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{{short description|Movement in Western philosophy}}
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'''Logical positivism''', later called '''logical empiricism''', and both of which together are also known as '''neopositivism''', is a movement whose central thesis is the [[verificationism|verification principle]] (also known as the verifiability criterion of meaning).<ref>{{Cite book|last=Peter Godfrey-Smith.|title=Theory and Reality : an Introduction to the Philosophy of Science.|date=2010|publisher=University of Chicago Press|isbn=978-1-282-64630-8|oclc=748357235}}</ref> This [[epistemology|theory of knowledge]] asserts that only statements verifiable through direct observation or [[deductive logic|logical proof]] are meaningful in terms of conveying [[truth]] value, information or [[fact]]ual content. Starting in the late 1920s, groups of [[philosopher]]s, [[scientist]]s, and [[mathematician]]s formed the [[Berlin Circle (philosophy)|Berlin Circle]] and the [[Vienna Circle]], which, in these two cities, would propound the ideas of logical positivism.

Flourishing in several European centres through the 1930s, the movement sought to prevent confusion rooted in unclear language and unverifiable claims by converting philosophy into "scientific philosophy", which, according to the logical positivists, ought to share the bases and structures of [[empirical sciences]]' best examples, such as [[Albert Einstein]]'s [[general theory of relativity]].<ref name=Friedman-pxiv/> Despite its ambition to overhaul philosophy by studying and mimicking the extant conduct of empirical science, logical positivism became erroneously stereotyped as a movement to regulate the scientific process and to place strict standards on it.<ref name=Friedman-pxiv/>

After [[World War II]], the movement shifted to a milder variant, logical empiricism, led mainly by [[Carl Hempel]], who, during the rise of [[Nazism]], had emigrated to the United States. In the ensuing years, the movement's central premises, still unresolved, were heavily criticised by leading philosophers, particularly [[Willard van Orman Quine]] and [[Karl Popper]], and even, within the movement itself, by Hempel. The 1962 publication of [[Thomas Kuhn]]'s landmark book ''[[The Structure of Scientific Revolutions]]'' dramatically shifted academic philosophy's focus. In 1967 philosopher [[John Passmore]] pronounced logical positivism "dead, or as dead as a philosophical movement ever becomes".<ref name=passmore>{{usurped|1=[https://web.archive.org/web/20141014040321/http://collegewing.com/logical-positivism-j-passmore-1967/ Passmore, John. 'Logical Positivism', ''The Encyclopedia of Philosophy'', Paul Edwards (ed.). New York: Macmillan, 1967, 1st edition]}}</ref>

==Origins==
Logical positivists picked from [[Tractatus Logico-Philosophicus|Ludwig Wittgenstein's early philosophy of language]] the verifiability principle or criterion of meaningfulness.  As in [[Ernst Mach]]'s [[phenomenalism]], whereby the mind knows only actual or potential sensory experience, verificationists took all sciences' basic content to be only sensory experience.  And some influence came from [[Percy Bridgman]]'s musings that others proclaimed as [[operationalism]], whereby a physical theory is understood by what laboratory procedures scientists perform to test its predictions. In [[verificationism]], only the ''verifiable'' was scientific, and thus meaningful (or ''cognitively meaningful''), whereas the unverifiable, being unscientific, were meaningless "pseudostatements" (just ''emotively meaningful'').  Unscientific discourse, as in [[ethics]] and [[metaphysics]], would be unfit for discourse by philosophers, newly tasked to organize [[knowledge]], not develop new knowledge.<ref>{{Cite web |last=HKT |date=2020-04-20 |title=Logical empiricism |url=https://sciencetheory.net/logical-empiricism/ |access-date=2024-09-19 |website=HKT Consultant }}</ref>{{citation needed|date=March 2023}}

==Definitions==
Logical positivism is sometimes stereotyped as forbidding talk of [[unobservable]]s, such as [[microscopic]] entities or such notions as causality and general principles,<ref>{{cite journal |last=Allen |first=Barry |date=May 2007 |title=Turning back the linguistic turn in the theory of knowledge |journal=[[Thesis Eleven]] |volume=89 |issue=1 |pages=6–22 (7) |doi=10.1177/0725513607076129 |s2cid=145778455 |quote=In his famous novel ''[[Nineteen Eighty-Four]]'' [[George Orwell]] gave a nice (if for us ironical) explanation of the boon Carnap expects from the logical reform of grammar. Right-thinking [[Ingsoc]] party members are as offended as Carnap by the unruliness of language. It's a scandal that grammar allows such pseudo-statements as 'It is the right of the people to alter or abolish Government' (Jefferson), or 'Das Nichts nichtet' (Heidegger). Language as it is makes no objection to such statements, and to Carnap, as to the Party, that's a sore defect. [[Newspeak]], a reformed grammar under development at the Ministry of Truth, will do what Carnap wants philosophical grammar to do}}</ref> but that is an [[strawman|exaggeration.]] Rather, most neopositivists viewed talk of unobservables as [[metaphor]]ical or elliptical: direct observations phrased abstractly or indirectly. So ''[[theoretical term]]s'' would garner meaning from ''[[observational term]]s'' via ''correspondence rules'', and thereby ''theoretical laws'' would be reduced to ''empirical laws''. Via [[Bertrand Russell]]'s [[logicism]], reducing [[mathematics]] to logic, [[physics]]' mathematical formulas would be converted to [[symbolic logic]]. Via Russell's [[logical atomism]], [[natural language|ordinary language]] would break into discrete units of meaning.<ref>{{Citation |last=Russell |first=Bertrand |title=The Philosophy of Logical Atomism [1918] |date=2024-07-03 |work=The Collected Papers of Bertrand Russell, Volume 8 |pages=157–244 |url=http://dx.doi.org/10.4324/9781003557036-20 |access-date=2024-09-19 |place=London |publisher=Routledge |isbn=978-1-003-55703-6 |last2=Slater |first2=John G.}}</ref> [[Rational reconstruction]], then, would convert ordinary statements into standardized equivalents, all networked and united by a [[logical syntax]]. A scientific theory would be stated with its method of verification, whereby a [[logical calculus]] or [[operationalism|empirical operation]] could [[deductive inference|verify]] its [[truth-value|falsity or truth]].{{citation needed|date=March 2023}}

==Development==
In the late 1930s, logical positivists fled Germany and Austria for Britain and the United States.  By then, many had replaced Mach's phenomenalism with [[Otto Neurath]]'s [[physicalism]], whereby science's content is not actual or potential sensations, but instead consists of entities that are publicly observable. [[Rudolf Carnap]], who had sparked logical positivism in the Vienna Circle, had sought to replace ''verification'' with simply ''confirmation''.  With World War II's close in 1945, logical positivism became milder, ''logical empiricism'', led largely by [[Carl Gustav Hempel|Carl Hempel]], in America, who expounded the [[covering law model]] of scientific explanation.  Logical positivism became a major underpinning of [[analytic philosophy]],<ref name="autogenerated1">See [http://plato.stanford.edu/entries/vienna-circle "Vienna Circle"] {{Webarchive|url=https://web.archive.org/web/20150810041731/http://plato.stanford.edu/entries/vienna-circle |date=10 August 2015 }} in ''Stanford Encyclopedia of Philosophy''.</ref> and dominated philosophy in the [[English-speaking world]], including [[philosophy of science]], while influencing sciences, but especially [[social science]]s, into the 1960s.  Yet the movement failed to resolve its central problems,<ref name="Smith1986">{{cite book |first=L.D. |last=Smith |year=1986 |title=Behaviorism and Logical Positivism: A Reassessment of the Alliance |publisher=Stanford University Press |isbn=978-0804713016 |lccn=85030366 |url=https://archive.org/details/behaviorismlogic0000smit |url-access=registration |page=[https://archive.org/details/behaviorismlogic0000smit/page/314 314] |quote=The secondary and historical literature on logical positivism affords substantial grounds for concluding that logical positivism failed to solve many of the central problems it generated for itself. Prominent among the unsolved problems was the failure to find an acceptable statement of the verifiability (later confirmability) criterion of meaningfulness. Until a competing tradition emerged (about the late 1950s), the problems of logical positivism continued to be attacked from within that tradition. But as the new tradition in the philosophy of science began to demonstrate its effectiveness—by dissolving and rephrasing old problems as well as by generating new ones—philosophers began to shift allegiances to the new tradition, even though that tradition has yet to receive a canonical formulation. |access-date=27 January 2016}}</ref><ref name="Bunge1996">{{cite book |first=M.A. |last=Bunge |year=1996 |title=Finding Philosophy in Social Science |publisher=Yale University Press |isbn=978-0300066067 |lccn=lc96004399 |url=https://archive.org/details/findingphilosoph0000bung |url-access=registration |page=[https://archive.org/details/findingphilosoph0000bung/page/317 317] |quote=To conclude, logical positivism was progressive compared with the classical positivism of [[Ptolemy]], [[David Hume|Hume]], [[Jean le Rond d'Alembert|d'Alembert]], [[Auguste Comte|Comte]], [[John Stuart Mill]], and [[Ernst Mach]]. It was even more so by comparison with its contemporary rivals—[[neo-Thomism]], [[neo-Kantianism]], [[intuitionism]], dialectical materialism, phenomenology, and [[existentialism]]. However, neo-positivism failed dismally to give a faithful account of science, whether natural or social. It failed because it remained anchored to sense-data and to a phenomenalist metaphysics, overrated the power of induction and underrated that of hypothesis, and denounced realism and materialism as metaphysical nonsense. Although it has never been practiced consistently in the advanced natural sciences and has been criticized by many philosophers, notably Popper (1959 [1935], 1963), logical positivism remains the tacit philosophy of many scientists. Regrettably, the anti-positivism fashionable in the metatheory of social science is often nothing but an excuse for sloppiness and wild speculation. |access-date=27 January 2016}}</ref><ref>{{cite web|url=http://www.drury.edu/ess/philsci/popper.html |title=Popper, Falsifiability, and the Failure of Positivism |date=7 August 2000 |access-date=30 June 2012 |quote=The upshot is that the positivists seem caught between insisting on the V.C. [Verifiability Criterion]—but for no defensible reason—or admitting that the V.C. requires a background language, etc., which opens the door to relativism, etc. In light of this dilemma, many folk—especially following Popper's "last-ditch" effort to "save" empiricism/positivism/realism with the falsifiability criterion—have agreed that positivism is a dead-end. |url-status=unfit |archive-url=https://web.archive.org/web/20140107230818/http://www.drury.edu/ess/philsci/popper.html |archive-date=7 January 2014 }}</ref> and its doctrines were increasingly criticized, most trenchantly by [[Willard Van Orman Quine]], [[Norwood Russell Hanson|Norwood Hanson]], [[Karl Raimund Popper|Karl Popper]], [[Thomas Samuel Kuhn|Thomas Kuhn]], and [[Carl Gustav Hempel|Carl Hempel]].{{citation needed|date=March 2023}}

==Roots==

===Language===

''[[Tractatus Logico-Philosophicus]]'', by the young [[Ludwig Wittgenstein]], introduced the view of philosophy as "critique of language", offering the possibility of a theoretically principled distinction of intelligible versus nonsensical discourse.  ''Tractatus'' adhered to a [[correspondence theory of truth]] (versus a [[coherence theory of truth]]).  Wittgenstein's influence also shows in some versions of the [[verifiability principle]].<ref>For example, compare "Proposition 4.024" of ''Tractatus'', asserting that we understand a proposition when we know the outcome if it is true, with Schlick's asserting, "To state the circumstances under which a proposition is true is the same as stating its meaning".</ref><ref>"Positivismus und realismus", ''Erkenntnis'' '''3''':1–31, English trans in Sarkar, Sahotra, ed, ''Logical Empiricism at its Peak: Schlick, Carnap, and Neurath'' (New York: Garland Publishing, 1996), p. 38.</ref> In tractarian doctrine, truths of logic are [[tautology (logic)|tautologies]], a view widely accepted by logical positivists who were also influenced by Wittgenstein's interpretation of [[probability]] although, according to Neurath, some logical positivists found ''Tractatus'' to contain too much metaphysics.<ref>For summary of the effect of Tractatus on logical positivists, see the [http://www.pitt.edu/~philosop/images/doc4-full.jpg Entwicklung der Thesen des "Wiener Kreises"] {{Webarchive|url=https://web.archive.org/web/20061109000315/http://www.pitt.edu/~philosop/images/doc4-full.jpg |date=9 November 2006 }}.</ref>

===Logicism===

[[Gottlob Frege]] began the program of reducing mathematics to logic, continued it with [[Bertrand Russell]], but lost interest in this [[logicism]], and Russell continued it with [[Alfred North Whitehead]] in their ''[[Principia Mathematica]]'', inspiring some of the more mathematical logical positivists, such as [[Hans Hahn (mathematician)|Hans Hahn]] and [[Rudolf Carnap]].<ref name=Hintikka/> Carnap's early anti-metaphysical works employed Russell's [[type theory|theory of types]].<ref>See Rudolf Carnap, "The elimination of metaphysics through logical analysis of language", ''Erkenntnis'', 1932;'''2''', reprinted in ''Logical Positivism'', Alfred Jules Ayer, ed, (New York: Free Press, 1959), pp. 60–81.</ref> Carnap envisioned a universal language that could reconstruct mathematics and thereby encode physics.<ref name=Hintikka>Jaako Hintikka, "Logicism", in Andrew D Irvine, ed, ''Philosophy of Mathematics'' (Burlington MA: North Holland, 2009),  [https://books.google.com/books?id=mbn35b2ghgkC&pg=PA283 pp. 283–84].</ref> Yet [[Kurt Gödel]]'s [[incompleteness theorem]] showed this impossible except in trivial cases, and [[Alfred Tarski]]'s [[undefinability theorem]] shattered all hopes of reducing mathematics to logic.<ref name=Hintikka/> Thus, a universal language failed to stem from Carnap's 1934 work ''Logische Syntax der Sprache'' (''Logical Syntax of Language'').<ref name=Hintikka/> Still, some logical positivists, including Carl Hempel, continued support of logicism.<ref name=Hintikka/>

===Empiricism===

In Germany, [[Hegelian metaphysics]] was a dominant movement, and Hegelian successors such as [[F H Bradley]] explained reality by postulating metaphysical entities lacking empirical basis, drawing reaction in the form of [[positivism]].<ref name="Suppe, Frederick 1999">Frederick Suppe, "The positivist model of scientific theories", in ''Scientific Inquiry'', Robert Klee, ed, (New York: Oxford University Press, 1999), pp. 16–24.</ref> Starting in the late 19th century, there was a "back to [[Kant]]" movement([[Neo-Kantianism]]).  [[Ernst Mach]]'s positivism and [[phenomenalism]] were a major influence.<ref>{{Citation |last=Ray |first=Christopher |title=Logical Positivism |date=September 2017 |url=https://onlinelibrary.wiley.com/doi/10.1002/9781405164481.ch37 |work=A Companion to the Philosophy of Science |pages=243–251 |editor-last=Newton-Smith |editor-first=W. H. |access-date=2023-10-19 |edition=1 |publisher=Wiley |doi=10.1002/9781405164481.ch37 |isbn=978-0-631-23020-5}}</ref>

==History==

===Vienna===

The [[Vienna Circle]], gathering around [[University of Vienna]] and [[Café Central]], was led principally by [[Moritz Schlick]].  Schlick had held a [[neo-Kantianism|neo-Kantian]] position, but later converted, via Carnap's 1928 book ''Der logische Aufbau der Welt'', that is, ''The Logical Structure of the World''.  A 1929 pamphlet written by [[Otto Neurath]], [[Hans Hahn (mathematician)|Hans Hahn]], and [[Rudolf Carnap]] summarized the Vienna Circle's positions.  Another member of Vienna Circle to later prove very influential was Carl Hempel.  A friendly but tenacious critic of the Circle was [[Karl Popper]], whom Neurath nicknamed the "Official Opposition".<ref>{{Cite journal |last=Bartley |first=W. W. |date=February 1982 |title=The Philosophy of Karl Popper Part III. Rationality, Criticism, and Logic |url=http://dx.doi.org/10.1007/bf02378809 |journal=Philosophia |volume=11 |issue=1-2 |pages=121–221 |doi=10.1007/bf02378809 |issn=0048-3893}}</ref>

Carnap and other Vienna Circle members, including Hahn and Neurath, saw need for a weaker criterion of meaningfulness than verifiability.<ref name=Sarkar2005/> A radical "left" wing—led by Neurath and Carnap—began the program of "liberalization of empiricism", and they also emphasized [[fallibilism]] and [[pragmatics]], which latter Carnap even suggested as empiricism's basis.<ref name=Sarkar2005/> A conservative "right" wing—led by Schlick and [[Friedrich Waismann|Waismann]]—rejected both the liberalization of empiricism and the epistemological nonfoundationalism of a move from [[phenomenalism]] to [[physicalism]].<ref name=Sarkar2005/> As Neurath and somewhat Carnap posed science toward social reform, the split in Vienna Circle also reflected political views.<ref name=Sarkar2005/>

===Berlin===

The [[Berlin Circle (philosophy)|Berlin Circle]] was led principally by [[Hans Reichenbach]].

===Rivals===

Both Moritz Schlick and Rudolf Carnap had been influenced by and sought to define logical positivism versus the neo-Kantianism of [[Ernst Cassirer]]—the then leading figure of [[Marburg school]], so called—and against [[Edmund Husserl]]'s [[phenomenology (philosophy)|phenomenology]].  Logical positivists especially opposed [[Martin Heidegger]]'s obscure metaphysics, the epitome of what logical positivism rejected.  In the early 1930s, Carnap debated Heidegger over "metaphysical pseudosentences".<ref name="Friedman-pxii">Friedman, ''Reconsidering Logical Positivism'' (Cambridge UP, 1999), [https://books.google.com/books?id=e9TjZc9wNUAC&pg=PR12 p. xii].</ref>

===Export===

As the movement's first emissary to the [[New World]], Moritz Schlick visited [[Stanford University]] in 1929, yet otherwise remained in Vienna and was murdered in 1936 at [[University of Vienna|the University]] by a former student, [[Johann Nelböck]], who was reportedly deranged.<ref name=Friedman-pxii/> That year, a British attendee at some Vienna Circle meetings since 1933, [[A. J. Ayer]] saw his ''[[Language, Truth and Logic]]'', written in English, import logical positivism to the [[English-speaking world]].  By then, the [[Nazi Party]]'s 1933 rise to power in Germany had triggered flight of intellectuals.<ref name=Friedman-pxii/> In exile in England, Otto Neurath died in 1945.<ref name=Friedman-pxii/> Rudolf Carnap, Hans Reichenbach, and Carl Hempel—Carnap's [[protégé]] who had studied in [[Berlin]] with Reichenbach—settled permanently in America.<ref name=Friedman-pxii/> Upon Germany's [[annexation of Austria]] in 1938, remaining logical positivists, many of whom were also [[Jewish]], were targeted and continued flight.  Logical positivism thus became dominant in the English-speaking world.<ref>{{Citation |title=Logical Positivism The Vienna Circle |date=2015-07-20 |work=Beyond Positivism |pages=29–36 |url=http://dx.doi.org/10.4324/9780203565520-7 |access-date=2024-09-19 |publisher=Routledge |isbn=978-0-429-23433-0}}</ref>

==Principles==

===Analytic/synthetic gap===

Concerning [[metaphysics|reality]], the [[logical truth|necessary]] is a state true in all [[possible worlds]]—mere [[logical validity]]—whereas the [[contingency (philosophy)|contingent]] hinges on the way the particular world is.  Concerning [[epistemology|knowledge]], the ''[[A priori knowledge|a priori]]'' is knowable before or without, whereas the ''[[a posteriori]]'' is knowable only after or through, relevant experience.  Concerning [[propositions|statements]], the ''[[analytic-synthetic distinction|analytic]]'' is true via terms' [[syntax|arrangement]] and [[semantics|meanings]], thus a [[tautology (logic)|tautology]]—true by logical necessity but uninformative about the world—whereas the ''[[analytic-synthetic distinction|synthetic]]'' adds reference to a state of facts, a [[contingency (philosophy)|contingency]].<ref>{{Citation |last=Rey |first=Georges |title=The Analytic/Synthetic Distinction |date=2023 |url=https://plato.stanford.edu/archives/spr2023/entries/analytic-synthetic/ |encyclopedia=The Stanford Encyclopedia of Philosophy |editor-last=Zalta |editor-first=Edward N. |access-date=2023-07-10 |edition=Spring 2023 |publisher=Metaphysics Research Lab, Stanford University |editor2-last=Nodelman |editor2-first=Uri}}</ref><ref>{{Cite web |title=Quine, Willard Van Orman: Analytic/Synthetic Distinction {{!}} Internet Encyclopedia of Philosophy |url=https://iep.utm.edu/quine-an/ |access-date=2023-07-10 }}</ref>

In 1739, [[David Hume]] cast [[Hume's fork|a fork]] aggressively dividing "relations of ideas" from "matters of fact and real existence", such that all truths are of one type or the other.<ref name=Flew>{{cite book|author=Antony Flew|title=A Dictionary of Philosophy: Revised Second Edition|url=https://books.google.com/books?id=MmJHVU9Rv3YC&pg=PA156|edition=2nd|year=1984|publisher=St. Martin's Press|location=New York|isbn=978-0-312-20923-0|page=156}}</ref><ref>{{cite book|author=Helen Buss Mitchell|title=Roots of Wisdom: A Tapestry of Philosophical Traditions|url=https://books.google.com/books?id=P6o0OUzwmSAC&pg=PA249|year=2010|publisher=Cengage Learning|isbn=978-0-495-80896-1|pages=249–50}}</ref> By Hume's fork, truths by relations among ideas (abstract) all align on one side (analytic, necessary, ''a priori''), whereas truths by states of actualities (concrete) always align on the other side (synthetic, contingent, ''a posteriori'').<ref name=Flew/> Of any treatises containing neither, Hume orders, "Commit it then to the flames, for it can contain nothing but [[sophistry]] and illusion".<ref name=Flew/>

Thus awakened from "dogmatic slumber", [[Immanuel Kant]] quested to answer Hume's challenge—but by explaining how metaphysics is possible.  Eventually, in his [[Critique of Pure Reason|1781 work]], Kant crossed the tines of Hume's fork to identify another range of truths by necessity—[[synthetic a priori|synthetic ''a priori'']], statements claiming states of facts but known true before experience—by arriving at [[transcendental idealism]], attributing the mind a constructive role in [[phenomena]] by arranging [[sense data]] into the very experience ''space'', ''time'', and ''substance''.  Thus, Kant saved [[Newton's law of universal gravitation]] from Hume's [[problem of induction]] by finding uniformity of nature to be ''a priori'' knowledge.  Logical positivists rejected Kant's [[synthetic a priori|synthetic ''a priori'']], and adopted [[Hume's fork]], whereby a statement is either analytic and ''a priori'' (thus [[logical truth|necessary]] and verifiable logically) or synthetic and ''[[a posteriori]]'' (thus [[Contingency (philosophy)|contingent]] and verifiable empirically).<ref name=Flew/>

===Observation/theory gap===

Early, most logical positivists proposed that all knowledge is based on logical inference from simple "protocol sentences" grounded in observable facts.  In the 1936 and 1937 papers "Testability and meaning", individual terms replace sentences as the units of meaning.<ref name=Sarkar2005/> Further, theoretical terms no longer need to acquire meaning by explicit definition from observational terms: the connection may be indirect, through a system of implicit definitions.<ref name=Sarkar2005/> Carnap also provided an important, pioneering discussion of disposition predicates.<ref name=Sarkar2005/>

===Cognitive meaningfulness===

====Verification====

The logical positivists' initial stance was that a statement is "cognitively meaningful" in terms of conveying truth value, information or factual content only if some finite procedure conclusively determines its truth.<ref>For a classic survey of other versions of verificationism, see Carl G Hempel, "Problems and changes in the empiricist criterion of meaning", ''Revue Internationale de Philosophie'', 1950;'''41''':41–63.</ref> By this [[verifiability principle]], only statements verifiable either by their [[analytic proposition|analyticity]] or by empiricism were ''cognitively meaningful''.  [[Metaphysics]], [[ontology]], as well as much of [[ethics]] failed this criterion, and so were found ''cognitively meaningless''.  Moritz Schlick, however, did not view ethical or [[aesthetics|aesthetic]] statements as [[meaning (philosophy of language)|cognitively meaningless]].<ref>See Moritz Schlick, "[https://books.google.com/books?id=LTOaM0X6e6cC&q=%22The+future+of+philosophy%22 The future Of philosophy]", in ''The Linguistic Turn'', Richard Rorty, ed, (Chicago: University of Chicago Press, 1992), pp. 43–53.</ref>  ''Cognitive meaningfulness'' was variously defined: having a [[truth value]]; corresponding to a possible state of affairs; intelligible or understandable as are scientific statements.<ref>Examples of these different views can be found in Scheffler's ''Anatomy of Inquiry'', Ayer's ''Language, Truth, and Logic'', Schlick's "Positivism and realism" (reprinted in Sarkar 1996 and Ayer 1959), and Carnap's ''Philosophy and Logical Syntax''.</ref>

Ethics and aesthetics were subjective preferences, while [[theology]] and other metaphysics contained "pseudostatements", neither true nor false.  This meaningfulness was cognitive, although other types of meaningfulness—for instance, emotive, expressive, or figurative—occurred in metaphysical discourse, dismissed from further review.  Thus, logical positivism indirectly asserted [[Hume's law]], the principle that ''is'' statements cannot justify ''ought'' statements, but are separated by an unbridgeable gap.  [[A. J. Ayer]]'s 1936 book asserted an extreme variant—the [[emotivism|boo/hooray doctrine]]—whereby all evaluative judgments are but emotional reactions.<ref name=":0">{{Cite book |last=Ayer |first=A.J |title=Language, Truth, and Meaning |year=1936 |pages=2 (Preface to the 1st edition) and 63-77 (Chapter 6) }}</ref><ref>{{Cite web |title=24.231 Ethics – Handout 3 Ayer's Emotivism |url=https://ocw.mit.edu/courses/24-231-ethics-fall-2009/f5b666a0f7be491b8e44180c6d7629fc_MIT24_231F09_lec04.pdf}}</ref>

====Confirmation<!--'Basic statement', 'Observation statement', 'Protocol statement' redirect here-->====

In an important pair of papers in 1936 and 1937, "Testability and meaning", Carnap replaced ''verification'' with ''confirmation'', on the view that although universal laws cannot be verified they can be confirmed.<ref name=Sarkar2005/> Later, Carnap employed abundant logical and mathematical methods in researching inductive logic while seeking to provide an account of probability as "degree of confirmation", but was never able to formulate a model.<ref name=IEP-Carnap>Mauro Murzi [http://www.iep.utm.edu/carnap "Rudolf Carnap (1891–1970)"] {{Webarchive|url=https://web.archive.org/web/20131014232341/http://www.iep.utm.edu/carnap/ |date=14 October 2013 }}, ''Internet Encyclopedia of Philosophy'', 12 April 2001.</ref> In Carnap's inductive logic, every universal law's degree of confirmation is always zero.<ref name=IEP-Carnap/> In any event, the precise formulation of what came to be called the "criterion of cognitive significance" took three decades (Hempel 1950, Carnap 1956, Carnap 1961).<ref name=Sarkar2005/>

Carl Hempel became a major critic within the logical positivism movement.<ref name="sep-hempel">{{cite encyclopedia |first=James |last=Fetzer |editor=Edward N. Zalta |year=2012 |title=Carl Hempel |encyclopedia=The Stanford Encyclopedia of Philosophy |edition=Summer 2012 |url=http://plato.stanford.edu/entries/hempel/#SciRea |quote=It would fall to Hempel to become perhaps the most astute critic of that movement and to contribute to its refinement as logical empiricism... Hempel himself attained a certain degree of prominence as a critic of this movement... The analytic/synthetic distinction and the observational/theoretical distinction were tied together by the ''verifiability criterion of meaningfulness''... By this standard, sentences that are non-analytic but also non-verifiable, including various theological or metaphysical assertions concerning God or The Absolute, qualify as cognitively meaningless. This was viewed as a desirable result. But, as Hempel would demonstrate, its scope was far too sweeping, since it also rendered meaningless the distinctively scientific assertions made by laws and theories... The analytic/synthetic distinction took a decided hit when the noted logician, Willard van Orman Quine, published "Two Dogmas of Empiricism" (1953), challenging its adequacy... While the analytic/synthetic distinction appears to be justifiable in modeling important properties of languages, the observational/theoretical distinction does not fare equally well. Within logical positivism, observation language was assumed to consist of names and predicates whose applicability or not can be ascertained, under suitable conditions, by means of direct observation...  Karl Popper (1965, 1968), however, would carry the argument in a different direction by looking at the ontic nature of properties... Hempel (1950, 1951), meanwhile, demonstrated that the verifiability criterion could not be sustained. Since it restricts empirical knowledge to observation sentences and their deductive consequences, scientific theories are reduced to logical constructions from observables. In a series of studies about cognitive significance and empirical testability, he demonstrated that the verifiability criterion implies that existential generalizations are meaningful, but that universal generalizations are not, even though they include general laws, the principal objects of scientific discovery. Hypotheses about relative frequencies in finite sequences are meaningful, but hypotheses concerning limits in infinite sequences are not. The verifiability criterion thus imposed a standard that was too strong to accommodate the characteristic claims of science and was not justifiable... Both theoretical and dispositional predicates, which refer to non-observables, posed serious problems for the positivist position, since the verifiability criterion implies they must be reducible to observables or are empirically meaningless... The need to dismantle the verifiability criterion of meaningfulness together with the demise of the observational/theoretical distinction meant that logical positivism no longer represented a rationally defensible position. At least two of its defining tenets had been shown to be without merit. Since most philosophers believed that Quine had shown the analytic/synthetic distinction was also untenable, moreover, many concluded that the enterprise had been a total failure. Among the important benefits of Hempel's critique, however, was the production of more general and flexible criteria of cognitive significance... Hempel suggested multiple criteria for assessing the cognitive significance of different theoretical systems, where significance is not categorical but rather a matter of degree... The elegance of Hempel's study laid to rest any lingering aspirations for simple criteria of cognitive significance and signaled the demise of logical positivism as a philosophical movement. Precisely what remained, however, was in doubt. Presumably, anyone who rejected one or more of the three principles defining positivism—the analytic/synthetic distinction, the observational/theoretical distinction, and the verifiability criterion of significance—was not a logical positivist. The precise outlines of its philosophical successor, which would be known as "logical empiricism", were not entirely evident. Perhaps this study came the closest to defining its intellectual core. Those who accepted Hempel's four criteria and viewed cognitive significance as a matter of degree were members, at least in spirit. But some new problems were beginning to surface with respect to Hempel's covering-law explication of explanation and old problems remained from his studies of induction, the most remarkable of which was known as "the paradox of confirmation". |access-date=31 August 2012 |archive-url=https://web.archive.org/web/20120930055402/http://plato.stanford.edu/entries/hempel/#SciRea |archive-date=30 September 2012 |url-status=live}}</ref> Hempel criticized the positivist thesis that empirical knowledge is restricted to ''Basissätze''/''Beobachtungssätze''/''Protokollsätze'' ('''basic statements'''<!--boldface per WP:R#PLA--> or '''observation statements'''<!--boldface per WP:R#PLA--> or '''protocol statements'''<!--boldface per WP:R#PLA-->).<ref name="sep-hempel"/> Hempel elucidated the [[paradox of the ravens|paradox of confirmation]].<ref>{{Citation |last=Crupi |first=Vincenzo |title=Confirmation |date=2021 |url=https://plato.stanford.edu/archives/spr2021/entries/confirmation/ |encyclopedia=The Stanford Encyclopedia of Philosophy |editor-last=Zalta |editor-first=Edward N. |access-date=2023-07-10 |edition=Spring 2021 |publisher=Metaphysics Research Lab, Stanford University}}</ref>

====Weak verification====

The second edition of [[A. J. Ayer]]'s book arrived in 1946, and discerned ''strong'' versus ''weak'' forms of verification.  Ayer concluded, "A proposition is said to be verifiable, in the strong sense of the term, if, and only if, its truth could be conclusively established by experience", but is verifiable in the weak sense "if it is possible for experience to render it probable".<ref name=Ayer-p50>Ayer, ''[[Language, Truth and Logic]]'', 1946, pp. 50–51.</ref> And yet, "no proposition, other than a [[Tautology (logic)|tautology]], can possibly be anything more than a probable [[hypothesis]]".<ref name=Ayer-p50/> Thus, all are open to weak verification.<ref name=":0" />

==Philosophy of science==

Upon the global defeat of Nazism, and the removal from philosophy of rivals for radical reform—[[Marburg school|Marburg]] neo-Kantianism, [[Edmund Husserl|Husserlian]] phenomenology, [[Martin Heidegger|Heidegger]]'s "existential hermeneutics"—and while hosted in the climate of American [[pragmatism]] and commonsense empiricism, the neopositivists shed much of their earlier, revolutionary zeal.<ref name=Friedman-pxiv/>  No longer crusading to revise traditional philosophy into a new ''scientific philosophy'', they became respectable members of a new philosophy subdiscipline, ''[[philosophy of science]]''.<ref name=Friedman-pxiv>Michael Friedman, ''[https://books.google.com/books?id=e9TjZc9wNUAC Reconsidering Logical Positivism] '' (New York: Cambridge University Press, 1999), [https://books.google.com/books?id=e9TjZc9wNUAC&pg=PR14 p. xiv].</ref>  Receiving support from [[Ernest Nagel]], logical empiricists were especially influential in the social sciences.<ref name=Novick-p546>Novick, ''That Noble Dream'' (Cambridge UP, 1988), [https://books.google.com/books?id=mhiw__MLyVAC&dq=Carnap+Hempel+Nagel+social+sciences+natural+fact+value&pg=PA546 p. 546].</ref>

===Explanation===

[[positivism|Comtean positivism]] had viewed science as ''description'', whereas the logical positivists posed science as ''explanation'', perhaps to better realize the envisioned [[unity of science]] by covering not only [[fundamental science]]—that is, [[fundamental interactions|fundamental physics]]—but the [[special science]]s, too, for instance [[biology]], [[anthropology]], [[psychology]], [[sociology]], and [[economics]].<ref name=Woodward-Background>James Woodward, [http://plato.stanford.edu/archives/win2011/entries/scientific-explanation "Scientific explanation"] {{Webarchive|url=https://web.archive.org/web/20131202051319/http://plato.stanford.edu/archives/win2011/entries/scientific-explanation/ |date=2 December 2013 }} – sec 1 "Background and introduction", in Zalta EN, ed,''The Stanford Encyclopedia of Philosophy'', Winter 2011 edn</ref> The most widely accepted concept of scientific explanation, held even by neopositivist critic Karl Popper, was the [[deductive-nomological model]] (DN model).<ref name=Woodward-introduction>James Woodward, [http://plato.stanford.edu/archives/win2011/entries/scientific-explanation "Scientific explanation"] {{Webarchive|url=https://web.archive.org/web/20131202051319/http://plato.stanford.edu/archives/win2011/entries/scientific-explanation/ |date=2 December 2013 }} – Article overview, Zalta EN, ed, ''The Stanford Encyclopedia of Philosophy'', Winter 2011 edn</ref> Yet DN model received its greatest explication by Carl Hempel, first in his 1942 article "The function of general laws in history", and more explicitly with [[Paul Oppenheim]] in their 1948 article "Studies in the logic of explanation".<ref name=Woodward-introduction/>

In the DN model, the stated phenomenon to be explained is the ''explanandum''—which can be an event, [[scientific law|law]], or [[scientific theory|theory]]—whereas premises stated to explain it are the ''explanans''.<ref name=Suppe>Suppe, ''Structure of Scientific Theories'' (U Illinois P, 1977), [https://books.google.com/books?id=SpvZsxCA0TIC&pg=PA619 pp. 619–21].</ref>  Explanans must be true or highly confirmed, contain at least one law, and entail the explanandum.<ref name=Suppe/>   Thus, given initial conditions ''C''<sub>1</sub>, ''C''<sub>2</sub>, ..., ''C''<sub>n</sub>'' plus general laws ''L''<sub>1</sub>, ''L''<sub>2</sub>, ..., ''L<sub>n</sub>'', event ''E'' is a deductive consequence and scientifically explained.<ref name=Suppe/>  In the DN model, a law is an unrestricted generalization by conditional proposition—''If A, then B''—and has empirical content testable.<ref>Eleonora  Montuschi, ''Objects in Social Science'' (London & New York: Continuum, 2003), [https://books.google.com/books?id=bQ24-BV8WSAC&pg=PA62 pp. 61–62].</ref>  (Differing from a merely true regularity—for instance, ''George always carries only $1 bills in his wallet''—a law suggests what ''must'' be true,<ref>Bechtel, ''Philosophy of Science'' (Lawrence Erlbaum, 1988), p. 25.</ref> and is consequent of a [[scientific theory]]'s [[axiom]]atic structure.<ref>Bechtel, ''Philosophy of Science'' (Lawrence Erlbaum, 1988), pp. 27–28.</ref>)

By the [[Humeanism#Causality and necessity|Humean]] empiricist view that humans observe sequences of events, (not cause and effect, as causality and causal mechanisms are unobservable), the DN model neglects causality beyond mere [[constant conjunction]], first event ''A'' and then always event ''B''.<ref name=Woodward-Background/>  Hempel's explication of the DN model held [[natural laws]]—empirically confirmed regularities—as satisfactory and, if formulated realistically, approximating causal explanation.<ref name=Suppe/>  In later articles, Hempel defended the DN model and proposed a probabilistic explanation, inductive-statistical model (IS model).<ref name=Suppe/> the DN and IS models together form the ''covering law model'',<ref name=Suppe/> as named by a critic, [[William Dray]].<ref>Georg Henrik von Wright, ''Explanation and Understanding'' (Ithaca NY: Cornell University Press, 1971), [https://books.google.com/books?id=33wCi2bg5x0C&pg=PA11 p. 11].</ref>  Derivation of statistical laws from other statistical laws goes to deductive-statistical model (DS model).<ref name=Glennan>Stuart Glennan, [https://books.google.com/books?id=od68ge7aF6wC&pg=PA276 p. 276], in Sarkar S & Pfeifer J, eds, ''The Philosophy of Science: An Encyclopedia'', Volume 1: A–M (New York: Routledge, 2006).</ref>  [[Georg Henrik von Wright]], another critic, named it ''subsumption theory'',<ref name=Riedel>Manfred Riedel, [https://books.google.com/books?id=It3ji_AuO3sC&dq=Covering+subsumption&pg=PA3 pp. 3–4], in Manninen J & Tuomela R, eds, ''Essays on Explanation and Understanding: Studies in the Foundation of Humanities and Social Sciences'' (Dordrecht: D Reidel Publishing, 1976).</ref> fitting the ambition of theory reduction.{{citation needed|date=March 2023}}

===Unity of science===

Logical positivists were generally committed to "[[Unified Science]]", and sought a common language or, in Neurath's phrase, a "universal slang" whereby all scientific propositions could be expressed.<ref>For a review of "unity of science" to, see Gregory Frost-Arnold, [http://philsci-archive.pitt.edu/archive/00002005/01/PSA2004Short.rtf "The large-scale structure of logical empiricism: Unity of science and the rejection of metaphysics"] {{Webarchive|url=https://web.archive.org/web/20070623031008/http://philsci-archive.pitt.edu/archive/00002005/01/PSA2004Short.rtf |date=23 June 2007 }}.</ref> The adequacy of proposals or fragments of proposals for such a language was often asserted on the basis of various "reductions" or "explications" of the terms of one special science to the terms of another, putatively more fundamental. Sometimes these reductions consisted of set-theoretic manipulations of a few logically primitive concepts (as in Carnap's ''Logical Structure of the World'', 1928).<ref>{{Citation |last=Hinst |first=Peter |title=Carnap, Rudolf: Der logische Aufbau der Welt |date=2020 |work=Kindlers Literatur Lexikon (KLL) |pages=1–2 |url=http://dx.doi.org/10.1007/978-3-476-05728-0_9509-1 |access-date=2024-09-19 |place=Stuttgart |publisher=J.B. Metzler |isbn=978-3-476-05728-0}}</ref>  Sometimes, these reductions consisted of allegedly analytic or ''a priori'' deductive relationships (as in Carnap's "Testability and meaning").<ref>{{Citation |last=Sarkar |first=Sahotra |title=Rudolf Carnap Testability and Meaning |date=2021-11-12 |work=Logical Empiricism at its Peak |pages=200–265 |url=http://dx.doi.org/10.4324/9781003249573-13 |access-date=2024-09-19 |place=New York |publisher=Routledge |isbn=978-1-003-24957-3}}</ref> A number of publications over a period of thirty years would attempt to elucidate this concept.

===Theory reduction===

As in [[positivism|Comtean positivism]]'s envisioned [[unity of science]], neopositivists aimed to network all special sciences through the [[covering law model|covering law model of scientific explanation]].  And ultimately, by supplying [[boundary condition]]s and supplying bridge laws within the covering law model, all the special sciences' laws would reduce to [[fundamental interactions|fundamental physics]], the [[fundamental science]].<ref>{{Cite book |last=Kuhn |first=Thomas S. |url=http://dx.doi.org/10.7208/chicago/9780226458106.001.0001 |title=The Structure of Scientific Revolutions |date=1996 |publisher=University of Chicago Press |isbn=978-0-226-45808-3}}</ref>

==Critics==

After World War II, key tenets of logical positivism, including its atomistic philosophy of science, the verifiability principle, and the [[Hume's law|fact/value gap]], drew escalated criticism.<ref name=Sarkar2005>{{cite book |first1=S |last1=Sarkar |first2=J |last2=Pfeifer |year=2005 |title=The Philosophy of Science: An Encyclopedia |volume=1 |publisher=Taylor & Francis |isbn=978-0415939270 |url=https://books.google.com/books?id=od68ge7aF6wC&pg=PA83 |page=83}}</ref> The verifiability criterion made [[universal proposition|universal statement]]s 'cognitively' meaningless, and even made statements beyond empiricism for technological but not conceptual reasons meaningless, which was taken to pose significant problems for the philosophy of science.<ref name="sep-hempel"/><ref name="sep-problem-of-induction">{{cite encyclopedia |author=John Vicker |editor=Edward N Zalta |year=2011 |title=The problem of induction |encyclopedia=The Stanford Encyclopedia of Philosophy |edition=Fall 2011 |url=http://plato.stanford.edu/archives/fall2011/entries/induction-problem/#VerCon |quote=This initial formulation of the criterion was soon seen to be too strong; it counted as meaningless not only metaphysical statements but also statements that are clearly empirically meaningful, such as that all copper conducts electricity and, indeed, any universally quantified statement of infinite scope, as well as statements that were at the time beyond the reach of experience for technical, and not conceptual, reasons, such as that there are mountains on the back side of the moon. These difficulties led to modification of the criterion: The latter to allow empirical verification if not in fact then at least in principle, the former to soften verification to empirical confirmation. |access-date=24 August 2012 |archive-url=https://web.archive.org/web/20131202064021/http://plato.stanford.edu/archives/fall2011/entries/induction-problem/#VerCon |archive-date=2 December 2013 |url-status=live}}</ref><ref name="sep-vienna-circle">{{cite encyclopedia |first=Thomas |last=Uebel |editor=Edward N. Zalta |year=2008 |title=Vienna Circle |encyclopedia=The Stanford Encyclopedia of Philosophy |edition=Fall 2008 |url=http://plato.stanford.edu/archives/fall2008/entries/vienna-circle/ |quote=<p>What Carnap later called the 'liberalization of empiricism' was underway and different camps became discernible within the Circle&nbsp;... In the first place, this liberalization meant the accommodation of universally quantified statements and the return, as it were, to salient aspects of Carnap's 1928 conception. Everybody had noted that the Wittgensteinian verificationist criterion rendered universally quantified statements meaningless. Schlick (1931) thus followed Wittgenstein's own suggestion to treat them instead as representing rules for the formation of verifiable singular statements. (His abandonment of conclusive verifiability is indicated only in Schlick 1936a.) A second element that began to do so soon was the recognition of the problem of the irreducibility of disposition terms to observation terms&nbsp;... A third element was that disagreement arose as to whether the in-principle verifiability or support turned on what was merely logically possible or on what was nomologically possible, as a matter of physical law etc. A fourth element, finally, was that differences emerged as to whether the criterion of significance was to apply to all languages or whether it was to apply primarily to constructed, formal languages. Schlick retained the focus on logical possibility and natural languages throughout, but Carnap had firmly settled his focus on nomological possibility and constructed languages by the mid-thirties. Concerned with natural language, Schlick (1932, 1936a) deemed all statements meaningful for which it was logically possible to conceive of a procedure of verification; concerned with constructed languages only, Carnap (1936–37) deemed meaningful only statements for whom it was nomologically possible to conceive of a procedure of confirmation or disconfirmation.</p><p>Many of these issues were openly discussed at the Paris congress in 1935. Already in 1932 Carnap had sought to sharpen his previous criterion by stipulating that those statements were meaningful that were syntactically well-formed and whose non-logical terms were reducible to terms occurring in the basic observational evidence statements of science. While Carnap's focus on the reduction of descriptive terms allows for the conclusive verification of some statements, his criterion also allowed universally quantified statements to be meaningful, provided they were syntactically and terminologically correct (1932a, §2). It was not until one of his Paris addresses, however, that Carnap officially declared the meaning criterion to be mere confirmability. Carnap's new criterion required neither verification nor falsification but only partial testability so as now to include not only universal statements but also the disposition statements of science&nbsp;... Though plausible initially, the device of introducing non-observational terms in this way gave rise to a number of difficulties which impugned the supposedly clear distinctions between logical and empirical matters and analytic and synthetic statements (Hempel 1951). Independently, Carnap himself (1939) soon gave up the hope that all theoretical terms of science could be related to an observational base by such reduction chains. This admission raised a serious problem for the formulation of a meaning criterion: how was one to rule out unwanted metaphysical claims while admitting as significant highly abstract scientific claims?</p> |access-date=22 August 2012 |archive-url=https://web.archive.org/web/20131202074112/http://plato.stanford.edu/archives/fall2008/entries/vienna-circle/ |archive-date=2 December 2013 |url-status=live}}{{long quote|date=November 2020}}</ref> These problems were recognized within the movement, which hosted attempted solutions—Carnap's move to ''confirmation'', Ayer's acceptance of ''weak verification''—but the program drew sustained criticism from a number of directions by the 1950s. Even philosophers disagreeing among themselves on which direction general [[epistemology]] ought to take, as well as on [[philosophy of science]], agreed that the logical empiricist program was untenable, and it became viewed as self-contradictory: the verifiability criterion of meaning was itself unverified.<ref name=Putnam1985>{{cite book |author=Hilary Putnam |year=1985 |title=Philosophical Papers: Volume 3, Realism and Reason |publisher=Cambridge University Press |isbn=978-0521313940 |lccn=lc82012903}}</ref>  Notable critics included  [[Karl Raimund Popper|Popper]], [[Willard Van Orman Quine|Quine]], [[Norwood Russell Hanson|Hanson]], [[Thomas Samuel Kuhn|Kuhn]], [[Hilary Putnam|Putnam]], [[J. L. Austin|Austin]], [[Peter Strawson|Strawson]], [[Nelson Goodman|Goodman]], and [[Richard Rorty|Rorty]].{{citation needed|date=March 2023}}

===Popper===
An early, tenacious critic was [[Karl Popper]] whose 1934 book ''Logik der Forschung'', arriving in English in 1959 as ''[[The Logic of Scientific Discovery]]'', directly answered verificationism. Popper considered the [[problem of induction]] as rendering empirical verification logically impossible,<ref>Popper then denies that science requires [[inductive inference]] or that it actually exists, although most philosophers believe it exists and that science requires it [Samir Okasha, ''The Philosophy of Science: A Very Short Introduction'' (New York: [[Oxford University Press]], 2002), p. 23],</ref> and the [[deductive fallacy]] of [[affirming the consequent]] reveals any phenomenon's capacity to host more than one logically possible explanation.  Accepting [[scientific method]] as [[hypothetico-deductive model|hypotheticodeduction]], whose [[argument form|inference form]] is [[denying the consequent]], Popper finds scientific method unable to proceed without [[falsifiable]] predictions.<ref name="Popper">{{Cite journal |last=Popper |first=Karl |date=2005-11-04 |title=The Logic of Scientific Discovery |url=http://dx.doi.org/10.4324/9780203994627 |doi=10.4324/9780203994627}}</ref> Popper thus identifies [[falsifiability]] to [[problem of demarcation|demarcate]] not ''meaningful'' from ''meaningless'' but simply ''scientific'' from  ''unscientific''—a label not in itself unfavorable.<ref name="Popper"/>

Popper finds virtue in metaphysics, required to develop new scientific theories. And an unfalsifiable—thus unscientific, perhaps metaphysical—concept in one era can later, through evolving knowledge or technology, become falsifiable, thus scientific.  Popper also found science's quest for truth to rest on values. Popper disparages the ''[[pseudoscientific]]'', which occurs when an unscientific theory is proclaimed true and coupled with seemingly scientific method by "testing" the unfalsifiable theory—whose predictions are confirmed by necessity—or when a scientific theory's falsifiable predictions are strongly falsified but the theory is persistently protected by "immunizing stratagems", such as the appendage of ''[[ad hoc]]'' clauses saving the theory or the recourse to increasingly speculative hypotheses shielding the theory.<ref name=":1">{{Cite journal |last=Popper |first=Karl |date=2014-05-01 |title=Conjectures and Refutations |url=http://dx.doi.org/10.4324/9780203538074 |doi=10.4324/9780203538074}}</ref>

Explicitly denying the positivist view of meaning and verification, Popper developed the epistemology of [[critical rationalism]], which considers that human knowledge evolves by conjectures and refutations, and that no number, degree, and variety of empirical successes can either verify or confirm scientific theory. For Popper, science's aim is ''corroboration'' of scientific theory, which strives for [[scientific realism]] but accepts the maximal status of strongly corroborated [[verisimilitude]] ("truthlikeness"). Popper thus acknowledged the value of the positivist movement's emphasis on science but claimed that he had "killed positivism".<ref name=":1" />{{citation needed|date=March 2023}}

===Quine===

Although an empiricist, American logician [[Willard Van Orman Quine]] published the 1951 paper "[[Two Dogmas of Empiricism]]",<ref name=":2">W. V. O. Quine, "Two Dogmas of Empiricism", ''Philosophical Review'' 1951;'''60''':20–43, collected in Quine, ''From a Logical Point of View'' (Cambridge, Massachusetts: Harvard University Press, 1953).</ref> which challenged conventional empiricist presumptions.  Quine attacked the [[analytic-synthetic distinction|analytic/synthetic division]], which the verificationist program had been hinged upon in order to entail, by consequence of [[Hume's fork]], both [[logical truth|necessity]] and [[A priori and a posteriori|aprioricity]]. Quine's [[ontological relativity]] explained that every term in any statement has its meaning contingent on a vast network of knowledge and belief, the speaker's conception of the entire world. Quine later proposed [[naturalized epistemology]].<ref name=":2" />

===Hanson===

In 1958, [[Norwood Russell Hanson|Norwood Hanson]]'s ''Patterns of Discovery'' undermined the division of [[observation]] versus [[theory]],<ref name=Novick-p527>Novick, ''That Noble Dream'' (Cambridge University Press, 1988), [https://books.google.com/books?id=mhiw__MLyVAC&dq=Hanson&pg=PA527 p. 527].</ref> as one can predict, collect, prioritize, and assess data only via some horizon of expectation set by a theory.  Thus, any [[dataset]]—the direct observations, the scientific facts—is [[theory-laden|laden with theory]].<ref>{{Cite journal |last=Hanson |first=Norwood Russell |date=1967-06-08 |title=An Anatomy of Discovery |url=http://dx.doi.org/10.2307/2024301 |journal=The Journal of Philosophy |volume=64 |issue=11 |pages=321 |doi=10.2307/2024301 |issn=0022-362X}}</ref>

===Kuhn===

With his landmark ''[[The Structure of Scientific Revolutions]]'' (1962), [[Thomas Samuel Kuhn|Thomas Kuhn]] critically destabilized the verificationist program, which was presumed to call for [[foundationalism]].<ref>{{Cite journal |last=Daston |first=Lorraine |date=2020-05-01 |title=Thomas S. Kuhn, The Structure of Scientific Revolutions (1962) |url=http://dx.doi.org/10.1215/08992363-8090152 |journal=Public Culture |volume=32 |issue=2 |pages=405–413 |doi=10.1215/08992363-8090152 |issn=0899-2363}}</ref> (But already in the 1930s, [[Otto Neurath]] had argued for nonfoundationalism via [[coherentism]] by likening science to a boat ([[Neurath's boat]]) that scientists must rebuild at sea.<ref name=ONPSP>{{cite book|title=Otto Neurath: Philosophy Between Science and Politics|volume=38|series=Ideas in Context|first1=Nancy|last1=Cartwright|author-link1=Nancy Cartwright (philosopher) |first2=Jordi|last2=Cat|first3=Lola|last3=Fleck|first4=Thomas E.|last4=Uebel|publisher=Cambridge UP|year=2008|isbn=978-0521041119|chapter=On Neurath's Boat|pages=89–94}}</ref>) Although Kuhn's thesis itself was attacked even by opponents of neopositivism, in the 1970 postscript to ''Structure'', Kuhn asserted, at least, that there was no [[algorithm]] to science—and, on that, even most of Kuhn's critics agreed.{{citation needed|date=March 2023}}

Powerful and persuasive, Kuhn's book, unlike the vocabulary and symbols of logic's [[formal language]], was written in [[natural language]] open to the layperson.<ref name=Novick-p526/> Kuhn's book was first published in a volume of ''[[International Encyclopedia of Unified Science]]''—a project begun by logical positivists but {{nowrap|co-edited}} by Neurath whose view of science was already nonfoundationalist as mentioned above—and some sense unified science, indeed, but by bringing it into the realm of historical and social assessment, rather than fitting it to the model of physics.<ref name=Novick-p526/> Kuhn's ideas were rapidly adopted by scholars in disciplines well outside natural sciences,<ref name=Novick-p526>Novick, ''That Noble Dream'' (Cambridge University Press, 1988), [https://books.google.com/books?id=mhiw__MLyVAC&dq=Kuhn's+logical+Unified&pg=PA526 pp. 526–27] {{Webarchive|url=https://web.archive.org/web/20161125032543/https://books.google.com/books?id=mhiw__MLyVAC&pg=PA526&dq=Kuhn's+logical+Unified |date=25 November 2016 }}.</ref> and, as logical empiricists were extremely influential in the social sciences,<ref name=Novick-p546/> ushered academia into [[postpositivism]] or postempiricism.<ref name=Novick-p526/>

===Putnam===

The "[[Received view of theories|received view]]" operates on the ''correspondence rule'' that states, "The observational terms are taken as referring to specified phenomena or phenomenal properties, and the only interpretation given to the theoretical terms is their explicit definition provided by the correspondence rules".<ref name="Suppe, Frederick 1999"/> According to [[Hilary Putnam]], a former student of [[Hans Reichenbach|Reichenbach]] and of [[Rudolf Carnap|Carnap]], the dichotomy of observational terms versus theoretical terms introduced a problem within scientific discussion that was nonexistent until this dichotomy was stated by logical positivists.<ref>Hilary Putnam, "Problems with the observational/theoretical distinction", in ''Scientific Inquiry,'' Robert Klee, ed (New York: Oxford University Press, 1999), pp. 25–29.</ref> Putnam's four objections:

* Something is referred to as "observational" if it is observable directly with our senses. Then an observational term cannot be applied to something unobservable. If this is the case, there are no observational terms.
* With Carnap's classification, some unobservable terms are not even theoretical and belong to neither observational terms nor theoretical terms. Some theoretical terms refer primarily to observational terms.
* Reports of observational terms frequently contain theoretical terms.
* A scientific theory may not contain any theoretical terms (an example of this is [[Charles Darwin|Darwin]]'s [[Darwinian evolution|original theory of evolution]]).

Putnam also alleged that positivism was actually a form of [[idealism|metaphysical idealism]] by its rejecting scientific theory's ability to garner knowledge about nature's unobservable aspects.  With his "no miracles" argument, posed in 1974, Putnam asserted [[scientific realism]], the stance that science achieves true—or approximately true—knowledge of the world as it exists independently of humans' sensory experience. In this, Putnam opposed not only the positivism but other [[instrumentalism]]—whereby scientific theory is but a human tool to predict human observations—filling the void left by positivism's decline.<ref name="Friedman-pxii" />

==Decline==

By the late 1960s, logical positivism had become exhausted.<ref name="Fotionarticle">{{cite book |author=[[Nick Fotion|Nicholas G Fotion]] |editor=Ted Honderich |title=The Oxford Companion to Philosophy |publisher=Oxford University Press |location=Oxford |year=1995 |page=[https://archive.org/details/oxfordcompaniont00hond/page/508 508] |isbn=978-0-19-866132-0 |url=https://archive.org/details/oxfordcompaniont00hond/page/508 }}</ref> In 1976, [[A. J. Ayer]] quipped that "the most important" defect of logical positivism "was that nearly all of it was false," though he maintained "it was true in spirit."<ref name=Routledge/><ref>{{cite web |url=https://www.youtube.com/watch?v=4cnRJGs08hE | archive-url=https://ghostarchive.org/varchive/youtube/20211109/4cnRJGs08hE| archive-date=2021-11-09 | url-status=live|title=Ayer on Logical Positivism: Section 4 |website=[[YouTube]] |at=6:30}}{{cbignore}}</ref> Although logical positivism tends to be recalled as a pillar of [[scientism]],<ref name=Stahl-etal-p180>{{cite book|author1=William Stahl|author2=Robert A. Campbell|author3=Gary Diver|author4=Yvonne Petry|title=Webs of Reality: Social Perspectives on Science and Religion|url=https://books.google.com/books?id=GY6i84rSKMcC&pg=PA180|year=2002|publisher=Rutgers University Press|isbn=978-0-8135-3107-6|page=180}}</ref> [[Carl Hempel]] was key in establishing the subdiscipline of the philosophy of science,<ref name="Friedman-pxii"/> where [[Thomas Kuhn]] and [[Karl Popper]] brought in the era of [[postpositivism]].<ref name=Novick-p526/> [[John Passmore]] found logical positivism to be "dead, or as dead as a philosophical movement ever becomes".<ref name=Routledge>{{cite book|last=Hanfling|first=Oswald|chapter=Logical Positivism|title=Routledge History of Philosophy|year=2003|publisher=Routledge|pages=193f}}</ref>

Logical positivism's fall reopened the debate over the metaphysical merit of scientific theory, whether it can offer knowledge of the world beyond human experience (scientific realism) versus whether it is but a human tool to predict human experience (instrumentalism).<ref>Hilary Putnam, "What is realism?", in Jarrett Leplin, ed, ''Scientific Realism'' (Berkeley, Los Angeles, London: University of California Press, 1984), [https://books.google.com/books?id=zhBeVFm8WuAC&dq=Realism+realists+positivism+opera-tionalism&pg=PA140 p. 140].</ref><ref>Ruth Lane, [https://dx.doi.org/10.1177/0951692896008003003 "Positivism, scientific realism and political science: Recent developments in the philosophy of science"], ''Journal of Theoretical Politics'', 1996 Jul'''8'''(3):361–82, abstract.</ref> Philosophers increasingly critiqued logical positivism, often misrepresenting it without thorough examination.<ref name=Friedman-p1>Friedman, ''Reconsidering Logical Positivism'' (Cambridge, 1999), [https://books.google.com/books?id=e9TjZc9wNUAC&dq=half+centry+bogeyman+faults+failings+dispassionate&pg=PA1 p. 1].</ref><ref name=Friedman-p2/> It was generally reduced to oversimplifications and stereotypes, particularly associating it with [[foundationalism]].<ref name=Friedman-p2>Friedman, ''Reconsidering Logical Positivism'' (Cambridge, 1999), [https://books.google.com/books?id=e9TjZc9wNUAC&dq=clear+critics+agendas+foundationalism&pg=PA2 p. 2].</ref> The movement helped anchor [[analytic philosophy]] in the English-speaking world and reintroducing empiricism in Britain. Its influence extended beyond philosophy, particularly in psychology and social sciences.<ref name=Friedman-pxii/>

==See also==
{{cols}}

* {{Annotated link |Anti-realism}}
* {{Annotated link |Definitions of philosophy}}
* {{Annotated link |Empirio-criticism}}
* {{Annotated link |Raven paradox}}
* {{Annotated link |Sociological positivism}}
* {{Annotated link |Strategic positivism}}
*''[[The Structure of Science]]''
* {{Annotated link |Unobservable}}
{{colend}}

===People===

* {{Annotated link |Gustav Bergmann}}
* {{Annotated link |Herbert Feigl}}
* {{Annotated link |Kurt Grelling}}
* {{Annotated link |Friedrich Waismann}}
* {{Annotated link |R. B. Braithwaite}}

==Notes==
{{Reflist}}

==References==
*Bechtel, William, ''[https://content.taylorfrancis.com/books/download?dac=C2007-0-02715-3&isbn=9781317767480&format=googlePreviewPdf Philosophy of Science: An Overview for Cognitive Science]'' (Hillsdale NJ: Lawrence Erlbaum Assoc, 1988).
*Friedman, Michael, ''[https://books.google.com/books?id=e9TjZc9wNUAC Reconsidering Logical Positivism]'' (New York: Cambridge University Press, 1999).
*Novick, Peter, ''[https://archive.org/details/isbn_9780521357456 <!-- quote=positivism. --> That Noble Dream: The 'Objectivity Question' and the American Historical Profession]'' (Cambridge UK: Cambridge University Press, 1988).
*Stahl, William A  & Robert A Campbell, Yvonne Petry, Gary Diver, ''[https://books.google.com/books?id=GY6i84rSKMcC&q=%22logical+positivism%22 Webs of Reality: Social Perspectives on Science and Religion]'' (Piscataway NJ: Rutgers University Press, 2002).
*Suppe, Frederick, ed, ''[https://books.google.com/books?id=SpvZsxCA0TIC&q=positivism The Structure of Scientific Theories]'', 2nd edn (Urbana IL: University of Illinois Press, 1977).

==Further reading==
{{refbegin}}
*[[Peter Achinstein|Achinstein, Peter]] and [[Stephen Francis Barker|Barker, Stephen F.]] ''The Legacy of Logical Positivism: Studies in the Philosophy of Science''. Baltimore: Johns Hopkins Press, 1969.
*Ayer, Alfred Jules. ''Logical Positivism''. Glencoe, Ill: Free Press, 1959.
*Barone, Francesco. ''Il neopositivismo logico''. Roma Bari: Laterza, 1986.
*Bergmann, Gustav. ''The Metaphysics of Logical Positivism''. New York: Longmans Green, 1954.
*Cirera, Ramon. ''[https://archive.org/details/carnapviennacir00cire/page/n18 <!-- pg=1 quote=positivism. --> Carnap and the Vienna Circle: Empiricism and Logical Syntax]''. Atlanta, GA: Rodopi, 1994.
*Edmonds, David & Eidinow, John; ''Wittgenstein's Poker'', {{ISBN|0-06-621244-8}}
*Friedman, Michael. ''Reconsidering Logical Positivism''. Cambridge, UK: Cambridge University Press, 1999
*Gadol, Eugene T. ''Rationality and Science: A Memorial Volume for Moritz Schlick in Celebration of the Centennial of his Birth''. Wien: Springer, 1982.
*Geymonat, Ludovico. ''La nuova filosofia della natura in Germania''. Torino, 1934.
*Giere, Ronald N. and Richardson, Alan W. ''[https://books.google.com/books?id=Xa9LuLMrJvkC&q=positivism Origins of Logical Empiricism]''. Minneapolis: University of Minnesota Press, 1997.
*[[Oswald Hanfling|Hanfling, Oswald]]. ''Logical Positivism''. Oxford: B. Blackwell, 1981.
*[[Jim Holt (philosopher)|Holt, Jim]], "Positive Thinking" (review of [[Karl Sigmund]], ''Exact Thinking in Demented Times:  The Vienna Circle and the Epic Quest for the Foundations of Science'', Basic Books, 449 pp.), ''[[The New York Review of Books]]'', vol. LXIV, no. 20 (21 December 2017), pp.&nbsp;74–76.
*Jangam, R. T. ''Logical Positivism and Politics''. Delhi: Sterling Publishers, 1970.
*Janik, Allan and [[Stephen Toulmin|Toulmin, Stephen]]. ''Wittgenstein's Vienna''. London: Weidenfeld and Nicolson, 1973.
*Kraft, Victor. The Vienna Circle: ''The Origin of Neo-positivism, a Chapter in the History of Recent Philosophy''. New York: Greenwood Press, 1953.
*McGuinness, Brian. ''Wittgenstein and the Vienna Circle: Conversations Recorded by Friedrich Waismann''. Trans. by Joachim Schulte and Brian McGuinness. New York: Barnes & Noble Books, 1979.
* Milkov, Nikolay (ed.). ''Die Berliner Gruppe. Texte zum Logischen Empirismus von Walter Dubislav, Kurt Grelling, Carl G. Hempel, Alexander Herzberg, Kurt Lewin, Paul Oppenheim und Hans Reichenbach.'' Hamburg: Meiner 2015. (German)
*Mises von, Richard. ''Positivism: A Study in Human Understanding''. Cambridge: Harvard University Press, 1951.
*Parrini, Paolo. ''Empirismo logico e convenzionalismo: saggio di storia della filosofia della scienza''. Milano: F. Angeli, 1983.
*Parrini, Paolo; Salmon, Wesley C.; Salmon, Merrilee H. (ed.) ''Logical Empiricism&nbsp;– Historical and Contemporary Perspectives'', Pittsburgh: University of Pittsburgh Press, 2003.
*Reisch, George. ''How the Cold War Transformed Philosophy of Science : To the Icy Slopes of Logic''. New York: Cambridge University Press, 2005.
*Rescher, Nicholas. ''The Heritage of Logical Positivism''. Lanham, MD: University Press of America, 1985.
*Richardson, Alan and Thomas Uebel (eds.) ''The Cambridge Companion to Logical Positivism.'' New York: Cambridge University Press, 2007.
*Salmon, Wesley and Wolters, Gereon (ed.) ''Logic, Language, and the Structure of Scientific Theories: Proceedings of the Carnap-Reichenbach Centennial, University of Konstanz, 21–24 May 1991'', Pittsburgh: University of Pittsburgh Press, 1994.
*Sarkar, Sahotra (ed.) ''[https://books.google.com/books?id=eS8jeSgy8eIC&q=positivism The Emergence of Logical Empiricism: From 1900 to the Vienna Circle]''. New York: Garland Publishing, 1996.
*Sarkar, Sahotra (ed.) ''[https://books.google.com/books?id=hf0Ar62uA34C&q=positivism Logical Empiricism at its Peak: Schlick, Carnap, and Neurath]''. New York: Garland Pub., 1996.
*Sarkar, Sahotra (ed.) ''[https://books.google.com/books?id=H-OdzRfpehEC&q=positivism Logical Empiricism and the Special Sciences]: Reichenbach, Feigl, and Nagel''. New York: Garland Pub., 1996.
*Sarkar, Sahotra (ed.) ''[https://books.google.com/books?id=NiQBRoKrVW0C&q=positivism Decline and Obsolescence of Logical Empiricism: Carnap vs. Quine and the Critics]''. New York: Garland Pub., 1996.
*Sarkar, Sahotra (ed.) ''[https://books.google.com/books?id=FJ68n_9XXAwC&q=positivism The Legacy of the Vienna Circle: Modern Reappraisals]''. New York: Garland Pub., 1996.
*Spohn, Wolfgang (ed.) ''[https://books.google.com/books?id=ED3sCAAAQBAJ&q=positivism Erkenntnis Orientated: A Centennial Volume for Rudolf Carnap and Hans Reichenbach]'', Boston: Kluwer Academic Publishers, 1991.
*Stadler, Friedrich. ''[https://books.google.com/books?id=2rAlCQAAQBAJ&q=positivism The Vienna Circle. Studies in the Origins, Development, and Influence of Logical Empiricism].'' New York: Springer, 2001. – 2nd Edition: Dordrecht: Springer, 2015.
*Stadler, Friedrich (ed.). ''The Vienna Circle and Logical Empiricism. Re-evaluation and Future Perspectives.'' Dordrecht – Boston – London, Kluwer 2003.
*{{cite journal
  |last=Werkmeister
  |first=William
  |title=Seven Theses of Logical Positivism Critically Examined
  | journal = The Philosophical Review
  | volume = 46
  | issue = 3
  |pages=276–297
  |date=May 1937
  | doi = 10.2307/2181086
  |jstor=2181086
  }}
{{refend}}

==External links==
*{{Commons category-inline}}
'''Articles by logical positivists'''
* [https://sites.google.com/site/gnadav/TheScientificConceptionoftheWorldeng.doc The Scientific Conception of the World: The Vienna Circle]
* [http://www.calstatela.edu/dept/phil/pdf/res/Carnap-Elimination-of-Metaphysics.pdf Carnap, Rudolf. 'The Elimination of Metaphysics Through Logical Analysis of Language']
* [http://www.ditext.com/carnap/carnap.html Carnap, Rudolf. 'Empiricism, Semantics, and Ontology.']
* [https://web.archive.org/web/20051215185548/http://philosophy.ru/edu/ref/sci/carnap.html Excerpt from Carnap, Rudolf. ''Philosophy and Logical Syntax''.]
* [https://web.archive.org/web/20110511191629/http://etext.lib.virginia.edu/cgi-local/DHI/dhicontrib2.cgi?id=dv3-69 Feigl, Herbert. 'Positivism in the Twentieth Century (Logical Empiricism)', ''Dictionary of the History of Ideas'', 1974, Gale Group (Electronic Edition)]
* [https://web.archive.org/web/20060615004555/http://www.lawrence.edu/fast/boardmaw/Hempel_Emp_Crit.html Hempel, Carl. 'Problems and Changes in the Empiricist Criterion of Meaning.']

'''Articles on logical positivism'''
* {{cite SEP |url-id=logical-empiricism/ |title=Logical Empiricism |last=Creath |first=Richard}}
* [http://www.philosophypages.com/hy/6q.htm Kemerling, Garth. 'Logical Positivism', ''Philosophy Pages'']
* [http://www.murzim.net/Articles/Positivism.pdf Murzi, Mauro. 'Logical Positivism', ''The New Encyclopedia of Unbelief'', Tom Flynn (ed.). Prometheus Books, 2007 (PDF version)]
* [http://murzim.net/LP/LP00.html Murzi, Mauro. 'The Philosophy of Logical Positivism.']
* {{usurped|1=[https://web.archive.org/web/20141014040321/http://collegewing.com/logical-positivism-j-passmore-1967/ Passmore, John. 'Logical Positivism', ''The Encyclopedia of Philosophy'', Paul Edwards (ed.). New York: Macmillan, 1967, first edition]}}

'''Articles on related philosophical topics'''
* [http://plato.stanford.edu/archives/sum2003/entries/probability-interpret/ Hájek, Alan. 'Interpretations of Probability', ''The Stanford Encyclopedia of Philosophy (Summer 2003 Edition), Edward N. Zalta (ed.)'']
* [http://plato.stanford.edu/archives/fall2003/entries/analytic-synthetic/ Rey, Georges. 'The Analytic/Synthetic Distinction', ''The Stanford Encyclopedia of Philosophy (Fall 2003 Edition)'', Edward N. Zalta (ed.)]
* [http://plato.stanford.edu/archives/win2001/entries/genrel-early/ Ryckman, Thomas A., 'Early Philosophical Interpretations of General Relativity', ''The Stanford Encyclopedia of Philosophy (Winter 2001 Edition), Edward N. Zalta (ed.)'']
* [http://plato.stanford.edu/archives/sum2003/entries/lvov-warsaw/ Woleński, Jan. 'Lvov-Warsaw School', ''The Stanford Encyclopedia of Philosophy (Summer 2003 Edition), Edward N. Zalta (ed.)'']
* [http://plato.stanford.edu/archives/sum2003/entries/scientific-explanation/ Woodward, James. 'Scientific Explanation', ''The Stanford Encyclopedia of Philosophy (Summer 2003 Edition), Edward N. Zalta (ed.)'']

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