rejected traditional Christian values in favor of the ubermensch or “superman” who would create a new ethic through his “will to power.” He is also famous for his statement “God is dead,” which was more an observation about the superficial nature of late nineteenth-century European religion than an affirmation of his own atheism.

Pascal, Blaise ?(1623–62). Blaise Pascal was a French philosopher and theologian who made important contributions to mathematics and science. In his work Pensees (“Thoughts”), Pascal asserts that reason alone cannot meet the needs of human beings, who can know God only via mystic understanding.

Plato? (c. 428–c. 348 B.C.). Plato is perhaps the most well-known and influential Western philosopher. A student of Socrates, Plato established an Academy in Athens and taught there until his death. Plato set forth his views in many works that take the form of dialogues in the form of dialogues between Socrates and other Greek citizens. The Republic summarizes many of the views of Plato, especially his political view that the ideal state is ruled by a philosopher king who receives advanced training in morals and mathematics. In his other dialogues, Plato explored epistemology, immortality, morality, and cosmology.

Plotinus? (205–270). Plotinus was born in Egypt and founded the school of thought of Neoplatonism. His synthesis of Plato’s thinking and the theories of other Greek thinkers asserted that the universe results from a series of emanations from a font of pure being, with the emanations furthest from the source being of a lesser order than those closer to the source. It is commonly asserted that Plotinus had a decisive influence on Christian theology, but many theologians would dispute how extensive this influence truly was.

Rousseau, Jean Jacques ?(1712–1778). Rosseau was a Genevan-born thinker who believed that mankind is inherently and naturally good. His influence has been strongly felt in the Romantic movement and educational theory, as well as in political thought where in The Social Contract he defined governments as the result of the choice of people for the common good.was an important and influential medieval French philosopher who contributed to logic and Christian theology. In 1113, he married his student Heloise, with whom he had fallen in love while he was in Paris teaching theology, in secret. The church would ultimately condemn him as a heretic because he was a nominalist when it came to universals. Anaxagoras (ca. 500–428 B.C.). One of the most important of all the Presocratic philosophe

Russell, Bertrand ?(1872–1970). Bertrand Russell was an English philosopher, pacifist, and vociferous agnostic critic of Christianity. Along with Alfred North Whitehead, Russell helped to establish modern logic, and he was not afraid to change his views in his quest to defend epistemology as a science.

Santayana, George? (1863–1952). This student of William James was born in Spain but later did his work in America. A poet and philosopher, Santayana investigated human reason, tried to reconcile materialism with Platonism, and he believed that impulse or “animal faith” was the foundation of all belief and reason.

Sartre, Jean-Paul ?(1905–80). Sarte ranks among the most important of all the existentialist philosophers. He was a French philosopher and accomplished author of novels plays, many of which express his view that human beings are “condemned to be free” and be responsible for their decisions. He also embraced Marxism for most of his life.

Schopenhauer, Arthur ?(1788–1860). Arthur Schopenhauer located irrational will as the foundation for all human affairs, but he also believed this driving force could never be satisfied. A German philosopher, he taught that contemplation and art are the only way human beings can free themselves from pessimism and determinism. His thinking was greatly influential in the lives of Freud, Proust, Nietzsche, Tolstoy, and Thomas Mann.

Scotus, John Duns? (c. 1266–1308). Like the other Scholastic philosophers, Scotus worked to integrate Aristotle’s teaching with Christian dogma. Born in Scotland, Scotus believed that everything depends both on the mind of God and on the will of God.

Smith, Adam? (1723–1790). Adam Smith is one of the most important economic thinkers of all times. He is known for his assertion of the “invisible hand” of the free market that would benefit all people as long as the government stayed out of it. Western capitalism is highly dependent on the thinking of this Scottish philosopher.

Socrates? (464–399 B.C.). Socrates believed that writing distorts a teacher’s ideas and so he never wrote them down. Ironically, however, his ideas and name have become synonymous with Western philosophy. Most of what we know about this Athenian philosopher comes from his student Plato who preserves much information about Socrates in the various dialogues he wrote. Socrates method of questioning about morals, politics, and religion known as dialectic has been important in Western thought, and he is also the source of the famous quote “the unexamined life is not worth living.” Socrates died after was sentenced to drink poison on the charge that he was corrupting the youth of Athens.

Spinoza, Benedict (Baruch) ?(1623–77). Spinoza was a Dutch, Jewish philosopher who was eventually rejected as a heretic by the Jewish community in Amsterdam. His writings also offended Christian theologians after his expulsion. Spinoza is one of the forefathers of the modern critical study of the Bible and held a monistic view of reality wherein mind and body are both aspects of a single essence known as God or nature. His Ethics is the source of much of what we know about Spinoza’s thinking.

Voltaire (Francois Marie Arouet)? (1694–1778). No study of Enlightenment thought would be complete without a mention of this French historian, essayist and philosopher. Voltaire was a deist with strong anti-Christian views, although he was a strong advocate for the liberal ideas of free speech and positive social action. In his novel Candide, Voltaire parodied Leibiniz’s famous optimism.

Whitehead, Alfred North? (1861–1947). Alfred North Whitehead is the founder of process philosophy that was later embraced by some theologians in the school of Process Theology. This British philosopher and mathematician worked with Bertrand Russell, and he tried to form his metaphysics on the basis of twentieth-century discoveries in physics.

William of Ockham (Occam) ?(c. 1285–c. 1349). Famous for his “Occam’s Razor,” this English philosopher was one of the few churchmen of the medieval period who denied the power of the pope in the secular world. A Franciscan monk, he was also a nominalist who opposed many of the ideas of medieval Aristotelian philosophy and the thinking of St. Thomas Aquinas.