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. 489 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:
# 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.
# 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.
# 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. John Locke propounded the classic empiricist view in ''An Essay Concerning Human Understanding'' in 1689, developing a form of naturalism and empiricism on roughly scientific (and Newtonian) principles.
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. The restricted interests of many of the philosophers of the time foreshadow the separation and specialization of different areas of philosophy that occurred in the 20th century.
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 weren't 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 didn't 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 (who came to critique structrualism'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. Michael Dummett in his ''Origins of Analytical Philosophy'' makes the case for counting Gottlob Frege ''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'', aside from greatly promoting the use of classical first order 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 meaning of propositions, the analysis of definite descriptions, the discussions on the foundations of mathematics; as well as exploring issues of metaphysical 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. The philosophy developed as a critique of Hegel and his 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 atomism, logical positivism, and ordinary language. The motivation behind the work of analytic philosophers has been varied. 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.In 1921, Ludwig Wittgenstein 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 ''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 notable figures in contemporary analytic philosophy are: Timothy Williamson, John Searle, Thomas Nagel, Hilary Putnam, Michael Dummett, 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, Richard Wollheim, Jerrold Levinson and others developing the subject to its current shape.
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