Introduction to Philosophy

PHILOSOPHY is a study that seeks to understand the mysteries of existence and reality. It tries to discover the nature of truth and knowledge and to find what is of basic value and importance in life. It also examines the relationships between humanity and nature and between the individual and society. Philosophy arises out of wonder, curiosity, and the desire to know and understand. Philosophy is thus a form of inquiry--a process of analysis, criticism, interpretation, and speculation.

The term philosophy cannot be defined precisely because the subject is so complex and so controversial. Different philosophers have different views of the nature, methods, and range of philosophy. The term philosophy itself comes from the Greek philosophia, which means love of wisdom. In that sense, wisdom is the active use of intelligence, not something passive that a person simply possesses.

The first known Western philosophers lived in the ancient Greek world during the early 500's B.C. These early philosophers tried to discover the basic makeup of things and the nature of the world and of reality. For answers to questions about such subjects, people had largely relied on magic, superstition, religion, tradition, or authority. But the Greek philosophers considered those sources of knowledge unreliable. Instead, they sought answers by thinking and by studying nature.

Philosophy has also had a long history in some non-Western cultures, especially in China and India. But until about 200 years ago, there was little interchange between those philosophies and Western philosophy, chiefly because of difficulties of travel and communication. As a result, Western philosophy generally developed independently of Eastern philosophy.

The Importance of Philosophy

Philosophic thought is an inescapable part of human existence. Almost everyone has been puzzled from time to time by such essentially philosophic questions as "What does life mean?" "Did I have any existence before I was born?" and "Is there life after death?" Most people also have some kind of philosophy in the sense of a personal outlook on life. Even a person who claims that considering philosophic questions is a waste of time is expressing what is important, worthwhile, or valuable. A rejection of all philosophy is in itself philosophy.

By studying philosophy, people can clarify what they believe, and they can be stimulated to think about ultimate questions. A person can study philosophers of the past to discover why they thought as they did and what value their thoughts may have in one's own life. There are people who simply enjoy reading the great philosophers, especially those who were also great writers.

Philosophy has had enormous influence on our everyday lives. The very language we speak uses classifications derived from philosophy. For example, the classifications of noun and verb involve the philosophic idea that there is a difference between things and actions. If we ask what the difference is, we are starting a philosophic inquiry.

Every institution of society is based on philosophic ideas, whether that institution is the law, government, religion, the family, marriage, industry, business, or education. Philosophic differences have led to the overthrow of governments, drastic changes in laws, and the transformation of entire economic systems. Such changes have occurred because the people involved held certain beliefs about what is important, true, real, and significant and about how life should be ordered.

Systems of education follow a society's philosophic ideas about what children should be taught and for what purposes. Democratic societies stress that people learn to think and make choices for themselves. Nondemocratic societies discourage such activities and want their citizens to surrender their own interests to those of the state. The values and skills taught by the educational system of a society thus reflect the society's philosophic ideas of what is important.

The Branches of Philosophy

Philosophic inquiry can be made into any subject because philosophy deals with everything in the world and all of knowledge. But traditionally, and for purposes of study, philosophy is divided into five branches, each organized around certain distinctive questions. The branches are (1) metaphysics, (2) epistemology, (3) logic, (4) ethics, and (5) aesthetics. In addition, the philosophy of language has become so important during the 1900's that it is often considered another branch of philosophy.

Metaphysics is the study of the fundamental nature of reality and existence and of the essences of things. Metaphysics is itself often divided into two areas--ontology and cosmology. Ontology is the study of being. Cosmology is the study of the physical universe, or the cosmos, taken as a whole. Cosmology is also the name of the branch of science that studies the organization, history, and future of the universe.

Metaphysics deals with such questions as "What is real?" "What is the distinction between appearance and reality?" "What are the most general principles and concepts by which our experiences can be interpreted and understood?" and "Do we possess free will or are our actions determined by causes over which we have no control?"

Philosophers have developed a number of theories in metaphysics. These theories include materialism, idealism, mechanism, and teleology. Materialism maintains that only matter has real existence and that feelings, thoughts, and other mental phenomena are produced by the activity of matter. Idealism states that every material thing is an idea or a form of an idea. In idealism, mental phenomena are what is fundamentally important and real. Mechanism maintains that all happenings result from purely mechanical forces, not from purpose, and that it makes no sense to speak of the universe itself as having a purpose. Teleology, on the other hand, states that the universe and everything in it exists and occurs for some purpose.

Epistemology aims to determine the nature, basis, and extent of knowledge. It explores the various ways of knowing, the nature of truth, and the relationships between knowledge and belief. Epistemology asks such questions as "What are the features of genuine knowledge as distinct from what appears to be knowledge?" "What is truth, and how can we know what is true and what is false?" and "Are there different kinds of knowledge, with different grounds and characteristics?"

Philosophers often distinguish between two kinds of knowledge, a priori and empirical. We arrive at a priori knowledge by thinking, without independent appeal to experience. For example, we know that there are 60 seconds in a minute by learning the meanings of the terms. In the same way, we know that there are 60 minutes in an hour. From these facts, we can deduce that there are 3,600 seconds in an hour, and we arrive at this conclusion by the operation of thought alone. We acquire empirical knowledge from observation and experience. For example, we know from observation how many keys are on a typewriter and from experience which key will print what letter.

The nature of truth has baffled people since ancient times, partly because people so often use the term true for ideas they find congenial and want to believe, and also because people so often disagree about which ideas are true. Philosophers have attempted to define criteria for distinguishing between truth and error. But they disagree about what truth means and how to arrive at true ideas. The correspondence theory holds that an idea is true if it corresponds to the facts or reality. The pragmatic theory maintains that an idea is true if it works or settles the problem it deals with. The coherence theory states that truth is a matter of degree and that an idea is true to the extent to which it coheres (fits together) with other ideas that one holds. Skepticism claims that knowledge is impossible to attain and that truth is unknowable.

Logic is the study of the principles and methods of reasoning. It explores how we distinguish between good (or sound) reasoning and bad (or unsound) reasoning. An instance of reasoning is called an argument or an inference. An argument consists of a set of statements called premises together with a statement called the conclusion, which is supposed to be supported by or derived from the premises. A good argument provides support for its conclusion, and a bad argument does not. Two basic types of reasoning are called deductive and inductive.

A good deductive argument is said to be valid--that is, the conclusion necessarily follows from the premises. A deductive argument whose conclusion does not follow necessarily from the premises is said to be invalid. The argument "All human beings are mortal, all Greeks are human beings, therefore all Greeks are mortal" is a valid deductive argument. But the argument "All human beings are mortal, all Greeks are mortal, therefore all Greeks are human beings" is invalid, even though the conclusion is true. On that line of reasoning, one could argue that all dogs, which are also mortal, are human beings.

Deductive reasoning is used to explore the necessary consequences of certain assumptions. Inductive reasoning is used to establish matters of fact and the laws of nature and does not aim at being deductively valid. One who reasons that all squirrels like nuts, on the basis that all squirrels so far observed like nuts, is reasoning inductively. The conclusion could be false, even though the premise is true. Nevertheless, the premise provides considerable support for the conclusion.

Ethics concerns human conduct, character, and values. It studies the nature of right and wrong and the distinction between good and evil. Ethics explores the nature of justice and of a just society, and also one's obligations to oneself, to others, and to society.

Ethics asks such questions as "What makes right actions right and wrong actions wrong?" "What is good and what is bad?" and "What are the proper values of life?" Problems arise in ethics because we often have difficulty knowing exactly what is the right thing to do. In many cases, our obligations conflict or are vague. In addition, people often disagree about whether a particular action or principle is morally right or wrong.

A view called relativism maintains that what is right or wrong depends on the particular culture concerned. What is right in one society may be wrong in another, this view argues, and so no basic standards exist by which a culture may be judged right or wrong. Objectivism claims that there are objective standards of right and wrong which can be discovered and which apply to everyone. Subjectivism states that all moral standards are subjective matters of taste or opinion.

Aesthetics deals with the creation and principles of art and beauty. It also studies our thoughts, feelings, and attitudes when we see, hear, or read something beautiful. Something beautiful may be a work of art, such as a painting, symphony, or poem, or it may be a sunset or other natural phenomenon. In addition, aesthetics investigates the experience of engaging in such activities as painting, dancing, acting, and playing.

Aesthetics is sometimes identified with the philosophy of art, which deals with the nature of art, the process of artistic creation, the nature of the aesthetic experience, and the principles of criticism. But aesthetics has wider application. It involves both works of art created by human beings and the beauty found in nature.

Aesthetics relates to ethics and political philosophy when we ask questions about what role art and beauty should play in society and in the life of the individual. Such questions include "How can people's taste in the arts be improved?" "How should the arts be taught in the schools?" and "Do governments have the right to restrict artistic expression?"

The Philosophy of Language has become especially important in recent times. Some philosophers claim that all philosophic questions arise out of linguistic problems. Others claim that all philosophic questions are really questions about language. One key question is "What is language?" But there are also questions about the relationships between language and thought and between language and the world, as well as questions about the nature of meaning and of definition.

The question has been raised whether there can be a logically perfect language that would reflect in its categories the essential characteristics of the world. This question raises questions about the adequacy of ordinary language as a philosophic tool. All such questions belong to the philosophy of language, which has essential connections with other branches of philosophy.

Philosophy and Other Fields

One peculiarity of philosophy is that the question "What is philosophy?" is itself a question of philosophy. But the question "What is art?" is not a question of art. The question is philosophic. The same is true of such questions as "What is history?" and "What is law?" Each is a question of philosophy. Such questions are basic to the philosophy of education, the philosophy of history, the philosophy of law, and other "philosophy of" fields. Each of these fields attempts to determine the foundations, fundamental categories, and methods of a particular institution or area of study. A strong relationship therefore exists between philosophy and other fields of human activity. This relationship can be seen by examining two fields: (1) philosophy and science and (2) philosophy and religion.

Philosophy and Science. Science studies natural phenomena and the phenomena of society. It does not study itself. When science does reflect on itself, it becomes the philosophy of science and examines a number of philosophic questions. These questions include "What is science?" "What is scientific method?" "Does scientific truth provide us with the truth about the universe and reality?" and "What is the value of science?"

Philosophy has given birth to several major fields of scientific study. Until the 1700's, no distinction was made between science and philosophy. For example, physics was called natural philosophy. Psychology was part of what was called moral philosophy. In the early 1800's, sociology and linguistics separated from philosophy and became distinct areas of study. Logic has always been considered a branch of philosophy. However, logic has now developed to the point where it is also a branch of mathematics, which is a basic science.

Philosophy and science differ in many respects. For example, science has attained definite and tested knowledge of many matters and has thus resolved disagreement about those matters. Philosophy has not. As a result, controversy has always been characteristic of philosophy. Science and philosophy do share one significant goal. Both seek to discover the truth--to answer questions, solve problems, and satisfy curiosity. In the process, both science and philosophy provoke further questions and problems, with each solution bringing more questions and problems.

Philosophy and Religion. Historically, philosophy originated in religious questions. These questions concerned the nature and purpose of life and death and the relationship of humanity to superhuman powers or a divine creator. Every society has some form of religion. Most people acquire their religion from their society as they acquire their language. Philosophy inquires into the essence of things, and inquiry into the essence of religion is a philosophic inquiry.

Religious ideas generated some of the earliest philosophic speculations about the nature of life and the universe. The speculations often centered on the idea of a supernatural or superpowerful being who created the universe and who governs it according to unchangeable laws and gives it purpose. Western philosophic tradition has paid much attention to the possibility of demonstrating the existence of God.

The chief goal of some philosophers is not understanding and knowledge. Instead, they try to help people endure the pain, anxiety, and suffering of earthly existence. Such philosophers attempt to make philosophic reflection on the nature and purpose of life perform the function of religion.

Oriental Philosophy

There are two main traditions in Oriental philosophy, Chinese and Indian. Both philosophies are basically religious and ethical in origin and character. They are removed from any interest in science.

Traditionally, Chinese philosophy has been largely practical, humanistic, and social in its aims. It developed as a means of bringing about improvements in society and politics. Traditionally, philosophy in India has been chiefly mystical rather than political. It has been dominated by reliance on certain sacred texts, called Vedas, which are considered inspired and true and therefore subject only for commentary and not for criticism. Much of Indian philosophy has emphasized withdrawal from everyday life into the life of the spirit. Chinese philosophy typically called for efforts to participate in the life of the state in order to improve worldly conditions.

Chinese philosophy as we know it started in the 500's B.C. with the philosopher Confucius. His philosophy, called Confucianism, was the official philosophy of China for centuries, though it was reinterpreted by different generations. Confucianism aimed to help people live better and more rewarding lives by discipline and by instruction in the proper goals of life. Candidates for government positions had to pass examinations on Confucian thought, and Confucianism formed the basis for government decisions. No other civilization has placed such emphasis on philosophy.

Other philosophic traditions in China were Taoism, Mohism, and realism. Beginning in the 1100's, a movement known as Neo-Confucianism incorporated elements of all these doctrines.

We do not know exactly when Indian philosophy began. In India, philosophic thought was intermingled with religion, and most Indian philosophic thought has been religious in character and aim. Philosophic commentaries on sacred texts emerge during the 500's B.C. The Indian word for these studies is darshana, which means vision or seeing. It corresponds to what the ancient Greeks called philosophia.

In India, as in China, people conceived of philosophy as a way of life, not as a mere intellectual activity. The main aim of Indian philosophy was freedom from the suffering and tension caused by the body and the senses and by attachment to worldly things. The main philosophies developed in India were Hinduism and Buddhism, which were also religions. Yet some Indian philosophers did develop a complex system of logic and carried on investigations in epistemology. Some Indian philosophic ideas have been influential in the West. One such idea is reincarnation, the belief that the human soul is successively reborn in new bodies.

The History of Western Philosophy

The history of Western philosophy is commonly divided into three periods--ancient, medieval, and modern. The period of ancient philosophy extended from about 600 B.C. to about the A.D. 400's. Medieval philosophy lasted from the 400's to the 1600's. Modern philosophy covers the period from the 1600's to the present.

Ancient Philosophy was almost entirely Greek. The greatest philosophers of the ancient world were three Greeks of the 400's and 300's B.C.--Socrates, Plato, and Aristotle. Their philosophy influenced all later Western culture. Our ideas in the fields of metaphysics, science, logic, and ethics originated from their thought. A number of distinctive schools of philosophy also flourished in ancient Greece.

The Pre-Socratics were the first Greek philosophers. Their name comes from the fact that most of them lived before the birth of Socrates, which was about 469 B.C. The pre-Socratic philosophers were mainly interested in the nature and source of the universe and the nature of reality. They wanted to identify the fundamental substance that they thought underlay all phenomena, and in terms of which all phenomena could be explained.

Unlike most other people of their time, the pre-Socratic philosophers did not believe that gods or supernatural forces caused natural events. Instead, they sought a natural explanation for natural phenomena. The philosophers saw the universe as a set of connected and unified phenomena for which thought could find an explanation. They gave many different and conflicting answers to basic philosophic questions. However, the importance of the pre-Socratics lies not in the truth of their answers but in the fact that they examined the questions in the first place. They had no philosophic tradition to work from, but their ideas provided a tradition for all later philosophers.

Socrates left no writings, though he was constantly engaged in philosophic discussion. Our knowledge of his ideas and methods comes mainly from dialogues written by his pupil Plato. In most of the dialogues, Socrates appears as the main character, who leads and develops the process of inquiry.

Socrates lived in Athens and taught in the streets, market place, and gymnasiums. He taught by a question-and-answer method. Socrates tried to get a definition or precise view of some abstract idea, such as knowledge, virtue, justice, or wisdom. He would use close, sharp questioning, constantly asking "What do you mean?" and "How do you know?" This procedure, called the Socratic method, became the model for philosophic methods that emphasize debate and discussion.

Socrates wanted to replace vague opinions with clear ideas. He often questioned important Athenians and exposed their empty claims to knowledge and wisdom. This practice made him many enemies, and he was put to death as a danger to the state. He thus became a symbol of the philosopher who pursued an argument wherever it led to arrive at the truth, no matter what the cost.

Plato believed that we cannot gain knowledge of things through our senses because the objects of sense perception are fleeting and constantly changing. Plato stated that we can have genuine knowledge only of changeless things, such as truth, beauty, and goodness, which are known by the mind. He called such things ideas or forms.

Plato taught that only ideas are real and that all other things only reflect ideas. This view became known as idealism. According to Plato, the most important idea is the idea of good. Knowledge of good is the object of all inquiry, a goal to which all other things are subordinate. Plato stated that the best life is one of contemplation of eternal truths. However, he believed people who have attained this state must return to the world of everyday life and use their skills and knowledge to serve humanity. Plato also believed that the soul is immortal and that only the body perishes at death. His ideas contributed to views about the body, soul, and eternal things later developed in Christian theology.

Aristotle, Plato's greatest pupil, wrote about almost every known subject of his day. He invented the idea of a science and of separate sciences, each having distinct principles and dealing with different subject matter. He wrote on such topics as physics, astronomy, psychology, biology, physiology, and anatomy. Aristotle also investigated what he called "first philosophy," later known as metaphysics.

Aristotle created the earliest philosophic system. In his philosophy, all branches of inquiry and knowledge are parts of some overall system and connected by the same concepts and principles. Aristotle believed that all things in nature have some purpose. According to his philosophy, the nature of each thing is determined by its purpose, and all things seek to fulfill their natures by carrying out these purposes.

Aristotle's basic method of inquiry consisted of starting from what we know or think we know and then asking how, what, and why. In his metaphysics, he developed the idea of a first cause, which was not itself caused by anything, as the ultimate explanation of existence. Christian theologians later adopted this idea as a basic argument for the existence of God. Aristotle taught that everyone aims at some good. He said that happiness does not lie in pleasure but in virtuous activity. By virtuous activity, he meant behaving according to a mean between extremes. For example, courage is the mean between the extremes of cowardice and foolhardiness. The highest happiness of all, Aristotle believed, was the contemplative use of the mind.

Stoic Philosophy and Epicureanism were the two main schools of Greek philosophy that emerged after the death of Aristotle in 322 B.C. Both schools taught that the purpose of knowing is to enable a person to lead the best and most contented life.

Stoic philosophy was founded by Zeno of Citium. He taught that people should spend their lives trying to cultivate virtue, the greatest good. The Stoics believed in strict determinism--the idea that all things are fated to be. Therefore, they said, a wise and virtuous person accepts and makes the best of what cannot be changed. Stoicism spread to Rome. There, the chief Stoics included the statesman Marcus Tullius Cicero, the emperor Marcus Aurelius, and the teacher Epictetus.

Epicureanism was founded by Epicurus. Epicurus based his philosophy on hedonism--the idea that the only good in life is pleasure. However, Epicurus taught that not all pleasures are good. The only good pleasures are calm and moderate ones because extreme pleasures could lead to pain. The highest pleasures, Epicurus said, are physical health and peace of mind, two kinds of freedom from pain.

Skepticism was a school of philosophy founded by Pyrrho of Elis about the same time that Stoic philosophy and Epicureanism flourished. Pyrrho taught that we can know nothing. Our senses, he said, deceive us and provide no accurate knowledge of the way things are. Thus, all claims to knowledge are false. Because we can know nothing, in this view, we should treat all things with indifference and make no judgments.

Neoplatonism was a revived version of some of Plato's ideas as adapted by Plotinus, a philosopher who may have been born in Egypt in the A.D. 200's. Neoplatonism tried to guide the individual toward a unity--a oneness--with God, which is a state of blessedness. Plotinus believed that the human soul yearns for reunion with God, which it can achieve only in mystical experience. Neoplatonism provided the bridge between Greek philosophy and early Christian philosophy. It inspired the idea that important truths can be learned only through faith and God's influence, not by reason.

Medieval Philosophy. During the Middle Ages, Western philosophy developed more as a part of Christian theology than as an independent branch of inquiry. The philosophy of Greece and Rome survived only in its influence on religious thought.

Saint Augustine was the greatest philosopher of the early Middle Ages. In a book titled The City of God (early 400's), Augustine interpreted human history as a conflict between faithful Christians living in the city of God and pagans and heretics living in the city of the world. Augustine wrote that the people of the city of God will gain eternal salvation, but the people in the city of the world will receive eternal punishment. The book weakened the belief in the pagan religion of Rome and helped further the spread of Christianity.

A system of thought called scholasticism dominated medieval philosophy from about the 1100's to the 1400's. The term scholasticism refers to the method of philosophic investigation used by teachers of philosophy and theology in the newly developing universities of western Europe. The teachers were called scholastics. The scholastic method consisted in precise analysis of concepts with subtle distinctions between different senses of these concepts. The scholastics used deductive reasoning from principles established by their method to provide solutions to problems.

Scholasticism was basically generated by the translation of Aristotle's works into Latin, the language of the medieval Christian church. These works presented medieval thinkers with the problem of reconciling Aristotle's great body of philosophic thought with the Bible and Christian doctrine. The most famous scholastic was Saint Thomas Aquinas. His philosophy combined Aristotle's thought with theology, and it eventually became the official philosophy of the Roman Catholic Church.

The great contributions of the scholastics to philosophy included major development of the philosophy of language. The scholastics studied how features of language can affect our understanding of the world. They also emphasized the importance of logic to philosophic inquiry.

Modern Philosophy. A great cultural movement in Europe called the Renaissance overlapped the end of the Middle Ages and formed a transition between medieval and modern philosophy. The Renaissance began in Italy and lasted from about 1300 to about 1600. It was a time of intellectual reawakening stemming from the rediscovery of ancient Greek and Roman culture. During the Renaissance, major advances occurred in such sciences as astronomy, physics, and mathematics. Scholars called humanists stressed the importance of human beings and the study of classical literature as a guide to understanding life. Emphasis on science and on humanism led to changes in the aims and techniques of philosophic inquiry. Scholasticism declined, and philosophy was freed of its ties to medieval theology.

One of the earliest philosophers to support the scientific method was Francis Bacon of England. Most historians consider Bacon and Rene Descartes of France to be the founders of modern philosophy. Bacon wrote two influential works, The Advancement of Learning (1605) and Novum Organum (1620). He stated that knowledge was power and that knowledge could be obtained only by the inductive method of investigation. Bacon imagined a new world of culture and leisure that could be gained by inquiry into the laws and processes of nature. In describing this world, he anticipated the effects of advances in science, engineering, and technology.

Rationalism was a philosophic outlook that arose in the 1600's. The basic idea of rationalism is that reason is superior to experience as a source of knowledge and that the validity of sense perception must be proved from more certain principles. The rationalists tried to determine the nature of the world and of reality by deduction from premises themselves established as certain a priori. They also stressed the importance of mathematical procedures. The leading rationalists were Rene Descartes, Baruch Spinoza, and Gottfried Leibniz.

Descartes was a mathematician as well as a philosopher. He invented analytic geometry. Descartes's basic idea was to establish a secure foundation for the sciences, a foundation of the sort he had found for mathematics. He was thus much concerned with the foundations of knowledge, and he started philosophy on its persistent consideration of epistemological problems. Descartes was a mechanist--that is, he regarded all physical phenomena as connected mechanically by laws of cause and effect. Descartes's philosophy generated the problem of how mind and matter are related.

Spinoza constructed a system of philosophy on the model of geometry. He attempted to derive philosophic conclusions from a few central axioms (supposedly self-evident truths) and definitions. Spinoza did not view God as some superhuman being who created the universe. He identified God with the universe. Spinoza was also a mechanist, regarding everything in the universe as determined. Spinoza's main aim was ethical. He wanted to show how people could be free, could lead reasonable and thus satisfying lives, in a deterministic world.

Leibniz believed that the actual world is only one of many possible worlds. He tried to show how the actual world is the best of all possible worlds in an effort to justify the ways of God to humanity. Thus, he attempted to solve the problem of how a perfect and all-powerful God could have created a world filled with so much suffering and evil. Leibniz and Sir Isaac Newton, an English scientist, independently developed calculus. Leibniz' work in mathematics anticipated the development of symbolic logic--the use of mathematical symbols and operations to solve problems in logic.

Empiricism emphasizes the importance of experience and sense perception as the source and basis of knowledge. The first great empiricist was John Locke of England in the 1600's. George Berkeley of Ireland and David Hume of Scotland further developed empiricism in the 1700's.

Locke tried to determine the origin, extent, and certainty of human knowledge in An Essay Concerning Human Understanding (1690). Locke argued that there are no innate ideas--that is, ideas people are born with. He believed that when a person is born, the mind is like a blank piece of paper. Experience is therefore the source of all ideas and all knowledge.

Berkeley dealt with the question "If whatever a human being knows is only an idea, how can one be sure that there is anything in the world corresponding to that idea?" Berkeley answered that "to be is to be perceived." No object exists, he said, unless it is perceived by some mind. Material objects are ideas in the mind and have no independent existence.

Hume extended the theories of Locke and Berkeley to a consistent skepticism about almost everything. He maintained that everything in the mind consists of impressions and ideas, with ideas coming from impressions. Every idea can be traced to and tested by some earlier impression. According to Hume, we must be able to determine from what impression we derived an idea for that idea to have meaning. An apparent idea that cannot be traced to an impression must be meaningless. Hume also raised the question of how can we know that the future will be like the past--that the laws of nature will continue to operate as they have. He claimed that we can only know that events have followed certain patterns in the past. We cannot therefore be certain that events will continue to follow those patterns.

The Age of Reason was a period of great intellectual activity that began in the 1600's and lasted until the late 1700's. The period is also called the Enlightenment. Philosophers of the Age of Reason stressed the use of reason, as opposed to the reliance on authority and scriptural revelation. For them, reason provided means of attaining the truth about the world and of ordering human society to assure human well-being. The leading philosophers included Descartes, Locke, Berkeley, and Hume. They also included Jean Jacques Rousseau, Voltaire, Denis Diderot, and other members of a group of French philosophers called the philosophes.

Locke's philosophic ideas were characteristic of the Age of Reason. Locke sought to determine the limits of human understanding and to discover what can be known within those limits that will serve as a guide to life and conduct. He tried to show that people should live by the principles of toleration, liberty, and natural rights. His Two Treatises of Government (1690) provided the philosophic base for the Revolutionary War in America and the French Revolution in the late 1700's.

The Philosophy of Immanuel Kant, a great German philosopher of the late 1700's, became the foundation for nearly all later developments in philosophy. Kant's philosophy is called critical philosophy or transcendental philosophy. Kant was stimulated by the skeptical philosophy of Hume to try to bring about a synthesis of rationalism and empiricism. In his Critique of Pure Reason (1781), Kant tried to provide a critical account of the powers and limits of human reason, to determine what is knowable and what is unknowable. Kant concluded that reason can provide knowledge only of things as they appear to us, never of things as they are in themselves. Kant believed that the mind plays an active role in knowing and is not a mere recorder of facts presented by the senses. The mind does this through basic categories or forms of understanding, which are independent of experience and without which our experience would not make sense. Through such categories and the operations of the mind, working on sense experience, we can have knowledge, but only of things that can be experienced.

Kant criticized the traditional arguments for the existence of God. He argued that they are all in error because they make claims that go beyond the possibility of experience and thus go beyond the powers of human reason. In his Critique of Practical Reason (1788), Kant argued that practical reason (reason applied to practice) can show us how we ought to act and also provides a practical reason for believing in God, though not a proof that God exists.

Philosophy in the 1800's. Kant's philosophy stimulated various systems of thought in the 1800's, such as those of G. W. F. Hegel and Karl Marx of Germany. Hegel developed a theory of historical change called dialectic, in which the conflict of opposites results in the creation of a new unity and then its opposite. Hegel's theory was transformed by Marx into dialectical materialism. Marx believed that only material things are real. He stated that all ideas are built on an economic base. He believed that the dialectic of conflict between capitalists and industrial workers will lead to the establishment of communism, which he called socialism, as an economic and political system.

Friedrich Nietzsche, a German philosopher, was an atheist who proclaimed in Thus Spake Zarathustra (1883-1885) that "God is dead." Nietzsche meant that the idea of God had lost the power to motivate and discipline large masses of people. He believed that people would have to look to some other idea to guide their lives. Nietzsche predicted the evolution of the superman, who would be beyond the weakness of human beings and beyond the merely human appeals to morality. He regarded such appeals as appeals to weakness, not strength. He felt that all behavior is based on the will to power--the desire of people to control others and their own passions. The superman would develop a new kind of perfection and excellence through the capacity to realize the will to power through strength, rather than weakness.

The dominant philosophy in England during the 1800's was utilitarianism, developed by Jeremy Bentham and John Stuart Mill. The utilitarians maintained that the greatest happiness for the greatest number of people is the test of right and wrong. They argued that all existing social institutions, especially law and government, must be transformed to satisfy the test of greatest happiness. In The Subjection of Women (1869), Mill wrote that the legal subordination of women to men ought to be replaced by "a principle of perfect equality." That idea was revolutionary in Mill's time.

Philosophy in the 1900's has seen five main movements predominate. Two of these movements, existentialism and phenomenology, have had their greatest influence in the countries on the mainland of western Europe. The three other movements, pragmatism, logical positivism, and philosophical analysis, have been influential chiefly in the United States and Great Britain.

Existentialism became influential in the mid-1900's. World War II (1939-1945) gave rise to widespread feelings of despair and of separation from the established order. These feelings led to the idea that people have to create their own values in a world in which traditional values no longer govern. Existentialism insists that choices have to be made arbitrarily by individuals, who thus create themselves, because there are no objective standards to determine choice. The most famous of the existentialist philosophers is the French author Jean-Paul Sartre.

Phenomenology was developed by the German philosopher Edmund Husserl. Husserl conceived the task of phenomenology, hence the task of philosophy, as describing phenomena--the objects of experience--accurately and independently of all assumptions derived from science. He thought that this activity would provide philosophic knowledge of reality.

Pragmatism, represented in the 1900's by William James and John Dewey of the United States, maintains knowledge is subordinate to action. The meaning and truth of ideas are determined by their relation to practice.

Logical positivism, developed in Vienna, Austria, in the 1920's, believes philosophy should analyze the logic of the language of science. It regards science as the only source of knowledge and claims metaphysics is meaningless. It bases this claim on the principle of verifiability, by which a statement is meaningful only if it can be verified by sense experience.

Philosophical analysis generally tries to solve philosophic problems through analysis of language or concepts. Some versions of this philosophy attempt to show that traditional philosophic problems dissolve--that is, disappear--on proper analysis of the terms in which they are expressed. Other versions use linguistic analysis to throw light on, not dissolve, traditional philosophic problems. The most influential philosophers practicing philosophic analysis have been Bertrand Russell of England and Ludwig Wittgenstein, who was born in Austria but studied and taught in England.