Philosophy



Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. It is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational argument. The word "philosophy" comes from the Greek φιλοσοφία (philosophia), which literally means "love of wisdom".

Branches of philosophy
The following branches are the main areas of study:


 * Metaphysics is the study of the nature of reality, including the relationship between mind and body, substance and accident, events and causation. Traditional branches are cosmology and ontology.
 * Epistemology is concerned with the nature and scope of knowledge, and whether knowledge is possible. Among its central concerns has been the challenge posed by skepticism and the relationships between truth, belief, and justification.
 * Ethics, or "moral philosophy", is concerned primarily with the question of the best way to live, and secondarily, concerning the question of whether this question can be answered. The main branches of ethics are meta-ethics, normative ethics, and applied ethics. Meta-ethics concerns the nature of ethical thought, such as the origins of the words good and bad, and origins of other comparative words of various ethical systems, whether there are absolute ethical truths, and how such truths could be known. Normative ethics are more concerned with the questions of how one ought to act, and what the right course of action is.  This is where most ethical theories are generated.  Lastly, applied ethics go beyond theory and step into real world ethical practice, such as questions of whether or not abortion is correct. Ethics is also associated with the idea of morality, and the two are often interchangeable.
 * Political philosophy is the study of government and the relationship of individuals (or families and clans) to communities including the state. It includes questions about justice, law, property, and the rights and obligations of the citizen. Politics and ethics are traditionally inter-linked subjects, as both discuss the question of what is good and how people should live.
 * Aesthetics deals with beauty, art, enjoyment, sensory-emotional values, perception, and matters of taste and sentiment.
 * Logic is the study of valid argument forms. Beginning in the late 19th century, mathematicians such as Gottlob Frege focused on a mathematical treatment of logic, and today the subject of logic has two broad divisions: mathematical logic (formal symbolic logic) and what is now called philosophical logic.

Other major fields within philosophy include


 * Philosophy of language is inquiry into the nature, origins, and usage of language.
 * Philosophy of law (more commonly called Jurisprudence) is inquiry into the varying theories explaining the nature, and interpretations of the law in society.
 * Philosophy of mind deals with the nature of the mind and its relationship to the body, and is typified by disputes between dualism and materialism. In recent years there has been increasing similarity between this branch of philosophy and cognitive science.
 * Philosophy of religion is a branch of philosophy that asks questions about religion.
 * Philosophy of science is a branch of philosophy that asks questions about science.

Many academic subjects have a philosophy, for example, the philosophy of mathematics, the philosophy of logic, the philosophy of law, and the philosophy of history. In addition, a range of academic subjects have emerged to deal with areas that historically were the subject of philosophy. These include physics, anthropology, and psychology.

Western philosophy
The introduction of the terms "philosopher" and "philosophy" has been ascribed to the Greek thinker Pythagoras. The ascription is said to be based on a passage in a lost work of Herakleides Pontikos, a disciple of Aristotle. It is considered to be part of the widespread body of legends of Pythagoras of this time. "Philosopher" was understood as a word which contrasted with "sophist" (from sophoi). Traveling sophists or "wise men" were important in Classical Greece, often earning money as teachers, whereas philosophers are "lovers of wisdom" and not professionals.

Historians of western philosophy usually divide the subject into three or more periods, the most important being ancient philosophy, medieval philosophy, and modern philosophy.

Ancient philosophy (c. 600 BC–c. AD 400)
Ancient philosophy is the philosophy of the Graeco-Roman world from the 6th century [c. 585] BC to the 6th century AD. It is usually divided into three periods: the pre-Socratic period, the period of Plato and Aristotle, and the post-Aristotelian (or Hellenistic) period. A fourth period that is sometimes added includes the Neoplatonic and Christian philosophers of Late Antiquity. The most important of the ancient philosophers (in terms of subsequent influence) are Plato and Aristotle.

The main subjects of ancient philosophy are: understanding the fundamental causes and principles of the universe; explaining it in an economical way; the epistemological problem of reconciling the diversity and change of the natural universe, with the possibility of obtaining fixed and certain knowledge about it; questions about things that cannot be perceived by the senses, such as numbers, elements, universals, and gods. Socrates is said to have been the initiator of more focused study upon the human things including the analysis of patterns of reasoning and argument and the nature of the good life and the importance of understanding and knowledge in order to pursue it; the explication of the concept of justice, and its relation to various political systems.

In this period the crucial features of the philosophical method were established: a critical approach to received or established views, and the appeal to reason and argumentation.

Medieval philosophy (c. 400–c. 1350)
Medieval philosophy is the philosophy of Western Europe and the Middle East during the Middle Ages, roughly extending from the Christianization of the Roman Empire until the Renaissance. Medieval philosophy is defined partly by the rediscovery and further development of classical Greek and Hellenistic philosophy, and partly by the need to address theological problems and to integrate the then widespread sacred doctrines of Abrahamic religion (Islam, Judaism, and Christianity) with secular learning.

The history of western European medieval philosophy is traditionally divided into two main periods: the period in the Latin West following the Early Middle Ages until the 12th century, when the works of Aristotle and Plato were preserved and cultivated; and the "golden age" of the 12th, 13th and 14th centuries in the Latin West, which witnessed the culmination of the recovery of ancient philosophy, and significant developments in the field of philosophy of religion, logic and metaphysics.

The medieval era was disparagingly treated by the Renaissance humanists, who saw it as a barbaric "middle" period between the classical age of Greek and Roman culture, and the "rebirth" or renaissance of classical culture. Yet this period of nearly a thousand years was the longest period of philosophical development in Europe, and possibly the richest. Jorge Gracia has argued that "in intensity, sophistication, and achievement, the philosophical flowering in the thirteenth century could be rightly said to rival the golden age of Greek philosophy in the fourth century B.C."

Some problems discussed throughout this period are the relation of faith to reason, the existence and unity of God, the object of theology and metaphysics, the problems of knowledge, of universals, and of individuation.

Philosophers from the Middle Ages include the Christian philosophers Augustine of Hippo, Boethius, Anselm, Gilbert of Poitiers, Peter Abelard, Roger Bacon, Bonaventure, Thomas Aquinas, Duns Scotus, William of Ockham and Jean Buridan; the Jewish philosophers Maimonides and Gersonides; and the Muslim philosophers Alkindus, Alfarabi, Alhazen, Avicenna, Algazel, Avempace, Abubacer and Averroes. The medieval tradition of Scholasticism continued to flourish as late as the 17th century, in figures such as Francisco Suarez and John of St. Thomas.

Aquinas, father of Thomism, was immensely influential in Catholic Europe, placed a great emphasis on reason and argumentation, and was one of the first to use the new translation of Aristotle's metaphysical and epistemological writing. His work was a significant departure from the Neoplatonic and Augustinian thinking that had dominated much of early Scholasticism.

Renaissance philosophy (c. 1350–c. 1600)
The Renaissance ("rebirth") was a period of transition between the Middle Ages and modern thought, in which the recovery of classical texts helped shift philosophical interests away from technical studies in logic, metaphysics, and theology towards eclectic inquiries into morality, philology, and mysticism. The study of the classics and the humane arts generally, such as history and literature, enjoyed a scholarly interest hitherto unknown in Christendom, a tendency referred to as humanism. Displacing the medieval interest in metaphysics and logic, the humanists followed Petrarch in making man and his virtues the focus of philosophy.

The study of classical philosophy also developed in two new ways. On the one hand, the study of Aristotle was changed through the influence of Averroism. The disagreements between these Averroist Aristotelians, and more orthodox catholic Aristotelians such as Albertus Magnus and Thomas Aquinas eventually contributed to the development of a "humanist Aristotelianism" developed in the Renaissance, as exemplified in the thought of Pietro Pomponazzi and Giacomo Zabarella. Secondly, as an alternative to Aristotle, the study of Plato and the Neoplatonists became common. This was assisted by the rediscovery of works which had not been well known previously in Western Europe. Notable Renaissance Platonists include Nicholas of Cusa, and later Marsilio Ficino and Giovanni Pico della Mirandola.

The Renaissance also renewed interest in anti-Aristotelian theories of nature considered as an organic, living whole comprehensible independently of theology, as in the work of Nicholas of Cusa, Nicholas Copernicus, Giordano Bruno, Telesius, and Tommaso Campanella. Such movements in natural philosophy dovetailed with a revival of interest in occultism, magic, hermeticism, and astrology, which were thought to yield hidden ways of knowing and mastering nature (e.g., in Marsilio Ficino and Giovanni Pico della Mirandola).

These new movements in philosophy developed contemporaneously with larger religious and political transformations in Europe: the Reformation and the decline of feudalism. Though the theologians of the Protestant Reformation showed little direct interest in philosophy, their destruction of the traditional foundations of theological and intellectual authority harmonized with a revival of fideism and skepticism in thinkers such as Erasmus, Montaigne, and Francisco Sanches. Meanwhile, the gradual centralization of political power in nation-states was echoed by the emergence of secular political philosophies, as in the works of Niccolò Machiavelli (often described as the first modern political thinker, or a key turning point towards modern political thinking ), Thomas More, Erasmus, Justus Lipsius, Jean Bodin, and Hugo Grotius.

Early modern philosophy (c. 1600–c. 1800)


Chronologically, the early modern era of western philosophy is usually identified with the 17th and 18th centuries, with the 18th century often being referred to as the Enlightenment. Modern philosophy is distinguished from its predecessors by its increasing independence from traditional authorities such as the Church, academia, and Aristotelianism; a new focus on the foundations of knowledge and metaphysical system-building;  and the emergence of modern physics out of natural philosophy. Other central topics of philosophy in this period include the nature of the mind and its relation to the body, the implications of the new natural sciences for traditional theological topics such as free will and God, and the emergence of a secular basis for moral and political philosophy. These trends first distinctively coalesce in Francis Bacon's call for a new, empirical program for expanding knowledge, and soon found massively influential form in the mechanical physics and rationalist metaphysics of Rene Descartes. Thomas Hobbes was the first to apply this methodology systematically to political philosophy and is the originator of modern political philosophy, including the modern theory of a "social contract". The academic canon of early modern philosophy generally includes Descartes, Spinoza, Leibniz, Locke, Berkeley, Hume, and Kant,  though influential contributions to philosophy were made by many thinkers in this period, such as Galileo Galilei, Pierre Gassendi, Blaise Pascal, Nicolas Malebranche, Isaac Newton, Christian Wolff, Montesquieu, Pierre Bayle, Thomas Reid, Jean d'Alembert, and Adam Smith. Jean-Jacques Rousseau was a seminal figure in initiating reaction against the Enlightenment. The approximate end of the early modern period is most often identified with Immanuel Kant's systematic attempt to limit metaphysics, justify scientific knowledge, and reconcile both of these with morality and freedom.

19th-century philosophy
Later modern philosophy is usually considered to begin after the philosophy of Immanuel Kant at the beginning of the 19th century. German philosophy exercised broad influence in this century, owing in part to the dominance of the German university system. German idealists, such as Johann Gottlieb Fichte, Georg Wilhelm Friedrich Hegel, and Friedrich Wilhelm Joseph Schelling, transformed the work of Kant by maintaining that the world is constituted by a rational or mind-like process, and as such is entirely knowable. Arthur Schopenhauer's identification of this world-constituting process as an irrational will to live influenced later 19th- and early 20th-century thinking, such as the work of Friedrich Nietzsche and Sigmund Freud.

After Hegel's death in 1831, 19th-century philosophy largely turned against idealism in favor of varieties of philosophical naturalism, such as the positivism of Auguste Comte, the empiricism of John Stuart Mill, and the materialism of Karl Marx. Logic began a period of its most significant advances since the inception of the discipline, as increasing mathematical precision opened entire fields of inference to formalization in the work of George Boole and Gottlob Frege. Other philosophers who initiated lines of thought that would continue to shape philosophy into the 20th century include


 * Gottlob Frege and Henry Sidgwick, whose work in logic and ethics, respectively, provided the tools for early analytic philosophy.
 * Charles Sanders Peirce and William James, who founded pragmatism.
 * Søren Kierkegaard and Friedrich Nietzsche, who laid the groundwork for existentialism and post-structuralism.

20th-century philosophy
Within the last century, philosophy has increasingly become a professional discipline practiced within universities, like other academic disciplines. Accordingly, it has become less general and more specialized. In the view of one prominent recent historian: "Philosophy has become a highly organized discipline, done by specialists primarily for other specialists. The number of philosophers has exploded, the volume of publication has swelled, and the subfields of serious philosophical investigation have multiplied. Not only is the broad field of philosophy today far too vast to be embraced by one mind, something similar is true even of many highly specialized subfields."

In the English-speaking world, analytic philosophy became the dominant school for much of the 20th century. In the first half of the century, it was a cohesive school, shaped strongly by logical positivism, united by the notion that philosophical problems could and should be solved by attention to logic and language. The pioneering work of Bertrand Russell was a model for the early development of analytic philosophy, moving from a rejection of the idealism dominant in late 19th century British philosophy to an neo-Humean empiricism, strengthened by the conceptual resources of modern mathematical logic. In the latter half of the 20th century, analytic philosophy diffused into a wide variety of disparate philosophical views, only loosely united by historical lines of influence and a self-identified commitment to clarity and rigor. The post-war transformation of the analytic program led in two broad directions: on one hand, an interest in ordinary language as a way of avoiding or redescribing traditional philosophical problems, and on the other, a more thoroughgoing naturalism that sought to dissolve the puzzles of modern philosophy via the results of the natural sciences (such as cognitive psychology and evolutionary biology). The shift in the work of Ludwig Wittgenstein, from a view congruent with logical positivism to a therapeutic dissolution of traditional philosophy as a linguistic misunderstanding of normal forms of life, was the most influential version of the first direction in analytic philosophy. The later work of Russell and the philosophy of W.V.O. Quine are influential exemplars of the naturalist approach dominant in the second half of the 20th century. But the diversity of analytic philosophy from the 1970s onward defies easy generalization: the naturalism of Quine and his epigoni was in some precincts superseded by a "new metaphysics" of possible worlds, as in the influential work of David Lewis. Recently, the experimental philosophy movement has sought to reappraise philosophical problems through social science research techniques.

On continental Europe, no single school or temperament enjoyed dominance. The flight of the logical positivists from central Europe during the 1930s and 1940s, however, diminished philosophical interest in natural science, and an emphasis on the humanities, broadly construed, figures prominently in what is usually called "continental philosophy". 20th century movements such as phenomenology, existentialism, modern hermeneutics, critical theory, structuralism, and poststructuralism are included within this loose category. The founder of phenomenology, Edmund Husserl, sought to study consciousness as experienced from a first-person perspective, while Martin Heidegger drew on the ideas of Kierkegaard, Nietzsche, and Husserl to propose an unconventional existential approach to ontology.

Eastern philosophy
Many societies have considered philosophical questions and built philosophical traditions based upon each other's works. Eastern philosophy is a term which can refer broadly to all such traditions that originated or were popular in Asia, including Persia, India, China, Korea, Japan, and the Middle East. Or, using a stricter meaning for "philosophy", it can refer to the eastern part of the region where Abrahamic religions and Greek philosophy interacted, including the Middle East and the areas where Orthodox Christianity and Islam are traditional. For example Russia is referred to as both Eastern and Western in different contexts. Eastern philosophical traditions, and various traditions also, have influenced Western philosophers.

Babylonian philosophy
The origins of Babylonian philosophy can be traced back to the wisdom of early Mesopotamia, which embodied certain philosophies of life, particularly ethics, in the forms of dialectic, dialogues, epic poetry, folklore, hymns, lyrics, prose, and proverbs. The reasoning and rationality of the Babylonians developed beyond empirical observation. The Babylonian text Dialog of Pessimism contains similarities to the agnostic thought of the sophists, the Heraclitean doctrine of contrasts, and the dialogues of Plato, as well as a precursor to the maieutic Socratic method of Socrates and Plato. The Milesian philosopher Thales is also traditionally said to have studied philosophy in Mesopotamia.

Chinese philosophy


Philosophy has had a tremendous effect on Chinese civilization, and East Asia as a whole. Many of the great philosophical schools were formulated during the Spring and Autumn Period and Warring States Period, and came to be known as the Hundred Schools of Thought. The four most influential of these were Confucianism, Taoism, Mohism, and Legalism. Later on, during the Tang Dynasty, Buddhism from Nepal also became a prominent philosophical and religious discipline. (It should be noted that philosophy and religion were clearly distinguished in the West, whilst these concepts were more continuous in the East due to, for example, the philosophical concepts of Buddhism.) Similarly to Western philosophy, Chinese philosophy also covers a broad and complex range of thought, possessing a multitude of schools that address every branch and subject area of philosophy.

Indian philosophy
The term Indian philosophy (Sanskrit: Darshanas), may refer to any of several traditions of philosophical thought that originated in the Indian subcontinent, including Hindu philosophy, Buddhist philosophy, and Jain philosophy. Having the same or rather intertwined origins, all of these philosophies have a common underlying theme of Dharma, and similarly attempt to explain the attainment of emancipation. They have been formalized and promulgated chiefly between 1000 BC to a few centuries AD, with residual commentaries and reformations continuing up to as late as the 20th century by Aurobindo and ISKCON among others, who provided stylized interpretations.

In the history of the Indian subcontinent, following the establishment of a Vedic culture, the development of philosophical and religious thought over a period of two millennia gave rise to what came to be called the six schools of astika, or orthodox, Indian or Hindu philosophy. These schools have come to be synonymous with the greater religion of Hinduism, which was a development of the early Vedic religion.

Hindu philosophy constitutes an integral part of the culture of South Asia, and is the first of the Dharmic philosophies that were influential throughout the Far East. The great diversity in thought and practice of Hinduism is nurtured by its liberal universalism.

Persian philosophy
Persian philosophy can be traced back as far as Old Iranian philosophical traditions and thoughts, with their ancient Indo-Iranian roots. These were considerably influenced by Zarathustra's teachings. Throughout Iranian history and due to remarkable political and social influences such as the Macedonian, the Arab, and the Mongol invasions of Persia, a wide spectrum of schools of thought arose. These espoused a variety of views on philosophical questions, extending from Old Iranian and mainly Zoroastrianism-influenced traditions to schools appearing in the late pre-Islamic era, such as Manicheism and Mazdakism, as well as various post-Islamic schools. Iranian philosophy after Arab invasion of Persia is characterized by different interactions with the Old Iranian philosophy, the Greek philosophy and with the development of Islamic philosophy. The Illumination school and the Transcendent theosophy are regarded as two of the main philosophical traditions of that era in Persia. Zoroastrianism has been identified as one of the key early events in the development of philosophy.

Realism and nominalism
Realism sometimes means the position opposed to the 18th-century idealism, namely that some things have real existence outside the mind. Its standard meaning is the doctrine that abstract entities corresponding to universal terms like "man" or "table" or "red" actually exist (e.g. for Plato in a separate realm of ideas). It is opposed to nominalism, the view that abstract or universal terms are words only, or denote mental states such as ideas, beliefs, or intentions. The latter position, developed by Peter Abelard and famously held by William of Ockham, is called conceptualism.

Rationalism and empiricism
Rationalism is any view emphasizing the role or importance of human reason. Extreme rationalism tries to base all knowledge on reason alone. Rationalism typically starts from premises that cannot coherently be denied, then attempts by logical steps to deduce every possible object of knowledge.

The first rationalist, in this broad sense, is often held to be Parmenides (fl. 500 BC), who argued that it is impossible to doubt that thinking actually occurs. But thinking must have an object, therefore something beyond thinking really exists. Parmenides deduced that what really exists must have certain properties—for example, that it cannot come into existence or cease to exist, that it is a coherent whole, that it remains the same eternally (in fact, exists altogether outside time). This is known as the third man argument. Zeno of Elea (born c. 495 BC) was a disciple of Parmenides, and argued that motion is impossible, since the assertion that it exists implies a contradiction (see Zeno's arrow).

Plato (427–347 BC) was also influenced by Parmenides, but combined rationalism with a form of realism. The philosopher's work is to consider being, and the essence (ousia) of things. But the characteristic of essences is that they are universal. The nature of a man, a triangle, a tree, applies to all men, all triangles, all trees. Plato argued that these essences are mind-independent "forms", that humans (but particularly philosophers) can come to know by reason, and by ignoring the distractions of sense-perception.

Modern rationalism begins with Descartes. Reflection on the nature of perceptual experience, as well as scientific discoveries in physiology and optics, led Descartes (and also Locke) to the view that we are directly aware of ideas, rather than objects. This view gave rise to three questions:


 * 1) Is an idea a true copy of the real thing that it represents? Sensation is not a direct interaction between bodily objects and our sense, but is a physiological process involving representation (for example, an image on the retina). Locke thought that a "secondary quality" such as a sensation of green could in no way resemble the arrangement of particles in matter that go to produce this sensation, although he thought that "primary qualities" such as shape, size, number, were really in objects.
 * 2) How can physical objects such as chairs and tables, or even physiological processes in the brain, give rise to mental items such as ideas? This is part of what became known as the mind-body problem.
 * 3) If all the contents of awareness are ideas, how can we know that anything exists apart from ideas?

Descartes tried to address the last problem by reason. He began, echoing Parmenides, with a principle that he thought could not coherently be denied: I think, therefore I am (often given in his original Latin: Cogito ergo sum). From this principle, Descartes went on to construct a complete system of knowledge (which involves proving the existence of God, using, among other means, a version of the ontological argument). His view that reason alone could yield substantial truths about reality strongly influenced those philosophers usually considered modern rationalists (such as Baruch Spinoza, Gottfried Leibniz, and Christian Wolff), while provoking criticism from other philosophers who have retrospectively come to be grouped together as empiricists.

Empiricism, in contrast to rationalism, downplays or dismisses the ability of reason alone to yield knowledge of the world, preferring to base any knowledge we have on our senses. This dates back to the concept of tabula rasa (unscribed tablet) implicit in Aristotle's On the Soul, described more explicitly in Avicenna's The Book of Healing, and demonstrated in Ibn Tufail's Hayy ibn Yaqdhan as a thought experiment. Modern empiricism was notably expounded by Francis Bacon, John Locke in An Essay Concerning Human Understanding in 1689, and David Hume.

During this era, religious ideas played a mixed role in the struggles that preoccupied secular philosophy. Bishop Berkeley's famous idealist refutation of key tenets of Isaac Newton is a case of an Enlightenment philosopher who drew substantially from religious ideas. Other influential religious thinkers of the time include Blaise Pascal, Joseph Butler, Thomas Reid, and Jonathan Edwards. Other major writers, such as Jean-Jacques Rousseau and Edmund Burke, took a rather different path.

Skepticism
Skepticism is a philosophical attitude that, in its most extreme form, questions the possibility of obtaining any sort of knowledge. It was first articulated by Pyrrho, who believed that everything could be doubted except appearances. Sextus Empiricus (2nd century AD), skepticism's most prominent advocate, describes it as an "'ability to place in antithesis, in any manner whatever, appearances and judgments, and thus ... to come first of all to a suspension of judgment and then to mental tranquility.'"

Skepticism so conceived is not merely the use of doubt, but is the use of doubt for a particular end: a calmness of the soul, or ataraxia. Skepticism poses itself as a challenge to dogmatism, whose adherents think they have found the truth.

Sextus noted that the reliability of perception may always be questioned, because it is idiosyncratic to the perceiver. The appearance of individual things changes depending on whether they are in a group: for example, the shavings of a goat's horn are white when taken alone, yet the intact horn is black. A pencil, when viewed lengthwise, looks like a stick; but when examined at the tip, it looks merely like a circle.

Skepticism was revived in the early modern period by Michel de Montaigne and Blaise Pascal. Its most extreme exponent, however, was David Hume. Hume argued that there are only two kinds of reasoning: what he called probable and demonstrative (cf. Hume's fork). Neither of these two forms of reasoning can lead us to a reasonable belief in the continued existence of an external world. Demonstrative reasoning cannot do this, because demonstration (that is, deductive reasoning from well-founded premises) alone cannot establish the uniformity of nature (as captured by scientific laws and principles, for example). Such reason alone cannot establish that the future will resemble the past. We have certain beliefs about the world (that the sun will rise tomorrow, for example), but these beliefs are the product of habit and custom, and do not depend on any sort of logical inferences from what is already given certain. But probable reasoning (inductive reasoning), which aims to take us from the observed to the unobserved, cannot do this either: it also depends on the uniformity of nature, and this supposed uniformity cannot be proved, without circularity, by any appeal to uniformity. The best that either sort of reasoning can accomplish is conditional truth: if certain assumptions are true, then certain conclusions follow. So nothing about the world can be established with certainty. Hume concludes that there is no solution to the skeptical argument—except, in effect, to ignore it.

Even if these matters were resolved in every case, we would have in turn to justify our standard of justification, leading to an infinite regress (hence the term regress skepticism).

Many philosophers have questioned the value of such skeptical arguments. The question of whether we can achieve knowledge of the external world is based on how high a standard we set for the justification of such knowledge. If our standard is absolute certainty, then we cannot progress beyond the existence of mental sensations. We cannot even deduce the existence of a coherent or continuing "I" that experiences these sensations, much less the existence of an external world. On the other hand, if our standard is too low, then we admit follies and illusions into our body of knowledge. This argument against absolute skepticism asserts that the practical philosopher must move beyond solipsism, and accept a standard for knowledge that is high but not absolute.

Idealism
Idealism is the epistemological doctrine that nothing can be directly known outside of the minds of thinking beings. Or in an alternative stronger form, it is the metaphysical doctrine that nothing exists apart from minds and the "contents" of minds. In modern Western philosophy, the epistemological doctrine begins as a core tenet of Descartes—that what is in the mind is known more reliably than what is known through the senses. The first prominent modern Western idealist in the metaphysical sense was George Berkeley. Berkeley argued that there is no deep distinction between mental states, such as feeling pain, and the ideas about so-called "external" things, that appear to us through the senses. There is no real distinction, in this view, between certain sensations of heat and light that we experience, which lead us to believe in the external existence of a fire, and the fire itself. Those sensations are all there is to fire. Berkeley expressed this with the Latin formula esse est percipi: "to be is to be perceived". In this view the opinion, "strangely prevailing upon men", that houses, mountains, and rivers have an existence independent of their perception by a thinking being is false.

Forms of idealism were prevalent in philosophy from the 18th century to the early 20th century. Transcendental idealism, advocated by Immanuel Kant, is the view that there are limits on what can be understood, since there is much that cannot be brought under the conditions of objective judgment. Kant wrote his Critique of Pure Reason (1781–1787) in an attempt to reconcile the conflicting approaches of rationalism and empiricism, and to establish a new groundwork for studying metaphysics. Kant's intention with this work was to look at what we know and then consider what must be true about it, as a logical consequence of the way we know it. One major theme was that there are fundamental features of reality that escape our direct knowledge because of the natural limits of the human faculties. Although Kant held that objective knowledge of the world required the mind to impose a conceptual or categorical framework on the stream of pure sensory data—a framework including space and time themselves—he maintained that things-in-themselves existed independently of our perceptions and judgments; he was therefore not an idealist in any simple sense. Indeed, Kant's account of things-in-themselves is both controversial and highly complex. Continuing his work, Johann Gottlieb Fichte and Friedrich Schelling dispensed with belief in the independent existence of the world, and created a thoroughgoing idealist philosophy.

The most notable work of this German idealism was G. W. F. Hegel's Phenomenology of Spirit, of 1807. Hegel admitted his ideas were not new, but that all the previous philosophies had been incomplete. His goal was to correctly finish their job. Hegel asserts that the twin aims of philosophy are to account for the contradictions apparent in human experience (which arise, for instance, out of the supposed contradictions between "being" and "not being"), and also simultaneously to resolve and preserve these contradictions by showing their compatibility at a higher level of examination ("being" and "not being" are resolved with "becoming"). This program of acceptance and reconciliation of contradictions is known as the "Hegelian dialectic". Philosophers in the Hegelian tradition include Ludwig Andreas Feuerbach, who coined the term projection as pertaining to our inability to recognize anything in the external world without projecting qualities of ourselves upon those things; Karl Marx; Friedrich Engels; and the British idealists, notably T. H. Green, J. M. E. McTaggart and F. H. Bradley.

Few 20th century philosophers have embraced idealism. However, quite a few have embraced Hegelian dialectic. Immanuel Kant's "Copernican Turn" also remains an important philosophical concept today.

Pragmatism
Pragmatism was founded in the spirit of finding a scientific concept of truth that does not depend on personal insight (revelation) or reference to some metaphysical realm. The truth of a statement should be judged by the effect it has on our actions, and truth should be seen as what the whole of scientific enquiry ultimately agrees on. This should probably be seen as a guiding principle more than a definition of what it means for something to be true, though the details of how this principle should be interpreted have been subject to discussion since Charles S. Peirce first conceived it. Peirce's maxim of pragmatism is as follows: "Consider what effects, which might conceivably have practical bearings, we conceive the object of our conception to have. Then, our conception of these effects is the whole of our conceptions of the object." Like postmodern neo-pragmatist Richard Rorty, many are convinced that pragmatism asserts that the truth of beliefs does not consist in their correspondence with reality, but in their usefulness and efficacy.

The late 19th-century American philosophers Charles Sanders Peirce and William James were its co-founders, and it was later developed by John Dewey as instrumentalism. Since the usefulness of any belief at any time might be contingent on circumstance, Peirce and James conceptualised final truth as something only established by the future, final settlement of all opinion. Critics have accused pragmatism of falling victim to a simple fallacy: because something that is true proves useful, that usefulness is the basis for its truth. Thinkers in the pragmatist tradition have included John Dewey, George Santayana, W. V. O. Quine and C. I. Lewis. Pragmatism has more recently been taken in new directions by Richard Rorty, John Lachs, Donald Davidson, Susan Haack, and Hilary Putnam.

Phenomenology
Edmund Husserl's phenomenology was an ambitious attempt to lay the foundations for an account of the structure of conscious experience in general. An important part of Husserl's phenomenological project was to show that all conscious acts are directed at or about objective content, a feature that Husserl called intentionality.

In the first part of his two-volume work, the Logical Investigations (1901), he launched an extended attack on psychologism. In the second part, he began to develop the technique of descriptive phenomenology, with the aim of showing how objective judgments are indeed grounded in conscious experience—not, however, in the first-person experience of particular individuals, but in the properties essential to any experiences of the kind in question.

He also attempted to identify the essential properties of any act of meaning. He developed the method further in Ideas (1913) as transcendental phenomenology, proposing to ground actual experience, and thus all fields of human knowledge, in the structure of consciousness of an ideal, or transcendental, ego. Later, he attempted to reconcile his transcendental standpoint with an acknowledgement of the intersubjective life-world in which real individual subjects interact. Husserl published only a few works in his lifetime, which treat phenomenology mainly in abstract methodological terms; but he left an enormous quantity of unpublished concrete analyses.

Husserl's work was immediately influential in Germany, with the foundation of phenomenological schools in Munich and Göttingen. Phenomenology later achieved international fame through the work of such philosophers as Martin Heidegger (formerly Husserl's research assistant), Maurice Merleau-Ponty, and Jean-Paul Sartre. Indeed, through the work of Heidegger and Sartre, Husserl's focus on subjective experience influenced aspects of existentialism.

Existentialism
Existentialism is a term applied to the work of a number of late 19th- and 20th-century philosophers who, despite profound doctrinal differences, shared the belief that philosophical thinking begins with the human subject—not merely the thinking subject, but the acting, feeling, living human individual. In existentialism, the individual's starting point is characterized by what has been called "the existential attitude", or a sense of disorientation and confusion in the face of an apparently meaningless or absurd world. Many existentialists have also regarded traditional systematic or academic philosophy, in both style and content, as too abstract and remote from concrete human experience.

Although they did not use the term, the 19th-century philosophers Søren Kierkegaard and Friedrich Nietzsche are widely regarded as the fathers of existentialism. Their influence, however, has extended beyond existentialist thought.

The main target of Kierkegaard's writings was the idealist philosophical system of Hegel which, he thought, ignored or excluded the inner subjective life of living human beings. Kierkegaard, conversely, held that "truth is subjectivity", arguing that what is most important to an actual human being are questions dealing with an individual's inner relationship to existence. In particular, Kierkegaard, a Christian, believed that the truth of religious faith was a subjective question, and one to be wrestled with passionately.

Although Kierkegaard and Nietzsche were among his influences, the extent to which the German philosopher Martin Heidegger should be considered an existentialist is debatable. In Being and Time he presented a method of rooting philosophical explanations in human existence (Dasein) to be analysed in terms of existential categories (existentiale); and this has led many commentators to treat him as an important figure in the existentialist movement. However, in The Letter on Humanism, Heidegger explicitly rejected the existentialism of Jean-Paul Sartre.

Sartre became the best-known proponent of existentialism, exploring it not only in theoretical works such as Being and Nothingness, but also in plays and novels. Sartre, along with Simone de Beauvoir, represented an avowedly atheistic branch of existentialism, which is now more closely associated with their ideas of nausea, contingency, bad faith, and the absurd than with Kierkegaard's spiritual angst. Nevertheless, the focus on the individual human being, responsible before the universe for the authenticity of his or her existence, is common to all these thinkers.

Structuralism and post-structuralism
Inaugurated by the linguist Ferdinand de Saussure, structuralism sought to clarify systems of signs through analyzing the discourses they both limit and make possible. Saussure conceived of the sign as being delimited by all the other signs in the system, and ideas as being incapable of existence prior to linguistic structure, which articulates thought. This led continental thought away from humanism, and toward what was termed the decentering of man: language is no longer spoken by man to express a true inner self, but language speaks man.

Structuralism sought the province of a hard science, but its positivism soon came under fire by poststructuralism, a wide field of thinkers, some of whom were once themselves structuralists, but later came to criticize it. Structuralists believed they could analyze systems from an external, objective standing, for example, but the poststructuralists argued that this is incorrect, that one cannot transcend structures and thus analysis is itself determined by what it examines, while the distinction between the signifier and signified was treated as crystalline by structuralists, poststructuralists asserted that every attempt to grasp the signified results in more signifiers, so meaning is always in a state of being deferred, making an ultimate interpretation impossible.

Structuralism came to dominate continental philosophy throughout the 1960s and early '70s, encompassing thinkers as diverse as Claude Lévi-Strauss, Roland Barthes and Jacques Lacan. Post-structuralism came to predominate over the 1970s onwards, including thinkers such as Michel Foucault, Jacques Derrida, Gilles Deleuze and even Roland Barthes; it incorporated a critique of structuralism's limitations.

The analytic tradition
The term analytic philosophy roughly designates a group of philosophical methods that stress detailed argumentation, attention to semantics, use of classical logic and non-classical logics and clarity of meaning above all other criteria. Some have held that philosophical problems arise through misuse of language or because of misunderstandings of the logic of our language, while some maintain that there are genuine philosophical problems and that philosophy is continuous with science. Michael Dummett in his Origins of Analytical Philosophy makes the case for counting Gottlob Frege's The Foundations of Arithmetic as the first analytic work, on the grounds that in that book Frege took the linguistic turn, analyzing philosophical problems through language. Bertrand Russell and G.E. Moore are also often counted as founders of analytic philosophy, beginning with their rejection of British idealism, their defense of realism and the emphasis they laid on the legitimacy of analysis. Russell's classic works The Principles of Mathematics, On Denoting and Principia Mathematica with Alfred North Whitehead, aside from greatly promoting the use of mathematical logic in philosophy, set the ground for much of the research program in the early stages of the analytic tradition, emphasizing such problems as: the reference of proper names, whether 'existence' is a property, the nature of propositions, the analysis of definite descriptions, the discussions on the foundations of mathematics; as well as exploring issues of ontological commitment and even metaphysical problems regarding time, the nature of matter, mind, persistence and change, which Russell tackled often with the aid of mathematical logic. Russell and Moore's philosophy, in the beginning of the 20th century, developed as a critique of Hegel and his British followers in particular, and of grand systems of speculative philosophy in general, though by no means all analytic philosophers reject the philosophy of Hegel (see Charles Taylor) nor speculative philosophy. Some schools in the group include logical positivism, and ordinary language both markedly influenced by Russell and Wittgenstein's development of Logical Atomism the former positively and the latter negatively.

In 1921, Ludwig Wittgenstein, who studied under Russell at Cambridge, published his Tractatus Logico-Philosophicus, which gave a rigidly "logical" account of linguistic and philosophical issues. At the time, he understood most of the problems of philosophy as mere puzzles of language, which could be solved by investigating and then minding the logical structure of language. Years later, he reversed a number of the positions he set out in the Tractatus, in for example his second major work, Philosophical Investigations (1953). Investigations was influential in the development of "ordinary language philosophy," which was promoted by Gilbert Ryle, J.L. Austin, and a few others. In the United States, meanwhile, the philosophy of W.V.O. Quine was having a major influence, with such classics as Two Dogmas of Empiricism. In that paper Quine criticizes the distinction between analytic and synthetic statements, arguing that a clear conception of analyticity is unattainable. He argued for holism, the thesis that language, including scientific language, is a set of interconnected sentences, none of which can be verified on its own, rather, the sentences in the language depend on each other for their meaning and truth conditions. A consequence of Quine's approach is that language as a whole has only a thin relation to experience. Some sentences that refer directly to experience might be modified by sense impressions, but as the whole of language is theory-laden, for the whole language to be modified, more than this is required. However, most of the linguistic structure can in principle be revised, even logic, in order to better model the world. Notable students of Quine include Donald Davidson and Daniel Dennett. The former devised a program for giving a semantics to natural language and thereby answer the philosophical conundrum "what is meaning?". A crucial part of the program was the use of Alfred Tarski's semantic theory of truth. Dummett, among others, argued that truth conditions should be dispensed within the theory of meaning, and replaced by assertibility conditions. Some propositions, on this view, are neither true nor false, and thus such a theory of meaning entails a rejection of the law of the excluded middle. This, for Dummett, entails antirealism, as Russell himself pointed out in his An Inquiry into Meaning and Truth.

By the 1970s there was a renewed interest in many traditional philosophical problems by the younger generations of analytic philosophers. David Lewis, Saul Kripke, Derek Parfit and others took an interest in traditional metaphysical problems, which they began exploring by the use of logic and philosophy of language. Among those problems some distinguished ones were: free will, essentialism, the nature of personal identity, identity over time, the nature of the mind, the nature of causal laws, space-time, the properties of material beings, modality, etc. In those universities where analytic philosophy has spread, these problems are still being discussed passionately. Analytic philosophers are also interested in the methodology of analytic philosophy itself, with Timothy Williamson, Wykeham Professor of Logic at Oxford, publishing recently a book entitled The Philosophy of Philosophy. Some influential figures in contemporary analytic philosophy are: Timothy Williamson, David Lewis, John Searle, Thomas Nagel, Hilary Putnam, Michael Dummett, Peter van Inwagen and Saul Kripke. Analytic philosophy has sometimes been accused of not contributing to the political debate or to traditional questions in aesthetics. However, with the appearance of A Theory of Justice by John Rawls and Anarchy, State and Utopia by Robert Nozick, analytic political philosophy acquired respectability. Analytic philosophers have also shown depth in their investigations of aesthetics, with Roger Scruton, Nelson Goodman, Arthur Danto and others developing the subject to its current shape.

Human nature and political legitimacy


From ancient times, and well beyond them, the roots of justification for political authority were inescapably tied to outlooks on human nature. In The Republic, Plato presented the argument that the ideal society would be run by a council of philosopher-kings, since those best at philosophy are best able to realize the good. Even Plato, however, required philosophers to make their way in the world for many years before beginning their rule at the age of fifty. For Aristotle, humans are political animals (i.e. social animals), and governments are set up to pursue good for the community. Aristotle reasoned that, since the state (polis) was the highest form of community, it has the purpose of pursuing the highest good. Aristotle viewed political power as the result of natural inequalities in skill and virtue. Because of these differences, he favored an aristocracy of the able and virtuous. For Aristotle, the person cannot be complete unless he or she lives in a community. His The Nicomachean Ethics and The Politics are meant to be read in that order. The first book addresses virtues (or "excellences") in the person as a citizen; the second addresses the proper form of government to ensure that citizens will be virtuous, and therefore complete. Both books deal with the essential role of justice in civic life.

Nicolas of Cusa rekindled Platonic thought in the early 15th century. He promoted democracy in Medieval Europe, both in his writings and in his organization of the Council of Florence. Unlike Aristotle and the Hobbesian tradition to follow, Cusa saw human beings as equal and divine (that is, made in God's image), so democracy would be the only just form of government. Cusa's views are credited by some as sparking the Italian Renaissance, which gave rise to the notion of "Nation-States".

Later, Niccolò Machiavelli rejected the views of Aristotle and Thomas Aquinas as unrealistic. The ideal sovereign is not the embodiment of the moral virtues; rather the sovereign does whatever is successful and necessary, rather than what is morally praiseworthy. Thomas Hobbes also contested many elements of Aristotle's views. For Hobbes, human nature is essentially anti-social: people are essentially egoistic, and this egoism makes life difficult in the natural state of things. Moreover, Hobbes argued, though people may have natural inequalities, these are trivial, since no particular talents or virtues that people may have will make them safe from harm inflicted by others. For these reasons, Hobbes concluded that the state arises from a common agreement to raise the community out of the state of nature. This can only be done by the establishment of a sovereign, in which (or whom) is vested complete control over the community, and is able to inspire awe and terror in its subjects.

Many in the Enlightenment were unsatisfied with existing doctrines in political philosophy, which seemed to marginalize or neglect the possibility of a democratic state. Jean-Jacques Rousseau was among those who attempted to overturn these doctrines: he responded to Hobbes by claiming that a human is by nature a kind of "noble savage", and that society and social contracts corrupt this nature. Another critic was John Locke. In Second Treatise on Government he agreed with Hobbes that the nation-state was an efficient tool for raising humanity out of a deplorable state, but he argued that the sovereign might become an abominable institution compared to the relatively benign unmodulated state of nature.

Following the doctrine of the fact-value distinction, due in part to the influence of David Hume and his student Adam Smith, appeals to human nature for political justification were weakened. Nevertheless, many political philosophers, especially moral realists, still make use of some essential human nature as a basis for their arguments.

Marxism is derived from the work of Karl Marx and Friedrich Engels. Their idea that capitalism is based on exploitation of workers and causes alienation of people from their human nature, the historical materialism, their view of social classes, etc., have influenced many fields of study, such as sociology, economics, and politics. Marxism inspired the Marxist school of communism, which brought a huge impact on the history of the 20th century.

Consequentialism, deontology, and the aretaic turn
One debate that has commanded the attention of ethicists in the modern era has been between consequentialism (actions are to be morally evaluated solely by their consequences) and deontology (actions are to be morally evaluated solely by consideration of agents' duties, the rights of those whom the action concerns, or both).

Jeremy Bentham and John Stuart Mill are famous for propagating utilitarianism, which is the idea that the fundamental moral rule is to strive toward the "greatest happiness for the greatest number". However, in promoting this idea they also necessarily promoted the broader doctrine of consequentialism.

Adopting a position opposed to consequentialism, Immanuel Kant argued that moral principles were simply products of reason. Kant believed that the incorporation of consequences into moral deliberation was a deep mistake, since it denies the necessity of practical maxims in governing the working of the will. According to Kant, reason requires that we conform our actions to the categorical imperative, which is an absolute duty. An important 20th-century deontologist, W.D. Ross, argued for weaker forms of duties called prima facie duties.

More recent works have emphasized the role of character in ethics, a movement known as the aretaic turn (that is, the turn towards virtues). One strain of this movement followed the work of Bernard Williams. Williams noted that rigid forms of consequentialism and deontology demanded that people behave impartially. This, Williams argued, requires that people abandon their personal projects, and hence their personal integrity, in order to be considered moral.

G.E.M. Anscombe, in an influential paper, "Modern Moral Philosophy" (1958), revived virtue ethics as an alternative to what was seen as the entrenched positions of Kantianism and consequentialism. Aretaic perspectives have been inspired in part by research of ancient conceptions of virtue. For example, Aristotle's ethics demands that people follow the Aristotelian mean, or balance between two vices; and Confucian ethics argues that virtue consists largely in striving for harmony with other people. Virtue ethics in general has since gained many adherents, and has been defended by such philosophers as Philippa Foot, Alasdair MacIntyre, and Rosalind Hursthouse.

Applied philosophy
The ideas conceived by a society have profound repercussions on what actions the society performs. The applied study of philosophy yields applications such as those in ethics—applied ethics in particular—and political philosophy. The political and economic philosophies of Confucius, Sun Zi, Chanakya, Ibn Khaldun, Ibn Rushd, Ibn Taimiyyah, Niccolò Machiavelli, Gottfried Leibniz, John Locke, Jean-Jacques Rousseau, Adam Smith, Karl Marx, John Stuart Mill, Mahatma Gandhi, Martin Luther King Jr. and others—all of these have been used to shape and justify governments and their actions.

In the field of philosophy of education, progressive education as championed by John Dewey has had a profound impact on educational practices in the United States in the 20th century. Descendants of this movement include the current efforts in philosophy for children, which are part of philosophy education. Carl von Clausewitz's political philosophy of war has had a profound effect on statecraft, international politics, and military strategy in the 20th century, especially in the years around World War II. Logic has become crucially important in mathematics, linguistics, psychology, computer science, and computer engineering.

Other important applications can be found in epistemology, which aid in understanding the requisites for knowledge, sound evidence, and justified belief (important in law, economics, decision theory, and a number of other disciplines). The philosophy of science discusses the underpinnings of the scientific method and has affected the nature of scientific investigation and argumentation. As such, philosophy has fundamental implications for science as a whole. For example, the strictly empirical approach of Skinner's behaviorism affected for decades the approach of the American psychological establishment. Deep ecology and animal rights examine the moral situation of humans as occupants of a world that has non-human occupants to consider also. Aesthetics can help to interpret discussions of music, literature, the plastic arts, and the whole artistic dimension of life. In general, the various philosophies strive to provide practical activities with a deeper understanding of the theoretical or conceptual underpinnings of their fields.

Often philosophy is seen as an investigation into an area not sufficiently well understood to be its own branch of knowledge. What were once philosophical pursuits have evolved into the modern day fields such as psychology, sociology, linguistics, and economics, for example.

The New York Times reported an increase in philosophy majors at United States universities in 2008.

Introductions

 * Appiah, Kwame Anthony. Thinking it Through – An Introduction to Contemporary Philosophy, 2003, ISBN 0-19-513458-3
 * Blumenau, Ralph. Philosophy and Living. ISBN 0-907845-33-9
 * Craig, Edward. Philosophy: A Very Short Introduction. ISBN 0-19-285421-6
 * Curley, Edwin, A Spinoza Reader, Princeton, 1994, ISBN 0-691-00067-0
 * Durant, Will, Story of Philosophy: The Lives and Opinions of the World's Greatest Philosophers, Pocket, 1991, ISBN 0-671-73916-6, ISBN 978-0-671-73916-4
 * Harrison-Barbet, Anthony, Mastering Philosophy. ISBN 0-333-69343-4
 * Higgins, Kathleen M. and Solomon, Robert C. A Short History of Philosophy. ISBN 0-19-510196-0
 * Philosophy Now magazine
 * Russell, Bertrand. The Problems of Philosophy. ISBN 0-19-511552-X
 * Sinclair, Alistair J. What is Philosophy? An Introduction, 2008, ISBN 978-1-903765-94-4
 * Sober, E. (2001). Core Questions in Philosophy: A Text with Readings. Upper Saddle River, Prentice Hall. ISBN 0-13-189869-8
 * Solomon, Robert C. Big Questions: A Short Introduction to Philosophy. ISBN 0-534-16708-X
 * Warburton, Nigel. Philosophy: The Basics. ISBN 0-415-14694-1
 * Think: philosophy for everyone Lively and accessible articles written by philosophers pre-eminent in their fields, for a broad audience. Free articles are available online.

Topical introductions

 * Copleston, Frederick. Philosophy in Russia: From Herzen to Lenin and Berdyaev. ISBN 0-268-01569-4
 * Critchley, Simon. Continental Philosophy: A Very Short Introduction. ISBN 0-19-285359-7
 * Hamilton, Sue. Indian Philosophy: a Very Short Introduction. ISBN 0-19-285374-0
 * Harwood, Sterling, ed., Business as Ethical and Business as Usual (Belmont, CA: Wadsworth Publishing Co., 2000); www.sterlingharwood.com
 * Imbo, Samuel Oluoch. '3'An Introduction to African Philosophy''. ISBN 0-8476-8841-0
 * Knight, Kelvin. Aristotelian Philosophy: Ethics and Politics from Aristotle to MacIntyre. ISBN 0-7456-1977-0
 * Kupperman, Joel J. Classic Asian Philosophy: A Guide to the Essential Texts. ISBN 0-19-513335-8
 * Leaman, Oliver. A Brief Introduction to Islamic Philosophy. ISBN 0-7456-1960-6
 * Lee, Joe and Powell, Jim. Eastern Philosophy For Beginners. ISBN 0-86316-282-7
 * Nagel, Thomas. What Does It All Mean? A Very Short Introduction to Philosophy. ISBN 0-19-505292-7
 * Scruton, Roger. A Short History of Modern Philosophy. ISBN 0-415-26763-3
 * Smart, Ninian. World Philosophies. ISBN 0-415-22852-2
 * Tarnas, Richard. The Passion of the Western Mind: Understanding the Ideas That Have Shaped Our World View. ISBN 0-345-36809-6

Anthologies

 * Classics of Philosophy (Vols. 1 & 2, 2nd edition) by Louis P. Pojman
 * Classics of Philosophy: The 20th Century (Vol. 3) by Louis P. Pojman
 * The English Philosophers from Bacon to Mill by Edwin Arthur
 * European Philosophers from Descartes to Nietzsche by Monroe Beardsley
 * Contemporary Analytic Philosophy: Core Readings by James Baillie
 * Existentialism: Basic Writings (Second Edition) by Charles Guignon, Derk Pereboom
 * The Phenomenology Reader by Dermot Moran, Timothy Mooney
 * Medieval Islamic Philosophical Writings edited by Muhammad Ali Khalidi
 * A Source Book in Indian Philosophy by Sarvepalli Radhakrishnan, Charles A. Moore
 * A Source Book in Chinese Philosophy by Wing-tsit Chan
 * Kim, J. and Ernest Sosa, Ed. (1999). Metaphysics: An Anthology. Blackwell Philosophy Anthologies. Oxford, Blackwell Publishers Ltd.
 * The Oxford Handbook of Free Will (2004) edited by Robert Kane
 * Husserl, Edmund and Donn Welton (1999). The Essential Husserl: Basic Writings in Transcendental Phenomenology, Indiana University Press. ISBN 0-253-21273-1
 * Cottingham, John. Western Philosophy: An Anthology. 2nd ed. Malden, MA: Blackwell Pub., 2008. Print. Blackwell Philosophy Anthologies.

Reference works

 * The Oxford Companion to Philosophy edited by Ted Honderich
 * The Cambridge Dictionary of Philosophy by Robert Audi
 * The Routledge Encyclopedia of Philosophy (10 vols.) edited by Edward Craig, Luciano Floridi (available online by subscription); or
 * The Concise Routledge Encyclopedia of Philosophy edited by Edward Craig (an abridgement)
 * Encyclopedia of Philosophy (8 vols.) edited by Paul Edwards; in 1996, a ninth supplemental volume appeared that updated the classic 1967 encyclopedia.
 * International Directory of Philosophy and Philosophers. Charlottesville, Philosophy Documentation Center.
 * Directory of American Philosophers. Charlottesville, Philosophy Documentation Center.
 * Routledge History of Philosophy (10 vols.) edited by John Marenbon
 * History of Philosophy (9 vols.) by Frederick Copleston
 * A History of Western Philosophy (5 vols.) by W. T. Jones
 * History of Italian Philosophy (2 vols.) by Eugenio Garin. Translated from Italian and Edited by Giorgio Pinton. Introduction by Leon Pompa.
 * Encyclopaedia of Indian Philosophies (8 vols.), edited by Karl H. Potter et al. (first 6 volumes out of print)
 * Indian Philosophy (2 vols.) by Sarvepalli Radhakrishnan
 * A History of Indian Philosophy (5 vols.) by Surendranath Dasgupta
 * History of Chinese Philosophy (2 vols.) by Fung Yu-lan, Derk Bodde
 * Encyclopedia of Chinese Philosophy edited by Antonio S. Cua
 * Encyclopedia of Eastern Philosophy and Religion by Ingrid Fischer-Schreiber, Franz-Karl Ehrhard, Kurt Friedrichs
 * Companion Encyclopedia of Asian Philosophy by Brian Carr, Indira Mahalingam
 * A Concise Dictionary of Indian Philosophy: Sanskrit Terms Defined in English by John A. Grimes
 * History of Islamic Philosophy edited by Seyyed Hossein Nasr, Oliver Leaman
 * History of Jewish Philosophy edited by Daniel H. Frank, Oliver Leaman
 * A History of Russian Philosophy: From the Tenth to the Twentieth Centuries by Valerii Aleksandrovich Kuvakin
 * Ayer, A.J. et al., Ed. (1994) A Dictionary of Philosophical Quotations. Blackwell Reference Oxford. Oxford, Basil Blackwell Ltd.
 * Blackburn, S., Ed. (1996)The Oxford Dictionary of Philosophy. Oxford, Oxford University Press.
 * Mauter, T., Ed. The Penguin Dictionary of Philosophy. London, Penguin Books.
 * Runes, D., Ed. (1942). The Dictionary of Philosophy. New York, The Philosophical Library, Inc.
 * Angeles, P.A., Ed. (1992). The Harper Collins Dictionary of Philosophy. New York, Harper Perennial.
 * Bunnin, N. et al., Ed. (1996) The Blackwell Companion to Philosophy. Blackwell Companions to Philosophy. Oxford, Blackwell Publishers Ltd.
 * Hoffman, Eric, Ed. (1997) Guidebook for Publishing Philosophy. Charlottesville, Philosophy Documentation Center.
 * Popkin, R.H. (1999). The Columbia History of Western Philosophy. New York, Columbia University Press.