History of Western Philosophy

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Philosophy, Western (Greek philosophia,"love of wisdom"), the rational and critical inquiry into basic principles. Philosophy is often divided into four main branches: metaphysics, the investigation of ultimate reality; epistemology, the study of the origins, validity, and limits of knowledge; ethics, the study of the nature of morality and judgment; and aesthetics, the study of the nature of beauty in the fine arts. The two distinctively philosophical types of inquiry are analytic philosophy, which is the logical study of concepts, and synthetic philosophy, which is the arrangement of concepts into a unified system.

As used originally by the ancient Greeks, the term philosophy meant the pursuit of knowledge for its own sake. Philosophy comprised all areas of speculative thought and included the arts, sciences, and religion. As special methods and principles were developed in the various areas of knowledge, each area acquired its own philosophical aspect, giving rise to the philosophy of art, of science, and of religion. The term philosophy is often used popularly to mean a set of basic values and attitudes toward life, nature, and society—thus the phrase "philosophy of life." Because the lines of distinction between the various areas of knowledge are flexible and subject to change, the definition of the term philosophy remains a subject of controversy.

Western philosophy from Greek antiquity to modern times is surveyed in the remainder of this article. For information about philosophical thought in the Far and Middle East, see Chinese Philosophy; Islam; Buddhism; Daoism (Taoism); Confucianism.

Western philosophy is considered generally to have begun in ancient Greece as speculation about the underlying nature of the physical world. In its earliest form it was indistinguishable from natural science. The writings of the earliest philosophers no longer exist, except for a few fragments cited by Aristotle and by other writers of later times.

 The Ionian School  The first philosopher of historical record was Thales of the city of Miletus, on the Ionian coast of Asia Minor, who practiced about 580BC. Thales, who was revered by later generations as one of the Seven Wise Men of Greece, was interested in astronomical, physical, and meteorological phenomena, and his scientific investigations led him to speculate that all natural phenomena are different forms of one fundamental substance, which he believed to be water, because he thought evaporation and condensation to be universal processes. Anaximander, a disciple of Thales, maintained that the first principle from which all things evolve is an intangible, invisible, infinite substance that he called apeiron,"the boundless." He realized, however, that no observable substance could be found in all things; thus his notion of the boundless anticipated the modern notion of an unbounded universe. This substance, he maintained, is eternal and indestructible. Out of its ceaseless motion the more familiar substances, such as warmth, cold, earth, air, and fire, continuously evolve, generating in turn the various objects and organisms that make up the recognizable world.

The third great Ionian philosopher, Anaximenes, returned to Thales' assumption that the primary substance is something familiar and material, but he claimed it to be air rather than water. He believed that the changes things undergo could be explained in terms of rarefaction and condensation of air. Thus Anaximenes was the first philosopher to explain qualitative differences in terms of quantitative differences, a method fundamental to physical science.

In general, the Ionian school made the initial radical step from mythological to scientific explanation of natural phenomena; it discovered the important scientific principles of the permanence of substance, the natural evolution of the world, and the reduction of quality to quantity.

 The Pythagorean School  
About 530BC the philosopher Pythagoras founded at Crotona, in southern Italy, a school of philosophy that was more religious and mystical than the Ionian school. It fused the ancient mythological view of the world with the developing interest in scientific explanation. The system of philosophy that became known as Pythagoreanism combined ethical, supernatural, and mathematical beliefs into a spiritualistic view of life. The Pythagoreans taught and practiced a way of life based on the belief that the soul is a prisoner of the body, is released from the body at death, and reincarnated in a higher or lower form of life, depending on the degree of virtue achieved. The highest purpose of humans should be to purify their souls by cultivating intellectual virtues, refraining from sensual pleasures, and practicing various religious rituals. The Pythagoreans, having discovered the mathematical laws of musical pitch, inferred that planetary motions produce a "music of the spheres," and developed a "therapy through music" to bring humanity in harmony with the celestial spheres. They identified science with mathematics, maintaining that all things are made up of numbers and geometrical figures. They made important contributions to mathematics, musical theory, and astronomy.

 The Heraclitean School  Heraclitus of Ephesus, continuing the search of the Ionians for a primary substance, claimed it to be fire. He noticed that heat produces changes in matter, and thus anticipated the modern theory of energy. Heraclitus maintained that all things are in a state of continuous flux, that stability is an illusion, and that only change and the law of change, or Logos, are real. The Logos doctrine of Heraclitus, which identified the laws of nature with a divine mind, developed into the pantheistic theology of Stoicism.

 The Eleatic School  In the 5th century BC, Parmenides founded a school of philosophy at Elea, a Greek colony on the Italian peninsula. Parmenides took a position opposite from that of Heraclitus on the relation between stability and change, maintaining that the universe, or the state of being, is an indivisible, unchanging, spherical entity and that all reference to change or diversity is self-contradictory. Nothing, he claimed, can be truly asserted except that "being is."Zeno of Elea, a disciple of Parmenides, tried to prove the unity of being by arguing that the belief in the reality of change, diversity, and motion leads to logical paradoxes. The paradoxes of Zeno became famous intellectual puzzles that philosophers and logicians of all subsequent ages have tried to solve. The concern of the Eleatics with the problem of logical consistency laid the basis for the development of the science of logic.

 The Pluralists  The speculation about the physical world begun by the Ionians was continued in the 5th century BC by Empedocles and Anaxagoras, who developed a philosophy replacing the Ionian assumption of a single primary substance with an assumption of a plurality of such substances. Empedocles maintained that all things are composed of four irreducible elements: air, water, earth, and fire, which are alternately combined and separated by two opposite forces, love and strife. By that process the world evolves from chaos to form and back to chaos again, in an eternal cycle. Empedocles regarded the eternal cycle as the proper object of religious worship and criticized the popular belief in personal deities, but he failed to explain the way in which the familiar objects of experience could develop out of elements that are totally different from them. Anaxagoras therefore suggested that all things are composed of very small particles, or "seeds," which exist in infinite variety. To explain the way in which these particles combine to form the objects that constitute the familiar world, Anaxagoras developed a theory of cosmic evolution. He maintained that the active principle of this evolutionary process is a world mind that separates and combines the particles. His concept of elemental particles led to the development of an atomic theory of matter.

 The Atomists  It was a natural step from pluralism to atomism, the theory that all matter is composed of tiny, indivisible particles differing only in simple physical properties such as size, shape, and weight. This step was taken in the 4th century BC by Leucippus and his more famous associate Democritus, who is generally credited with the first systematic formulation of an atomic theory of matter. His conception of nature was thoroughly materialistic, explaining all natural phenomena in terms of the number, shape, and size of atoms. He thus reduced the sensory qualities of things, such as warmth, cold, taste, and odor, to quantitative differences among atoms.The higher forms of existence, such as plant and animal life and even human thought, were explained by Democritus in these purely physical terms. He applied his theory to psychology, physiology, theory of knowledge, ethics, and politics, thus presenting the first comprehensive statement of deterministic materialism, in which all aspects of existence are claimed to be rigidly determined by physical laws.

 The Sophists  Toward the end of the 5th century BC, a group of traveling teachers called Sophists became famous throughout Greece. The Sophists played an important role in developing the Greek city-states from agrarian monarchies into commercial democracies. As Greek industry and commerce expanded, a class of newly rich, economically powerful merchants began to wield political power. Lacking the education of the aristocrats, they sought to prepare themselves for politics and commerce by paying the Sophists for instruction in public speaking, legal argument, and general culture. Although the best of the Sophists made valuable contributions to Greek thought, the group as a whole acquired a reputation for deceit, insincerity, and demagoguery. Thus the word sophistry has come to signify these moral faults. The famous maxim of Protagoras, one of the leading Sophists, that "man is the measure of all things," is typical of the philosophical attitude of the Sophist school. Sophists held that individuals have the right to judge all matters for themselves. They denied the existence of an objective knowledge that everyone can be expected to believe, asserted that natural science and theology are of little or no value because they have no impact on daily life, and declared that ethical rules need be followed only when it is to one's practical advantage to do so.

 Socratic Philosophy  
Perhaps the greatest philosophical personality in history was Socrates. Born in 469BC, Socrates maintained a philosophical dialogue with his students until he was condemned to death and took his own life in 399BC. Unlike the Sophists, Socrates refused to accept payment for his teachings, maintaining that he had no positive knowledge to offer, except the awareness of the need for more knowledge. Socrates left no writings as records of his thought, but his teachings were preserved for later generations in the dialogues of his famous pupil Plato. Socrates taught that every person has full knowledge of ultimate truth contained within the soul and needs only to be spurred to conscious reflection in order to become aware of it. In Plato's dialogue Meno, for example, Socrates guides an untutored slave to the formulation of the Pythagorean theorem, thus demonstrating that such knowledge is innate in the soul, rather than learned from experience. The philosopher's task, Socrates believed, was to provoke people into thinking for themselves, rather than to teach them anything they did not already know. His contribution to the history of thought was not a systematic doctrine but a method of thinking and a way of life. He stressed the need for analytical examination of the grounds of one's beliefs, for clear definitions of basic concepts, and a rational and critical approach to ethical problems.

 Platonic Philosophy  
Plato was a more systematic and positive thinker than Socrates, but his writings, particularly the earlier dialogues, can be regarded as a continuation and elaboration of Socratic insights. Like Socrates, Plato regarded ethics as the highest branch of knowledge; he stressed the intellectual basis of virtue, identifying virtue with wisdom. This view led to the so-called Socratic paradox that, as Socrates asserts in the Protagoras, "no man does evil voluntarily." Aristotle later noticed that such a conclusion allows no place for moral responsibility. Plato also explored the fundamental problems of natural science, political theory, metaphysics, theology, and theory of knowledge, and developed ideas that became permanent elements in Western thought.

The basis of Plato's philosophy is his theory of Ideas, or doctrine of Forms. The theory of Ideas, which is expressed in many of his dialogues, particularly the Republic and the Parmenides, divides existence into two realms, an "intelligible realm" of perfect, eternal, and invisible Ideas, or Forms, and a "sensible realm" of concrete, familiar objects. Trees, stones, human bodies, and other objects that can be known through the senses are for Plato unreal, shadowy, and imperfect copies of the Ideas. He was led to this apparently bizarre conclusion by his high standard of knowledge, which required that all genuine objects of knowledge be described without contradiction. Because all objects perceived by the senses undergo change, an assertion made about such objects at one time will not be true at a later time. According to Plato, these objects are not completely real. Beliefs derived from experience of such objects are therefore vague and unreliable, whereas the principles of mathematics and philosophy, discovered by inner meditation on the Ideas, constitute the only knowledge worthy of the name. In the Republic, Plato described humanity as imprisoned in a cave and mistaking shadows on the wall for reality; he regarded the philosopher as the person who penetrates the world outside the cave of ignorance and achieves a vision of the true reality, the realm of Ideas. Plato's concept of the Absolute Idea of the Good, which is the highest Form and includes all others, has been a main source of pantheistic and mystical religious doctrines in Western culture.

Plato's theory of Ideas and his rationalistic view of knowledge formed the foundation for his ethical and social idealism. The realm of eternal Ideas provides the standards or ideals according to which all objects and actions should be judged. The philosophical person, who refrains from sensual pleasures and searches instead for knowledge of abstract principles, finds in these ideals the modes for personal behavior and social institutions. Personal virtue consists in a harmonious relation among the faculties of the soul. Social justice consists in harmony among the classes of society. The ideal state of a sound mind in a sound body requires that the intellect control the desires and passions, as the ideal state of society requires that the wisest individuals rule the pleasure-seeking masses. Truth, beauty, and justice coincide in the Idea of the Good, according to Plato; therefore, art that expresses moral values is the best art. In his rather conservative social program, Plato supported the censorship of art, regarding art as an instrument for the moral education of youth.

 Aristotelian Philosophy  
Aristotle, who began study at Plato's academy at age 17 in 367 BC, was the most illustrious pupil of Plato, and ranks with his teacher among the most profound and influential thinkers of the Western world. After studying for many years at Plato's Academy, Aristotle became the tutor of Alexander the Great. He later returned to Athens to found the Lyceum, a school that, like Plato's Academy, remained for centuries one of the great centers of learning in Greece. In his lectures at the Lyceum, Aristotle defined the basic concepts and principles of many of the theoretical sciences, such as logic, biology, physics, and psychology. In founding the science of logic, he developed the theory of deductive inference, represented by the syllogism (a deductive argument having two premises and a conclusion), and a set of rules for scientific method.

In his metaphysical theory, Aristotle criticized Plato's separation of form from matter and maintained that the Forms, or essences, are contained within the concrete objects that exemplify them. Everything real, for Aristotle, is a combination of potentiality and actuality; in other words, everything is a combination of that which a thing may be, but is not yet, and that which it already is (also distinguished as matter and form), because all things change and become other than they were, except the human and divine active intellects, which are pure forms.

Nature, for Aristotle, is an organic system of things whose common forms make it possible to arrange them into classes comprising species and genera, each species having a form, purpose, and mode of development in terms of which it can be defined. The aim of theoretical science is to define the essential forms, purposes, and modes of development of all species and to arrange them in their natural order in accordance with their complexities of form, the main levels being the inanimate, the vegetative, the animal, and the rational. The soul, for Aristotle, is the form, or actuality, of the body, and humans, whose rational soul is a higher form than the souls of other terrestrial species, are the highest species of perishable things. The heavenly bodies, composed of an imperishable substance, or ether, and moved eternally in perfect circular motion by God, are still higher in the order of nature. This hierarchical classification of nature was adopted by many Christian, Jewish, and Muslim theologians in the Middle Ages as a view of nature consistent with their religious beliefs.

Aristotle's political and ethical philosophy similarly developed out of a critical examination of Platonic principles. The standards of personal and social behavior, according to Aristotle, must be found in the scientific study of the natural tendencies of individuals and societies rather than in a heavenly realm of pure forms. Less insistent therefore than Plato on a rigorous conformity to absolute principles, Aristotle regarded ethical rules as practical guides to a happy and well-rounded life. His emphasis on happiness, as the active fulfillment of natural capacities, expressed the attitude toward life held by cultivated Greeks of his time. In political theory, Aristotle took a more realistic position than Plato. He agreed that a monarchy ruled by a wise king would be the ideal political structure, but recognized that societies differ in their needs and traditions and believed that a limited democracy is usually the best compromise. In his theory of knowledge, Aristotle rejected the Platonic doctrine that knowledge is innate and insisted that it can be acquired only by generalization from experience. He interpreted art as a means of pleasure and intellectual enlightenment rather than an instrument of moral education. His analysis of Greek tragedy has served as a model of literary criticism (see Criticism, Literary).

From the 4th century BC to the rise of Christian philosophy in the 4th century AD, Epicureanism, Stoicism, skepticism, and Neoplatonism were the main philosophical schools in the Western world. Interest in natural science declined steadily during this period, and these schools were concerned mainly with ethics and religion.

 Epicureanism  In 306BC Epicurus founded a philosophical school in Athens. Because his followers met in the garden of his home they became known as "philosophers of the garden." Epicurus adopted the atomistic physics of Democritus but made several important changes. In place of the random motion of the atoms in all directions, he assumed, for simplicity of explanation, that a uniform motion downward occurred. He also allowed an element of chance in the physical world by assuming that the atoms sometimes swerve in unpredictable ways, thus providing a physical basis for a belief in free will. He maintained that natural science is important only if it can be applied in making practical decisions and in allaying fear of the gods or of death. The aim of human life, he claimed, is to achieve the maximum amount of pleasure, which he identified with gentle motion and the absence of pain. The teachings of Epicurus are preserved mainly in the philosophical poem On the Nature of Things by the Roman poet Lucretius, who contributed greatly to the popularity of Epicureanism in Rome.

The Stoic school, founded in Athens about 310BC by Zeno of Citium, developed out of the earlier movement of the Cynics, who rejected social institutions and material values. Stoicism became the most influential school of the Greco-Roman world, producing such remarkable writers and personalities as the Greek slave and later Roman philosopher Epictetus and the Roman emperor Marcus Aurelius, who was noted for his wisdom and his nobility of character. The Stoics taught that one can achieve freedom and tranquillity only by becoming insensitive to material comforts and external fortune and by dedicating oneself to a life of reason and virtue. Holding a somewhat materialistic conception of nature, they followed Heraclitus in believing the primary substance to be fire and in worshiping the Logos, which they identified with the energy, law, reason, and providence found throughout nature. Human reason was also considered part of the divine Logos, and therefore immortal. The Stoic doctrine that each person is part of God and that all people form a universal family helped to break down national, social, and racial barriers and to prepare the way for the spread of a universal religion. The Stoic doctrine of natural law, which makes human nature the standard for evaluating laws and social institutions, had an important influence on Roman and later Western law.

The school of skepticism, which continued the Sophist criticisms of objective knowledge, dominated the Platonic Academy in the 3rd century BC. The skeptics discovered, as had Zeno of Elea, that logic is a powerful critical device, capable of destroying any positive philosophical view, and they used it skillfully. Their fundamental assumption was that humanity cannot attain knowledge or wisdom concerning reality and that the way to happiness therefore lies in a complete suspension of judgment. As an extreme example of this attitude, it is said that Pyrrho, one of the most noted skeptics, refused to change direction when approaching a cliff and had to be diverted by his students. Carneades maintained that beliefs acquired inductively from experience can be probable, but never certain.

 Neoplatonism  The Jewish-Hellenistic philosopher Philo Judaeus combined Greek philosophy, particularly Platonic and Pythagorean ideas, with Judaic religion in a comprehensive system that anticipated Neoplatonism and Jewish, Christian, and Muslim mysticism. Philo insisted on the transcendent nature of God as surpassing human understanding and therefore indescribable; he described the natural world as a series of stages of descent from God, terminating in matter as the source of evil. He advocated a religious state, or theocracy, and was one of the first to interpret the Old Testament for the Gentiles. Judaeus died around AD50.

Neoplatonism, one of the most influential philosophical and religious schools and an important rival of Christianity, was founded in the 3rd century AD by Ammonius Saccus and his more famous disciple Plotinus. Plotinus based his ideas on the mystical and poetic writings of Plato, the Pythagoreans, and Philo. The main function of philosophy, for him, is to prepare individuals for the experience of ecstasy, in which they become one with God. God, or the One, is beyond rational understanding and is the source of all reality. The universe emanates from the One by a mysterious process of overflowing of divine energy, in successive levels. The highest levels form a trinity of the One; the Logos, which contains the Platonic Forms; and the World Soul, which gives rise to human souls and natural forces. The farther things emanate from the One, according to Plotinus, the more imperfect and evil they are and the closer they approach the limit of pure matter. The highest goal of life is to purify oneself of dependence on bodily comforts and, through philosophical meditation, to prepare oneself for an ecstatic reunion with the One. Neoplatonism exerted a strong influence on medieval thought.

During the decline of Greco-Roman civilization, Western philosophers turned their attention from the scientific investigation of nature and the search for worldly happiness to the problem of salvation in another and better world. By the 3rd century AD, Christianity had spread to the more educated classes of the Roman Empire. The religious teachings of the Gospels were combined by the Fathers of the Church with many of the philosophical concepts of the Greek and Roman schools.

 Augustinian Philosophy  
The process of reconciling the Greek emphasis on reason with the emphasis on religious emotion in the teachings of Christ and the apostles found eloquent expression in the writings of Saint Augustine. He developed a system of thought that, through subsequent amendments and elaborations, eventually became the authoritative doctrine of Christianity. Largely as a result of his influence, Christian thought was Platonic in spirit until the 13th century, when Aristotelian philosophy became dominant. Augustine argued that religious faith and philosophical understanding are complementary rather than opposed and that one must "believe in order to understand and understand in order to believe." Like the Neoplatonists, he considered the soul a higher form of existence than the body and taught that knowledge consists in the contemplation of Platonic ideas that have been purified of both sensation and imagery.

The Platonic philosophy was combined with the Christian concept of a personal God who created the world and predestined its course, and with the doctrine of the fall of humanity, requiring the divine incarnation in Christ. Augustine attempted to provide rational solutions to the problems of free will and predestination, the existence of evil in a world created by a perfect and all-powerful God, and the three persons in one nature attributed to God in the doctrine of the Trinity.

Saint Augustine conceived of history as a dramatic struggle between the good in humanity, as expressed in loyalty to the "city of God," or community of saints, and the evil in humanity, as embodied in the earthly city with its material values. His view of human life was profoundly pessimistic, asserting that happiness is impossible in the world of the living, where even with good fortune, which is rare, awareness of approaching death would mar any tendency toward satisfaction. He believed further that without the religious virtues of faith, hope, and charity, which require divine grace to be attained, a person cannot develop the natural virtues of courage, justice, temperance, and wisdom. His analyses of time, memory, and inner religious experience have been a source of inspiration for metaphysical and mystical thought.

The only major contribution to Western philosophy in three centuries following the death of Augustine was made by the 6th-century Roman statesman Boethius, who revived interest in Greek and Roman philosophy, particularly Aristotle's logic and metaphysics. In the 9th century the Irish monk John Erigena developed a pantheistic interpretation of Christianity, identifying the divine Trinity with the One, Logos, and World Soul of Neoplatonism and maintaining that both faith and reason are necessary to achieve the ecstatic union with God.

In the 11th century a revival of philosophical thought began as a result of the increasing contact between different parts of the Western world and the general reawakening of cultural interests that culminated in the Renaissance. The works of Plato, Aristotle, and other Greek thinkers were translated by Arab scholars and brought to the attention of philosophers in Western Europe. Muslim, Jewish, and Christian philosophers interpreted and clarified these writings in an effort to reconcile philosophy with religious faith and to provide rational grounds for their religious beliefs. Their labors established the foundations of Scholasticism.

Scholastic thought was less interested in discovering new facts and principles than in demonstrating the truth of existing beliefs. Its method was therefore dialectical, or argumentative. Intense concern with the logic of argument led to important developments in logic as well as theology. The 11th-century Arab physician Avicenna united Neoplatonic and Aristotelian ideas with Muslim religious doctrine, and the Jewish poet Solomon ben Yehuda Ibn Gabirol made a similar synthesis of Greek thought and Judaism. The ecclesiastic and Scholastic philosopher Anselm of Canterbury adopted Augustine's view of the relation between faith and reason and combined Platonism with Christian theology. Supporting the Platonic theory of Ideas, Anselm argued in favor of the separate existence of universals, or common properties of things. He thus established the position of logical realism on one of the most vigorously disputed issues of medieval philosophy.

The contrary view, known as nominalism, was formulated by the Scholastic philosopher Roscelin, who maintained that only individual, concrete objects exist and that the universals, forms, and ideas, under which particular things are classified, constitute mere sounds or marks, rather than intangible substances. When he argued that the Trinity must consist of three separate beings, his views were deemed heretical and he was forced to recant in 1092. The French Scholastic theologian Peter Abelard, whose tragic love affair with Héloïse in the 12th century is one of the most memorable romantic stories in medieval history, proposed a compromise between realism and nominalism known as conceptualism, according to which universals exist in particular things as properties and outside of things as concepts in the mind. Abelard maintained that revealed religion must be justified by reason. He developed an ethics based on personal conscience that anticipated Protestant thought.

The Spanish-Arab jurist and physician Averroës, the most noted Muslim philosopher of the Middle Ages, made Aristotelian science and philosophy a powerful influence on medieval thought with his lucid and scholarly commentaries on the works of Aristotle. He earned himself the title "the Commentator" among the many Scholastics who came to regard Aristotle as "the Philosopher." Averroës attempted to overcome the contradictions between Aristotelian philosophy and revealed religion by distinguishing between two separate systems of truth, a scientific body of truths based on reason and a religious body of truths based on revelation. His view that reason takes precedence over religion led to his exile in 1195. Averroës's so-called double-truth doctrine influenced many Muslim, Jewish, and Christian philosophers; it was rejected, however, by many others, and became an important issue in medieval philosophy.

The Jewish rabbi and physician Moses Maimonides, one of the greatest figures in Judaic thought, followed Averroës in uniting Aristotelian science with religion but rejected the view that both of two conflicting systems of ideas can be true. In his Guide for the Perplexed (1180) Maimonides attempted to provide a rational explanation of Judaic doctrine and defended religious beliefs (such as the belief in the creation of the world) that conflicted with Aristotelian science only when he was convinced that decisive evidence was lacking on either side.

The English Scholastic theologian Alexander of Hales and the Italian Scholastic philosopher Saint Bonaventure, both philosophers of the 13th century, combined Platonic and Aristotelian principles and introduced the concept of substantial form, or nonmaterial substance, to account for the immortality of the soul. Bonaventure's view tended toward pantheistic mysticism in making the end of philosophy the ecstatic union with God.

The German Scholastic philosopher Saint Albertus Magnus was the first Christian philosopher to endorse and interpret the entire system of Aristotelian thought. He studied and admired the writings of the Muslim and Jewish Aristotelians and wrote encyclopedic commentaries on Aristotle and the natural science of his day. Albertus Magnus died in 1280. The English monk Roger Bacon, one of the first Scholastics to take an interest in experimental science, realized that a great deal remained to be learned about nature. He criticized the deductive method of his contemporaries and their reliance on past authority, and called for a new method of inquiry based on controlled observation.

The greatest intellectual figure of the medieval era was Saint Thomas Aquinas, a Dominican monk who studied under Albertus Magnus, following him to Cologne in 1248. Aquinas combined Aristotelian science and Augustinian theology into a comprehensive system of thought that later became the authoritative philosophy of the Roman Catholic church. He wrote on every known subject in philosophy and science, and his major works, Summa Theologica and Summa Contra Gentiles, in which he presents a persuasive and systematic structure of ideas, still constitute a powerful influence on Western thought. His writings reflect the renewed interest of his time in reason, nature, and worldly happiness, together with its religious faith and concern for salvation.

Aquinas argued against the Averroists that the truths of faith and the truths of reason cannot conflict but rather apply to different realms. The truths of natural science and philosophy are discovered by reasoning from facts of experience, whereas the tenets of revealed religion, the doctrine of the Trinity, the creation of the world, and other articles of Christian dogma are beyond rational comprehension, although not inconsistent with reason, and must be accepted on faith. The metaphysics, theory of knowledge, ethics, and politics of Aquinas were derived mainly from Aristotle, but he added the Augustinian virtues of faith, hope, and charity and the goal of eternal salvation through grace to Aristotle's naturalistic ethics with its goal of worldly happiness.

  Medieval Philosophy After Aquinas  The most important critics of Thomistic philosophy (adherence to the theories of Aquinas) were John Duns Scotus and William of Ockham. Duns Scotus developed a subtle and highly technical system of logic and metaphysics, but because of the fanaticism of his followers the name Duns later ironically became a symbol of stupidity in the English word dunce. Scotus rejected the attempt of Aquinas to reconcile rational philosophy with revealed religion. He maintained, in a modified version of the so-called double-truth doctrine of Averroës, that all religious beliefs are matters of faith, except for the belief in the existence of God, which he regarded as logically provable. Against the view of Aquinas that God acts in accordance with his rational nature, Scotus argued that the divine will is prior to the divine intellect and creates, rather than follows, the laws of nature and morality, thus implying a stronger notion of free will than that of Aquinas. On the issue of universals, Duns Scotus developed a new compromise between realism and nominalism, accounting for the difference between individual objects and the forms that these objects exemplify as a logical rather than a real distinction. Duns Scotus died in 1308.

The English Scholastic William of Ockham formulated the most radically nominalistic criticism of the Scholastic belief in intangible, invisible things such as forms, essences, and universals. He maintained that such abstract entities are merely references of words to other words rather than to actual things. His famous rule, known as Ockham's razor—which said that one should not assume the existence of more things than are logically necessary—became a fundamental principle of modern science and philosophy.

In the 15th and 16th centuries a revival of scientific interest in nature was accompanied by a tendency toward pantheistic mysticism. The Roman Catholic prelate Nicholas of Cusa anticipated the work of the Polish astronomer Nicolaus Copernicus in his suggestion that the earth moved around the sun, thus displacing humanity from the center of the universe; he also conceived of the universe as infinite and identical with God. The Italian philosopher Giordano Bruno, who similarly identified the universe with God, developed the philosophical implications of the Copernican theory. Bruno's philosophy influenced subsequent intellectual forces that led to the rise of modern science and to the Reformation.

Since the 15th century modern philosophy has been marked by a continuing interaction between systems of thought based on a mechanistic, materialistic interpretation of the universe and those founded on a belief in human thought as the only ultimate reality. This interaction has reflected the increasing effect of scientific discovery and political change on philosophical speculation.

 Mechanism and Materialism  
The 15th and 16th centuries constituted a period of radical social, political, and intellectual developments. The explorations of the world; the Reformation, with its emphasis on individual faith; the rise of commercial urban society; and the dramatic appearance of new ideas in all areas of culture stimulated the development of a new philosophical world view. The medieval view of the world as a hierarchical order of beings created and governed by God was supplanted by the mechanistic picture of the world as a vast machine, the parts of which move in accordance with strict physical laws, without purpose or will. The aim of human life was no longer conceived as preparation for salvation in the next world, but rather as the satisfaction of people's natural desires. Political institutions and ethical principles ceased to be regarded as reflections of divine command and came to be seen as practical devices created by humans. In this new philosophical view, experience and reason became the sole standards of truth.

The first great spokesman for the new philosophy was the English philosopher and statesman Francis Bacon, who denounced reliance on authority and verbal argument and criticized Aristotelian logic as useless for the discovery of new laws. Bacon called for a new scientific method based on inductive generalization from careful observation and experiment. He was the first to formulate rules of inductive inference.

The work of Italian physicist and astronomer Galileo was of even greater importance in the development of a new world view. Galileo brought attention to the importance of applying mathematics to the formulation of scientific laws. This he accomplished by creating the science of mechanics, which applied the principles of geometry to the motions of bodies. The success of mechanics in discovering reliable and useful laws of nature suggested to Galileo and to later scientists that all nature is designed in accordance with mechanical laws. Galileo died near Florence in 1642.

The French mathematician, physicist, and philosopher René Descartes followed Bacon and Galileo in criticizing existing methods and beliefs, but unlike Bacon, who argued for an inductive method based on observed facts, Descartes made mathematics the model for all science, applying its deductive and analytical methods to all fields. Descartes published his first major work, Essais philosophiques, in 1637. He resolved to reconstruct all human knowledge on an absolutely certain foundation by refusing to accept any belief, even the belief in his own existence, until he could prove it to be necessarily true. He found the logical proof of his own existence in the very act of doubting it, and his famous argument "Cogito, ergo sum" ("I think, therefore I am") provided him with the one certain fact or axiom from which he could deduce the existence of God and the basic laws of nature. Despite his mechanistic outlook, Descartes accepted the traditional religious doctrine of the immortality of the soul and maintained that mind and body are two distinct substances, thus exempting mind from the mechanistic laws of nature and providing for freedom of the will. His fundamental separation of mind and body, known as dualism, raised the problem of explaining the way in which two such different substances as mind and body can affect each other, a problem that he was unable to solve and that has been a concern of philosophy ever since.

 Hobbes  The English philosopher Thomas Hobbes constructed a comprehensive system of materialistic metaphysics that provided a solution to the mind-body problem by reducing mind to the internal motions of the body. Applying the principles of mechanics to all areas of knowledge, he defined the concepts basic to each area, such as life, sensation, reason, value, and justice, in terms of matter and motion, thus reducing all phenomena to physical relations and all science to mechanics. In his ethical theory Hobbes derived the rules of human behavior from the law of self-preservation and justified egoistic action as the natural human tendency. In his political theory he maintained that government and social justice are artificial creations based on social contract and maintained by force. He supported absolute monarchy as the most effective means of preserving peace. He finished De Cive, a statement of his theory of government, in 1642, and continued working as a scholar and philosopher until his death in 1679.

 Spinoza  The Dutch philosopher Baruch Spinoza constructed a remarkably precise and rigorous system of philosophy that offered new solutions to the mind-body problem, the conflict between religion and science, and the mechanistic elimination of ethical values from the natural world. Like Descartes, he maintained that the entire structure of nature can be deduced from a few basic definitions and axioms, on the model of Euclidean geometry. Spinoza saw that Descartes's theory of two substances created an insoluble problem of the way in which mind and body interact; he concluded that the only ultimate subject of knowledge must be substance itself. Attempting to demonstrate that God, substance, and nature are identical, he arrived at the pantheistic conclusion that all things are aspects or modes of God. Born and raised a Jew, Spinoza was excommunicated for his unorthodox views and banished from the city by the Amsterdam rabbis in 1656.

His solution to the mind-body problem, known as the theory of psychophysical parallelism, explained the apparent interaction of mind and body by regarding them as two forms of the same substance, which exactly parallel each other, thus seeming to affect each other but not really doing so. Spinoza's ethics, like the ethics of Hobbes, was based on a materialistic psychology according to which individuals are motivated only by self-interest, but in contrast to Hobbes, Spinoza concluded that rational self-interest coincides with the interest of others, and that the most satisfactory life is one devoted to scientific study and culminating in the intellectual love of God.

John Locke, one of the most influential figures in British thought, continued the empiricist tradition begun by Bacon. He gave empiricism a systematic framework with the publication of his Essay Concerning Human Understanding, in 1690. Locke attacked the prevalent rationalistic belief in knowledge independent of experience. Although he accepted the Cartesian (relating to Descartes) division between mind and body and the mechanistic description of nature, he redirected philosophy from study of the physical world to study of the mind. In so doing he made epistemology (the study of the nature of knowledge) the principal concern of modern philosophy. Locke attempted to reduce all ideas to simple elements of experience, but he distinguished sensation and reflection as sources of experience, sensation providing the material for knowledge of the external world, and reflection the material for knowledge of the mind.

Although not a skeptic, Locke greatly influenced the skepticism of later British thought by recognizing the vagueness of the concepts of metaphysics and by pointing out that inferences about the world outside the mind cannot be proved with certainty. His ethical and political writings had an equally great influence on subsequent thought; the founders of the modern school of utilitarianism, which makes happiness for the largest possible number of people the standard of right and wrong, drew heavily on the writings of Locke. His defense of constitutional government, religious tolerance, and natural human rights influenced the development of liberal thought in France and the United States as well as in Great Britain.

 Idealism and Skepticism  The German philosopher, mathematician, and statesman Gottfried Wilhelm Leibniz was born in Leipzig in 1646 and during his life developed a remarkably subtle and original system of philosophy. It combined the mathematical and physical discoveries of his time with the organic and religious conceptions of nature found in ancient and medieval thought. Leibniz viewed the world as an infinite number of infinitely small units of force, called monads, each of which is a closed world but mirrors all the other monads in its own system of perceptions. All the monads are spiritual entities, but those with the most confused perceptions form inanimate objects and those with the clearest perceptions, including self-consciousness and reason, constitute the souls and minds of humanity. God is conceived of as the Monad of Monads, who creates all other monads and predestines their development in accordance with a preestablished harmony that results in the appearance of interaction between the monads. Leibniz's view that all things are organic and spiritual initiated the philosophical tradition of idealism.

B1 Berkeley  
The Irish philosopher and Anglican churchman George Berkeley made idealism a powerful school in Anglo-American thought by combining it with the skepticism and empiricism that had become influential in British philosophy. Extending Locke's doubts about knowledge of the world outside the mind, Berkeley argued that no evidence exists for the existence of such a world, because the only things that one can observe are one's own sensations, and these are in the mind. To exist, he claimed, means to be perceived (esse est percipi), and in order to exist when one is not observing them, things must continue to be perceived by God. His statements of philosophy, Treatise Concerning the Principles of Human Knowledge (1710) and The Three Dialogues Between Hylas and Philonous (1713) were dismissed by his contemporaries. However, by claiming that sensory phenomena are the only objects of knowledge, Berkeley established the epistemological view of phenomenalism (a theory of perception that suggests that matter can be analyzed in terms of sensations) and prepared the way for the positivist movement in modern thought.

The Scottish philosopher and historian David Hume turned Berkeley's criticism of material substance against Berkeley's own belief in spiritual substance, arguing that no observable evidence is available for the existence of a mind substance, spirit, or God. His most important philosophical work, A Treatise of Human Nature, was published in three volumes in 1739 and 1740. All metaphysical assertions about things that cannot be directly perceived are equally meaningless, he claimed, and should be "committed to the flames." In his analyses of causality and induction, Hume revealed that no logical justification exists for believing that any two events are causally connected or for making any inference from past to future, thus raising problems that have never been solved. Hume's work has had a profound effect on modern science in stimulating the use of statistical procedures in place of deductive systems and in encouraging the redefinition of basic concepts.

In answer to the skepticism of Hume, the German philosopher Immanuel Kant constructed a comprehensive system of philosophy that ranks among the greatest intellectual achievements in Western culture. Kant combined the empiricist principle that all knowledge has its source in experience with the rationalist belief in knowledge obtained by deduction. He suggested that although the content of experience must be discovered through experience itself, the mind imposes form and order on all its experiences, and this form and order can be discovered a priori,—that is, by reflection alone. His claim that causality, substance, space, and time are forms imposed by the mind on its experience gave support to the idealism of Leibniz and Berkeley, but he made his view a more critical form of idealism by granting the empiricist claim that things-in-themselves—that is, things as they exist outside human experience—are unknowable. Kant therefore limited knowledge to the "phenomenal world" of experience, maintaining that metaphysical beliefs about the soul, the cosmos, and God (the "noumenal world" transcending human experience) are matters of faith rather than of scientific knowledge. In his ethical writings Kant held that moral principles are categorical imperatives, absolute commands of reason that permit no exceptions and are not related to pleasure or practical benefit. In his religious views, which had a lasting effect on Protestant theology, he emphasized individual conscience and represented God primarily as a moral ideal. In political and social thought Kant was a leading figure of the movement for reason and liberty against tradition and authority.

In France, intellectual activity culminated in the period known as the Enlightenment, which helped stimulate the social changes that produced the French Revolution (1789-1799). Among the leading thinkers of this period were Voltaire, who, developing the tradition of Deism begun by Locke and other liberal thinkers, reduced religious beliefs to those that can be justified by rational inference from the study of nature; Jean Jacques Rousseau, who criticized civilization as a corruption of humanity's nature and developed Hobbes's doctrine that the state is based on a social contract with its citizens and represents the popular will; and Denis Diderot, who founded the famous Encyclopédie, to which many scientists and philosophers contributed.

 Absolute Idealism  In Germany, through the influence of Kant, idealism and voluntarism (that is, emphasis on the will) became the dominant tendencies. Johann Gottlieb Fichte transformed Kant's critical idealism into absolute idealism by eliminating Kant's "things-in-themselves" and making the will the ultimate reality. Fichte maintained that the world is created by an absolute ego, of which the human will is a partial manifestation and which tends toward God as an unrealized ideal. His views were construed as atheistic and he was forced to give up the chair of philosophy at the University of Jena in 1799. Friedrich Wilhelm Joseph von Schelling went still further in reducing all things to the self-realizing activity of an absolute spirit, which he identified with the creative impulse in nature. The emphasis of romanticism on feeling and on the divinity of nature found philosophical expression in the thought of Schelling, who influenced the American transcendentalist movement, led by the poet and essayist Ralph Waldo Emerson.

C1 Hegel  
The most powerful philosophical mind of the 19th century was the German philosopher Georg Wilhelm Friedrich Hegel, whose system of absolute idealism, although influenced greatly by Kant and Schelling, was based on a new conception of logic in which conflict and contradiction are regarded as necessary elements of truth, and truth is regarded as a process rather than a fixed state of things. The source of all reality, for Hegel, is an absolute spirit, or cosmic reason, which develops from abstract, undifferentiated being into more and more concrete reality by a dialectical process consisting of triadic stages, each triad involving (1) an initial state (or thesis), (2) its opposite state (or antithesis), and (3) a higher state, or synthesis, that unites the two opposites. According to this view, history is governed by logical laws, so that "all that's real is rational, and all that's rational is real." Later historical forms are more concrete fulfillments of the absolute spirit, whose highest stage of self-realization is found in the national state and in philosophy. Hegel stimulated greater interest in history by representing it as a deeper penetration into reality than natural science. His conception of the national state as the highest social embodiment of the absolute spirit was for some time believed to be a main source of modern totalitarian ideologies, although Hegel himself argued for a large measure of individual freedom.

C2 Other Influential Philosophers  
The German philosopher Arthur Schopenhauer rejected the optimistic faith of Hegel in reason and progress. In 1819 he published The World as Will and Idea, in which he presented his atheistic and pessimistic philosophy. Schopenhauer maintained that both nature and humanity are products of an irrational will, from which people can escape only through art and through philosophical renunciation of the desire for happiness. The French mathematician and philosopher Auguste Comte formulated the philosophy of positivism, which rejected metaphysical speculation and located all genuine knowledge in the so-called positive, or factual, sciences. Comte placed the science of sociology, which he founded, at the top of his classification of the sciences. The British economist John Stuart Mill developed and refined the empiricist and utilitarian traditions, publishing Utilitarianism in 1863, and applying their principles to all fields of thought. Mill and other utilitarians influenced liberal social and economic reforms in Great Britain. The Danish religious philosopher Søren Kierkegaard attacked the Hegelian emphasis on reason, and his eloquent defense of feeling and of a subjective approach to the problems of life became one of the main sources of 20th-century existential philosophy (see Existentialism).

 Evolutionary Philosophy  The mechanistic world view of the 17th century and the faith in reason and common sense of the 18th century, although still influential, were modified in the 19th century by a variety of more complex and dynamic views, based more on biology and history than on mathematics and physics. Particularly influential was the theory of evolution through natural selection, announced in 1858 by Charles Darwin, whose work inspired conceptions of nature and of humanity that emphasized conflict and change, as against unity and substantial permanence. The German revolutionists Karl Marx and Friedrich Engels met in Paris in 1844. Together they developed the philosophy of dialectical materialism, based on the dialectical logic of Hegel, but they made matter, rather than mind, the ultimate reality. They derived from Hegel the belief that history unfolds according to dialectical laws and that social institutions are more concretely real than physical nature or individual mind. Their application of these principles to social problems took the form of historical materialism, the theory that all forms of culture are determined by economic relations and that social evolution proceeds through class conflict and periodic revolutions. This theory became the ideological basis for the Communist movement (see Communism). The British philosopher Herbert Spencer developed an evolutionary philosophy based on the principle of "the survival of the fittest," which explains all elements of nature and society as adaptations in the cosmic struggle for survival. Like Comte, he based philosophy on sociology and history, which he considered the most advanced sciences.

The German philosopher Friedrich Nietzsche returned to Schopenhauer's conception of life as the expression of a cosmic will, but he made the so-called will to power the source of all value. One of his treatises, Will to Power was published in 1901, a year after Nietzsche's death. He called for a return from religious ethics to the more primitive and natural virtues of courage and strength. Continuing the romantic revolt against reason and social organization, he stressed the values of individual self-assertion, biological instinct, and passion.

Toward the end of the 19th century, pragmatism became the most vigorous school of thought in American philosophy. It continued the empiricist tradition of grounding knowledge on experience and stressing the inductive procedures of experimental science. Charles Sanders Peirce, who gave this view its name, formulated a pragmatic theory of knowledge, which defined the meaning of a concept as the predictions that can be made by use of the concept and that can be verified by future experience. William James, whose outstanding work in psychology provided a framework for his philosophical ideas, developed the pragmatic theory of truth. He defined truth as the capacity of a belief to guide one to successful action and proposed that all beliefs be evaluated in terms of their usefulness in solving problems. James justified religion on this pragmatic basis, but, insisting on the finiteness of God, he identified God with the unconscious energy of nature.

Idealism became a powerful school of thought in Great Britain through the work of Francis Bradley, who maintained, like Hegel, that all things must be understood as aspects of an absolute totality. Bradley denied that relations exist on the ground that no two things exist and that only one real subject of thought can be postulated, the real itself. He argued that whenever a thing is said to have a certain characteristic, then this thing, as subject, must be the entire world and reality itself. Any other assumption would be self-contradictory, because anything less than reality itself has contradictory predicates; a stove, for example, is sometimes hot, but it is also sometimes cold. The Scottish philosopher John McTaggart also drew on Hegelian idealism, maintaining that space and time are unreal because their conceptions are self-contradictory. The only reality, he argued, is mind. The British philosopher Bernard Bosanquet, who, like McTaggart, revived Hegelian idealism, emphasized the aesthetic and dramatic character of the world process.

  Pragmatic Idealism  Josiah Royce, in the idealist movement in the United States, combined idealism with elements of pragmatism. Royce interpreted human life as the effort of the finite self to expand into the absolute self through science, religion, and loyalty to wider communities. His many works were published in the late 19th and early 20th centuries.

The American philosopher, educator, and psychologist John Dewey further developed the pragmatic principles of Peirce and James in a comprehensive system of thought that he called experimental naturalism, or instrumentalism. Dewey emphasized the biological and social basis of knowledge and the instrumental character of ideas as plans of action. He insisted on an experimental approach to ethics—that is, on relating values to individual and social needs. Dewey's theory of education, which stressed the preparation of the individual for creative activity in a democratic society, had a profound influence on educational methods in the United States, long after his death in 1952.

In France, the most influential view in the early part of the 20th century was the evolutionary vitalism of Henri Bergson, who propounded the élan vital, the spontaneous energy of the evolutionary process. Bergson defended feeling and intuition against the abstract, analytical approach to nature of science and science-minded philosophy. In Germany, Edmund Husserl, founder of the school of phenomenology, developed a philosophy that studied the structures of consciousness that enable the consciousness to refer to objects outside itself.

The British mathematician and philosopher Alfred North Whitehead revived interest in speculative metaphysics in the United States by developing a highly technical system of concepts that combined the Platonic theory of Ideas with the organicism of Leibniz and Bergson. Whitehead, who was also an outstanding physicist, applied the revolutionary developments in 20th-century science to show the failure of mechanistic science as a way of fully interpreting reality. According to Whitehead, things are not unchanging substances having definite spatial boundaries, but are living processes of experience embodying eternal objects, or universals, fused with them by God.

 Santayana and Others  
The American poet and philosopher George Santayana combined pragmatism, Platonism, and materialism in a comprehensive philosophy that stressed intellectual and aesthetic values. Benedetto Croce established idealism as a dominant tradition in Italian philosophy, reviving the Hegelian conception of reality as a process of historical development through the conflict of opposites, but stressing feeling and intuition, rather than abstract reason, as the source of ultimate truth. Bertrand Russell continued the empiricist and utilitarian traditions in British thought. Russell's application of developments in logic, mathematics, and physics to problems of philosophy was a major influence on the school of logical empiricism. The British philosopher G. E. Moore, the main figure in the so-called realist revolt against idealism, argued for the reality of the objects of common-sense belief. Moore's cultivated simplicity of style and highly precise use of everyday language influenced the development of the school of analytic philosophy.

 Analytic Philosophy  
The school of logical empiricism, or logical positivism, founded in Vienna, became a powerful movement in American thought. Logical empiricism, which combines the positivism of Hume and Comte with the Cartesian and Kantian concern for logical rigor and precision, rejects metaphysics as a meaningless game of words, insists on the definition of all concepts in terms of observable facts, and assigns to philosophy the task of clarifying the concepts and the logical syntax of science.

A form of analytic philosophy, also called linguistic analysis, which was inspired by the work of Moore and developed explicitly by his pupil Ludwig Wittgenstein in Tractatus Logico-philosophicus (1921; translated 1922), has become the dominant view in present-day British philosophy. This school of thought also rejects speculative metaphysics and limits philosophy to the task of clearing up intellectual puzzles caused by the ambiguity of language by analyzing the meanings of words in ordinary discourse. It identifies the meaning of a word with the way in which the word is generally used.

  Existential Philosophy  
Existential philosophy, which stems from the 19th-century romantic revolt against reason and science in favor of passionate involvement in life, became influential in Germany through the work of Martin Heidegger and Karl Jaspers. Heidegger combined the phenomenological approach of Husserl with the Kierkegaardian stress on intense emotional experience and with Hegel's conception of negation as a real force. Heidegger's philosophy substitutes Nothingness for God as the source of human values; Jaspers finds God, which he calls Transcendence, in the intense emotional experience of human beings. Jose Ortega y Gasset, the principal figure of existential philosophy in Spain, defended intuition against logic and criticized the mass culture and mechanized society of modern times. The Austrian-born Zionist author and scholar Martin Buber, combining Jewish mysticism with strains of existential thought, interpreted human experience as a dialogue between the individual and God. See also Existentialism.

Various syntheses of traditional theology with the existential view that knowledge is more emotional than scientific have been developed in Switzerland by Karl Barth and in the United States by Reinhold Niebuhr and Paul Tillich. In France, Jean-Paul Sartre fused ideas of Marx, Kierkegaard, Husserl, and Heidegger into a conception of humans as beings who project themselves out of nothingness by asserting their own values and thus assume moral responsibility for their acts.

During the 1960s the writings of the American clergyman Martin Luther King, Jr. indicated that Western philosophy had been too remote from the great social and political upheavals taking place throughout the world. Following the principles of the Indian nationalist leader Mohandas Gandhi, King advocated a program of nonviolent resistance to injustice.


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