Logical positivism originated in the Vienna Circle in the 1920s, where Rudolf Carnap , Otto Neurath , and others (see Philosophers Associated With Logical Positivism in this article) divided statements into those which are Analytic (true ''a priori''), and those which are Synthetic (verified by sensory experience). This was perhaps presaged by Hume's Fork . Logical positivism holds that philosophy should aspire to the Rigor of Science . Philosophy should provide strict criteria for judging sentences true, false, and meaningless.
Although the logical positivists held a wide range of beliefs on many matters, they all shared an interest in science and a deep skepticism of the Theological and Metaphysical . Following Ludwig Wittgenstein , many subscribed to the Correspondence Theory Of Truth , although some, like Neurath, believed in Coherentism . They believed that all knowledge should be based on logical inference from simple "protocol sentences" grounded in observable facts. Hence, many logical positivists supported forms of Realism , Materialism , Philosophical Naturalism , and Empiricism .
Logical positivism is perhaps best known for the Verifiability Criterion Of Meaning , which asserts that a statement is meaningful if and only if it is empirically verifiable. One intended consequence of the verification criterion is that all non-empirical forms of discourse, including Ethics and Aesthetics , are not "literally" or "cognitively" meaningful, and thus belong to " Metaphysics ".
The logical positivists were very much influenced by and were great admirers of the early work of Wittgenstein (from the period of the '' Tractatus Logico-Philosophicus ''). Wittgenstein himself was not a logical positivist, although he was on friendly terms with many members of the Vienna Circle while in Vienna, especially fellow aristrocrat Moritz Schlick . Wittgenstein's influence is evident in the formulation of the Verifiability Principle . See for example ''Proposition 4.024'' of the ''Tractatus'', where Wittgenstein asserts that we understand a proposition when we know what happens if it is true, and compare it with Schlick's assertion that "The definition of the circumstances under which a statement is true is perfectly 'equivalent' to the definition of its meaning". Wittgenstein also influenced the logical positivists' interpretation of Probability .
However, Wittgenstein's relations were not entirely amicable after he left Vienna. Wittgenstein worked mostly in cooperation for nearly a decade with Circle member utterances, using him as a secretary and speaking of cooperating on a book with him. When Waismann came to Cambridge in 1937, Wittgenstein barely acknowledged him.
Not all logical positivists' reactions to the ''Tractatus'' were positive: according to Neurath, it was full of metaphysics. Carnap (in his autobiography in ''The Philosophy of Rudolf Carnap'') said that Wittgenstein's influence on the Vienna Circle was overestimated. Moreover, Wittgenstein did not take part in the Vienna Circle's discussions; there were separate meetings between him, Schlick, Carnap and Waismann, but soon Carnap was not admitted to those meetings.
Logical positivism was essential to the development of early Analytic Philosophy . It was disseminated throughout the European continent and, later, in American universities by the members of the Vienna Circle. A.J. Ayer is considered responsible for the spread of logical positivism to Britain. The term subsequently came to be almost interchangeable with "analytic philosophy" in the first half of the twentieth century. Logical positivism was immensely influential in the Philosophy Of Language and represented the dominant Philosophy Of Science between World War I and the Cold War . Many subsequent commentators on "logical positivism" have attributed to its proponents a greater unity of purpose and creed than they actually shared, overlooking the complex disagreements among the logical positivists themselves.
An important objective pursued by logical positivism was "unified science"; that is, the construction of a "constitutive system" in which every legitimate Statement is reduced to the Concept s of a lower level which refer directly to a given Experience . A number of publications over a period of thirty years would attempt to elucidate this concept.
The Vienna Circle published a collection called ''Einheitswissenschaft'' (''Unified Science'')—edited by Rudolf Carnap , Philipp Frank , Hans Hahn , Otto Neurath , Jorgen Jorgensen (after Hahn's death) and Charles Morris —the aim of which was to present a Unified Vision Of Science . The collection was dismissed, after the publication of several Monographies , because of the problems arising from World War II . The list of philosophers and scientists who contributed to these works is impressive. The complete list of contributors is given here for the historical record.
''Einheitswissenschaft'' (''Unified Science''), edited by Carnap, Frank, Hahn, Neurath, Jorgensen (after Hahn's death), and Morris (from 1938):
- Hans Hahn , ''Logik, Mathematik und Naturerkennen'', 1933
- Otto Neurath , ''Einheitswissenschaft und Psychologie'', 1933
- Rudolf Carnap , ''Die Aufgabe der Wissenschaftlogik'', 1934
- Philipp Frank , ''Das Ende der mechanistischen Physik'', 1935
- Otto Neurath, ''Was bedeutet rationale Wirtschaftsbetrachtung'', 1935
- Otto Neurath, E. Brunswik, C. Hull, G. Mannoury, J. Woodger, ''Zur Enzyklopädie der Einheitswissenschaft''. Vorträge, 1938
- Richard Von Mises , ''Ernst Mach und die empiristische Wissenschaftauffassung'', 1939
These works are translated in ''Unified Science: The Vienna Circle Monograph Series'', originally edited by Otto Neurath:, Kluwer, 1987.
In 1938 the publication of the '' International Encyclopedia Of Unified Science '' started under the auspice of logical positivists. It was an ambitious project, and never completed. Only the first section, ''Foundations of the Unity of Sciences'', was published; it contained two volumes, for a total of twenty monographs published from 1938 to 1969:
- Otto Neurath , Niels Bohr , John Dewey , Bertrand Russell , Rudolf Carnap , Charles Morris , ''Encyclopedia and unified science'', 1938, vol.1 n.1
- Charles Morris, ''Foundations of the theory of signs'', 1938, vol.1 n.2
- Victor Lenzen , ''Procedures of empirical sciences'', 1938, vol.1 n.5
- Rudolf Carnap , ''Foundations of logic and mathematics'', 1939, vol.1 n.3
- Leonard Bloomfield , ''Linguistic aspects of science'', 1939, vol.1 n.4
- Ernest Nagel , ''Principles of the theory of probability'', 1939, vol.1 n.6
- John Dewey , ''Theory of valuation'', 1939, vol.2 n.4
- Giorgio De Santillana and Egdard Zilsel , ''The development of rationalism and empiricism'', 1941, vol.2 n.8
- Otto Neurath, ''Foundations of social sciences'', 1944, vol.2 n.1
- Joseph Henri Woodger , ''The technique of theory construction'', 1949, vol.2 n.5
- Philipp Frank , ''Foundations of physics'', 1946, vol.1 n.7
- Erwin Frinlay-Freundlich , ''Cosmology'', 1951, vol.1 n.8
- Jorgen Jorgensen, ''The development of logical empiricism'', 1951, vol.2 n.9
- Egon Brunswik , ''The conceptual framework of psychology'', 1952, vol.1 n.10
- Carl Hempel , ''Fundamentals of concept formation in empirical science'', 1952, vol.2 n.7
- Felix Mainx , ''Foundations of biology'', 1955, vol.1 n.9
- Abraham Edel , ''Science and the structure of ethics'', 1961, vol.2 n.3
- Thomas Kuhn , ''The structure of scientific revolutions'', 1962, vol.2 n.2
- Gherard Tintner , ''Methodology of mathematical economics and econometrics'', 1968, vol.2 n.6
- Herbert Feigl and Charles Morris , ''Bibliography and index'', 1969, vol.2 n.10
Perhaps the most famous work published in the ''International Encyclopedia of Unified Science'' is Thomas Kuhn 's '' The Structure Of Scientific Revolutions ''. However, every entry in the encyclopedia is of substantial scientific and philosophical value.
A third collection was published by the Vienna Circle from 1928 to 1937. This collection was entitled ''Schriften zur wissenschaftlichen Weltauffassung'' (''Monographs on the Scientific World-Conception''), and was edited by Schlick and Frank. Scientists and philosophers such as Karl Popper contributed. The contributors and monographs were:
- Richard Von Mises , ''Wahrscheinlichkeit, Statistik und Wahrheit'', 1928 (''Probability, Statistics, and Truth'', New York: MacMillan Company, 1939)
- Rudolf Carnap , ''Abriss der Logistik'', 1929
- Moritz Schlick , ''Fragen der Ethik'', 1930 (''Problems of Ethics'', New York: Prentice-Hall, 1939)
- Otto Neurath , ''Empirische Soziologie'', 1931
- Philipp Frank , ''Das Kausalgesetz und seine Grenzen'', 1932 (''The Law of Causality and its Limits'', Dordrecth; Boston: Kluwer, 1997)
- Otto Kant , ''Zur Biologie der Ethik'', 1932
- Rudolf Carnap, ''Logische Syntax der Sprache'', 1934 (''The Logical Syntax of Language'', New York: Humanities, 1937)
- Karl Popper , ''Logik der Forschung'', 1934 (''The Logic of Scientific Discovery'', New York: Basic Books, 1959)
- Josef Schächeter , ''Prolegomena zu einer kritischen Grammatik'', 1935 (''Prolegomena to a Critical Grammar'', Dordrecth; Boston: D. Reidel Pub. Co., 1973)
- Victor Kraft , ''Die Grundlagen einer wissenschaftliche Wertlehre'', 1937 (''Foundations for a Scientific Analysis of Value'', Dordrecth; Boston: D. Reidel Pub. Co., 1981)
There is an extensive list of philosophers who are associated to some degree with logical positivism.
- The physicist and philosopher , one of the first philosophers interested in the Theory Of Relativity . He taught at the University Of Vienna , where he held the chair of theory of inductive science. In Vienna, he organized the discussion group known as the Vienna Circle. Schlick can be regarded as the father of logical positivism, both for his organizational skills and for his philosophical ideas. He formulated the Verifiability Principle .
- , one of the major philosophers of the twentieth century, a leading exponent of logical positivism, and co-author of the Vienna Circle manifesto. He made contributions to the Philosophy Of Science , the Philosophy Of Language , the theory of Probability , and classical, inductive and modal Logic . Since ordinary language is ambiguous, Carnap asserted the necessity to study philosophical issues in artificial languages, governed by the rules of Logic and Mathematics . In such languages he dealt with problems like the meaning of a Statement , the distinction between Analytic and Synthetic , '' A Priori '' and '' A Posteriori '', Necessity and Contingency , the different interpretations of Probability , and the nature of Explanation . Carnap taught at the University Of Prague , the University Of Vienna , the University Of Chicago , Harvard University , and the University Of California At Los Angeles .
- The philosopher of science ''' and at the University Of Minnesota , where in 1953 he founded the Minnesota Center for the Philosophy of Science, the oldest center for the Philosophy Of Science in the world.
- The physicist , a student of David Hilbert and Ludwig Boltzmann , who was an editor of the series ''Monographs on the Scientific World-Conception'' and ''Unified Science''; he contributed to the ''International Encyclopedia of Unified Science'' with the 1946 work "Foundations of physics".. He taught at Harvard University and wrote about the Theory Of Relativity .
- The logician and mathematician , who proved the completeness of First Order Logic and the Incompleteness of formal arithmetic. Gödel also worked on Set Theory and non-classical logics, such as Intuitionistic Logic and Modal Logic . He proved that the Continuum Hypothesis is consistent with the axioms of classical set theory. He was interested in the mathematical aspects of the Theory Of Relativity , and proved the existence of solutions of Einstein ’s relativistic equations in which time travels to the past are possible.
- The mathematician , co-author of the Vienna Circle manifesto, who taught at Innsbruck , Bonn and Vienna ; among his students there were Karl Popper and Kurt Gödel .
- The philosopher and sociologist , who played an important role in the development of logical positivism. He was co-author of the manifesto of the Vienna Circle (it is supposed that he was indeed the principal author), planned and directed the ''International Encyclopedia of Unified Science'', was an editor of the journal ''Erkentnnis'' and of the series ''Unified Science'', and founded and directed the International Foundation for Visual Education.
- The philosopher , who was one of the few members of the Vienna Circle admitted to the meetings with Wittgenstein . He taught philosophy of mathematics and philosophy of science at the University Of Cambridge and at the University Of Oxford .
In Germany, members of the Berlin Circle contributed in an essential way to the development of logical positivism:
- The physicist and philosopher , the founder of the Berlin Circle . He studied with Albert Einstein , Arnold Sommerfeld , Ernst Cassirer , David Hilbert , Max Planck , and Max Born . He is one of the father of the frequency intrerpretation of Probability . He taught physics at Tecnische Hochschule in Stuttgart , philosophy of physics at the University Of Berlin ; he was chief of the department of philosophy at the University Of Istanbul ; he taught philosophy at the University Of California At Los Angeles . He wrote about the philosophical meaning of the Theory Of Relativity , which he studied under the teaching of Albert Einstein , and Quantum Mechanics .
- The logician and philosopher , a victim of Nazism ; is it supposed that he died with his wife in the Auschwitz concentration camp in 1942, although it also has been reported that Grelling was killed in 1941 at the border between France and Spain while he was trying to escape in Spain. Grelling was a teacher in secondary school and was interested in logical problems. A semantic paradox is named after him, the Grelling Paradox , formulated in 1908] by Grelling and Leonard Nelson . Grelling collaborated with Kurt Gödel and in 1936 he published an article in which he defended Gödel's theorem of incompleteness against an erroneous interpretation, according to which Gödel's theorem is indeed a paradox like Russell's paradox.
- The philosopher , a leading member of logical positivism. He studied philosophy with Hans Reichenbach , physics with Max Planck , logic with Von Neumann and mathematics with David Hilbert . He taught in New York , at the City College and at Queens College . Later, Hempel taught at Yale University , at the Princeton University and, well on in years, he continued in teaching at the University Of California At Berkley and Irvine , the Hebrew University Of Jerusalem , and the University Of Pittsburgh . He contributed to the ''International Encyclopedia of Unified Science''. He is well-known for his studies on the logic of Confirmation and Explanation .
- As early as 1930 Scandinavian philosophers were interested in logical positivism. Two of them, Swedish and Finnish ''' Eino Kaila ''', employed for the first time the expression "logical neopositivism" for denoting the new philosophical movements (A. Petzäll, ''Der logistische Neupositivismus'', 1930; and E. Kaila, "Der logistische Neupositivismus" in ''Annales Universitatis Aboensis'', 1930). Petzäll was mainly influenced by the Vienna Circle and in 1930 or 1931 he went to Vienna, where he took part in theVienna Circle's meetings. Later he founded a new journal, ''Theoria'', published in Göteborg ; in that journal Hempel published his very first description of the paradoxes of confirmation (''Le problème de la vérité'', 1937). Eino Kaila published in 1939 a work pervaded by the principles of logical positivism (''The human knowledge'', in Finnish). He taught philosophy at the University Of Helsinki . Among his students was ''' George Henrik Von Wright ''', who published a study about logical positivism (''The Logical Empiricism'', 1943, in Finnish). Wright contributed to the development of Modal Logic and Deontic Logic . Finn ''' Jaakko Hintikka ''', who had Wright as a teacher, pursued Carnap's studies on inductive logic. Hintikka's article "A two-dimensional continuum of inductive methods" in ''Aspects of inductive logic'' (eds. J. Hintikka and P. Suppes, 1966), extended the methods Carnap used in ''The Continuum of Inductive Methods'', 1952.
- Danish philosopher very actively collaborated with neopositivists. After Hans Hahn's death in 1934, Jorgensen became an editor of the Vienna Circle's series ''Unified Science''; later he collaborated on the ''International Encyclopedia of Unified Science'', to which he contributed the 1951 essay ''The Development of Logical Empiricism''.
- English philosopher played an important role in the spread of logical positivism. His 1936 work '' Language, Truth And Logic '' gained immediate success. In that book, he completely accepted both the Verifiability Principle and the distinction between Analytic and Synthetic statements; hence he asserted that metaphysical sentences are meaningless.
- Logical positivism had extensive contacts with the group of Polish logicians who developed several branches of contemporary Logic . Polish philosophy was greatly influenced by , who studied at the University Of Vienna and taught at Lwow ; he is the founder of Polish Analytic Philosophy . He taught several Polish philosophers and logicians. Among them were:
- ---, who developed both the Algebra Of Logic and many-valued Propositional Calculus , which influenced Carnap's Inductive Logic and Reichenbach 's interpretation of Quantum Mechanics , in which Reichenbach employed a three-valued propositional calculus. He contributed to ''Erkenntnis'', the journal of logical positivism, edited by Carnap and Reichenbach.
- ---, who was interested in the logical antinomies.
- ---, who taught Philosophy Of Language , Epistemology and Logic , and contributed to ''Erkenntnis''.
- ---, who asserted that many alleged philosophical problems in fact are scientific problems, i.e. they are the object of empirical science and not of philosophy, which deals with logical and ethical problems only.
- The Polish logician , who developed the theory of Semantics in Formal Language , took part in the congresses on scientific philosophy organized by the Vienna and Berlin Circles; he greatly influenced Carnap's philosophy of language. Carnap was interested in logical Syntax but, after the publication of Tarski's works, he turned to Semantics .
Early critics of logical positivism said that its fundamental tenets could not themselves be formulated in a way that was clearly consistent. The Verifiability Criterion Of Meaning did not seem verifiable; but neither was it simply a logical Tautology , since it had implications for the practice of science and the empirical truth of other statements. This presented severe problems for the logical consistency of the theory. Another problem was that, while positive existential claims ("there is at least one human being") and negative universals ("not all ravens are black") allow for clear methods of verification (find a human or a non-black raven), negative existential claims and positive universal claims do not allow for verification.
Universal claims could apparently never be verified: How can you tell that ''all'' ravens are black, unless you've hunted down every raven ever, including those in the past and future? This led to a great deal of work on induction, probability, and "confirmation", which combined verification and falsification.
Karl Popper , a well-known critic of logical positivism, published the book ''Logik der Forschung'' ('' The Logic Of Scientific Discovery '') in 1934. In it he presented an influential alternative to the verifiability criterion of meaning, defining scientific statements in terms of Falsifiability . First, though, Popper's concern was not with distinguishing meaningful from meaningless statements, but distinguishing "scientific" from "metaphysical" statements. He did not hold that metaphysical statements must be meaningless; neither did he hold that a statement that in one century was "metaphysical" while unfalsifiable (like the ancient Greek philosophy about Atom s), could not in another century become "falsifiable" and thus "scientific". About psychoanalysis he thought something similar: in his day it offered no method for falsification, and thus was not falsifiable and not scientific. However, he did not exclude it being ''meaningful'', nor did he say psychoanalysts were necessarily "wrong" (it only couldn't be proven either way: that would have meant it was falsifiable), nor did he exclude that one day psychoanalysis could evolve into something falsifiable, and thus "scientific". He was, in general, more concerned with scientific practice than with the logical issues that troubled the positivists. Second, although Popper's philosophy of science enjoyed great popularity for some years, if his criterion is construed as an answer to the question the positivists were asking it turns out to fail in exactly parallel ways. Negative existential claims ("there are no unicorns") and positive universals ("all ravens are black") can be falsified, but positive existential and negative universal claims cannot.
Logical positivists' response to the first criticism is that logical positivism is a philosophy of science, not an Axiomatic System that can prove its own consistency (see Gödel's Incompleteness Theorem ). Secondly, a Theory Of Language and Mathematical Logic were created to answer what it really means to make statements like "all ravens are black".
A response to the second criticism was provided by , can possibly be anything more than a probable Hypothesis " (Ayer 1946:51), and therefore can only be subject to weak verification. This defence was controversial among logical positivists, some of whom stuck to strong verification, and claimed that general propositions were indeed nonsense.
Subsequent philosophy of science tends to make use of the better aspects of both of these approaches. Work by W. V. O. Quine and Thomas Kuhn has convinced many that it is not possible to provide a strict criterion for good or bad scientific method outside of the science we already have. But even this sentiment was not unknown to the logical positivists: Otto Neurath famously compared science to a boat which we must rebuild on the open sea.
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