Editing Logical positivism

{{short description|Movement in Western philosophy}}
{{Use dmy dates|date=March 2020}}
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'''Logical positivism''', also known as '''logical empiricism''' or '''neo-positivism''', was a philosophical movement, in the [[empiricism|empiricist]] tradition, that sought to formulate a [[naturalized epistemology|scientific philosophy]] in which philosophical discourse would be, in the perception of its proponents, as authoritative and meaningful as [[empirical science]].<ref name=Friedman-pxiv>{{cite book |first=Michael |last=Friedman |year=1999 |title=Reconsidering Logical Positivism |publisher=Cambridge University Press |lccn=85030366|page=xiv}}</ref>

Logical positivism's central thesis was the [[verificationism|verification principle]], also known as the "verifiability criterion of meaning", according to which a statement is ''cognitively meaningful'' only if it can be verified through [[observation|empirical observation]] or if it is a [[tautology (logic)|tautology]] (true by virtue of its own [[semantics|meaning]] or its own [[syntax|logical form]]).<ref>{{cite book|last=Godfrey-Smith |first=Peter |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> The verifiability criterion thus rejected statements of [[metaphysics]], [[theology]], [[ethics]] and [[aesthetics]] as ''cognitively meaningless'' in terms of [[truth value]] or [[fact|factual]] content. Despite its ambition to overhaul philosophy by mimicking the structure and process of empirical science, logical positivism became erroneously stereotyped as an agenda to regulate the scientific process and to place strict standards on it.<ref name=Friedman-pxiv/>

The movement emerged in the late 1920s among [[philosopher]]s, [[scientist]]s and [[mathematician]]s congregated within the [[Vienna Circle]] and [[Berlin Circle (philosophy)|Berlin Circle]] and flourished in several European centres through the 1930s. By the end of [[World War II]], many of its members had settled in the [[anglosphere|English-speaking world]] and the project shifted to less radical goals within the [[philosophy of science]].<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=Spring 2024 |url=https://plato.stanford.edu/entries/vienna-circle/ |access-date=27 February 2025}}</ref>

By the 1950s, problems identified within logical positivism's central tenets became seen as intractable, drawing escalating criticism among leading philosophers, notably from [[Willard van Orman Quine]] and [[Karl Popper]], and even from within the movement, from [[Carl Hempel]]. These problems would remain unresolved, precipitating the movement's eventual decline and abandonment by the 1960s. In 1967, philosopher [[John Passmore]] pronounced logical positivism "dead, or as dead as a philosophical movement ever becomes".<ref name=hanfling />

==Origins==

Logical positivism emerged in [[Germany]] and [[Austria]] amid a cultural background characterised by the dominance of [[Hegelian metaphysics]] and the work of Hegelian successors such as [[F. H. Bradley]], whose [[metaphysics]] portrayed the world without reference to [[observation|empirical observation]].<ref name="Suppe2">{{cite book |title=Scientific Inquiry |editor=Robert Klee |last=Suppe |first=Frederick |chapter=The Positivist Model of Scientific Theories |pages=16-24 |year=1999 |publisher=Oxford University Press}}</ref> The late 19th century also saw the emergence of [[neo-Kantianism]] as a philosophical movement, in the [[Rationalism|rationalist]] tradition.<ref name=uebel3>{{harvnb|Uebel|2008}} 3.7</ref>

The logical positivist program established its theoretical foundations in the [[empiricism]] of [[David Hume]], [[Auguste Comte]] and [[Ernst Mach]], along with the [[positivism]] of Comte and Mach, defining its exemplar of science in [[Albert Einstein|Einstein]]'s [[general theory of relativity]].<ref>{{cite book |title=A Dictionary of Philosophy |last=Flew|first=Antony G|page=156 |chapter=Science: Conjectures and refutations |year=1984|publisher=St Martin's Press|location=New York|editor= Andrew Bailey}}</ref><ref name=uebel3/> In accordance with Mach's [[phenomenalism]], whereby [[material object]]s exist only as [[sense data|sensory stimuli]] rather than as observable entities in the [[reality|real world]], logical positivists took all scientific knowledge to be only sensory experience.<ref>{{cite book |last=Ray |first=Christopher |chapter=Logical Positivism |date=September 2017 |url=https://onlinelibrary.wiley.com/doi/10.1002/9781405164481.ch37 |title=A Companion to the Philosophy of Science |pages=243–251 |editor-last=Newton-Smith |editor-first=W. H. |access-date=2023-10-19 |edition=1st |publisher=Wiley |doi=10.1002/9781405164481.ch37 |isbn=978-0-631-23020-5}}</ref> Further influence came from [[Percy Bridgman]]'s [[operationalism]]—whereby a concept is not knowable unless it can be measured experimentally—as well as [[Immanuel Kant]]'s perspectives on [[a priori|aprioricity]].<ref>{{cite journal |title=The Myth of Operationism |first=Thomas H. |last=Leahey |journal=The Journal of Mind and Behavior |volume=1 |issue=2 |year=1980 |pages=127-143}}</ref><ref name=uebel3/>

[[Ludwig Wittgenstein]]'s ''[[Tractatus Logico-Philosophicus]]'' established the theoretical foundations for the [[verifiability principle]].<ref> ''Tractatus''  Proposition 4.024 bears resemblance to Schlick's statement, "To state the circumstances under which a proposition is true is the same as stating its meaning".</ref><ref>{{cite journal |last=Schlick |first=Moritz |year=1932 |title=Positivismus und realismus |journal=Erkenntnis |volume=3 |issue=1 |pages=1-31 |doi=10.1007/BF01886406}} English translation in: {{cite book |title=Logical Empiricism at its Peak: Schlick, Carnap, and Neurath |editor-last=Sarkar |editor-first=Sahotra |page=38 |year=1996 |location=New York |publisher=Garland Publishing}}</ref> His work introduced the view of philosophy as "critique of language", discussing theoretical distinctions between intelligible and nonsensical discourse. ''Tractatus'' adhered to a [[correspondence theory of truth]], as opposed to a [[coherence theory of truth]]. Logical positivists were also influenced by Wittgenstein's interpretation of [[probability]] though, according to [[Otto Neurath|Neurath]], some objected to the metaphysics in ''Tractatus''.<ref>{{cite book |last=Rand |first=Rose |title=Entwicklung der Thesen des "Wiener Kreises" |year=1933}}</ref>

==History==

===Vienna and Berlin Circles===

{{Main|Vienna Circle}}

The [[Vienna Circle]] was led principally by [[Moritz Schlick]], congregating around the [[University of Vienna]] and at the [[Café Central]]. A manifesto written by [[Otto Neurath]], [[Hans Hahn (mathematician)|Hans Hahn]] and [[Rudolf Carnap]] in 1929 summarised the Vienna Circle's positions. Schlick had originally held a [[neo-Kantianism|neo-Kantian]] position, but later converted, via Carnap's 1928 book ''Der logische Aufbau der Welt'' (''The Logical Structure of the World''). The Viennese maintained closely cooperative ties with the [[Berlin Circle]], among whom [[Hans Reichenbach]] was pre-eminent. [[Carl Hempel]], who studied under Reichenbach in Germany, was also to prove influential in the movement's later history.<ref name="sep-hempel"/> A friendly but tenacious critic of the movement was [[Karl Popper]], whom Neurath nicknamed the "Official Opposition".<ref>{{cite journal |last=Bartley |first=W. W. |year=1982 |title=The Philosophy of Karl Popper Part III. Rationality, Criticism, and Logic |journal=Philosophia |volume=11 |issue=1-2 |pages=121–221 |doi=10.1007/bf02378809 |issn=0048-3893}}</ref>

Early in the movement, Carnap, Hahn, Neurath and others recognised that the [[logical positivist#Verifiability Criterion of Meaning|verifiability criterion]] was too stringent in that it rejected [[universal generalization|universal statements]], which are vital to [[hypothesis|scientific hypothesis]].<ref name=Sarkar2005/> A radical ''left wing'' emerged from the Vienna Circle, led by Neurath and Carnap, who proposed revisions to weaken the criterion, a program they referred to as the "liberalisation of empiricism". A conservative ''right wing'', led by Schlick and [[Friedrich Waismann|Waismann]], instead sought to classify universal statements as analytic truths, thereby to reconcile them with the existing criterion.<ref>{{harvnb|Uebel|2008}} 3.1</ref> Within the liberal wing Carnap emphasised [[fallibilism]], as well as [[pragmatics]], which he considered integral to [[empiricism]]. Neurath prescribed a move from [[Ernst Mach|Mach]]'s [[phenomenalism]] to [[physicalism]], though this would be opposed by Schlick. As Neurath and Carnap sought to pose science toward social reform, the split in the Vienna Circle also reflected political differences.<ref name=Sarkar2005/>

Both Schlick and Carnap had been influenced by and sought to define logical positivism versus the neo-Kantianism of [[Ernst Cassirer]], the contemporary leading figure of the [[Marburg school]], and against [[Edmund Husserl]]'s [[phenomenology (philosophy)|phenomenology]]. Logical positivists especially opposed [[Martin Heidegger]]'s obscure metaphysics, the epitome of what they had rejected through their epistemological doctrines. In the early 1930s, Carnap debated Heidegger over "metaphysical pseudosentences".<ref name=Friedman-pxii>{{harvnb|Friedman|1999}} p. xii</ref>

===Anglosphere===

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. J. Ayer]], a British attendee at various Vienna Circle meetings since 1933, published ''[[Language, Truth and Logic]]'', which imported logical positivism to the [[English-speaking world]]. In 1933, the [[Nazi Party]]'s rise to power in Germany had triggered flight of intellectuals, which accelerated upon Germany's [[annexation of Austria]] in 1938.<ref name=Friedman-pxii/> The logical positivists, many of whom were [[Jewish]], were targeted and continued flight throughout the pre-war period. Their philosophy thus became dominant in the [[English-speaking world]].<ref>{{cite book |chapter=Logical Positivism The Vienna Circle |first=Bruce |last=Caldwell |year=1984 |title=Beyond Positivism |pages=29–36 |doi=10.4324/9780203565520-7 |publisher=Routledge |isbn=978-0-429-23433-0}}</ref>

By the late 1930s, many in the movement had replaced [[phenomenalism]] with Neurath's [[physicalism]], whereby [[material object]]s are not reducible to [[Stimulus (physiology)|sensory stimuli]] but exist as publicly observable entities in the [[reality|real world]]. Neurath settled in England, where he died in 1945. Carnap, Reichenbach and Hempel settled permanently in America.<ref name=Friedman-pxii/>

===Post-war period===

Following the [[World War 2|Second World War]], logical positivism—now referred to by some as ''logical empiricism''—turned to less radical objectives in the [[philosophy of science]]. Led by [[Carl Gustav Hempel|Carl Hempel]], who expounded the [[covering law model]] of [[scientific explanation]], the movement became a major underpinning of [[analytic philosophy]] in the English-speaking world<ref>{{harvnb|Uebel|2008}} 2.1</ref> and its influence extended beyond philosophy into the [[social science]]s. At the same time, the movement drew intensifying scrutiny over 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 |page=314}}</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 |page=317 |quote=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|sense-data]] and to a [[phenomenalism|phenomenalist]] metaphysics, overrated the power of [[inductive reasoning|induction]] and underrated that of [[hypothesis]], and denounced [[philosophical realism|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, 1963), logical positivism remains the tacit philosophy of many scientists.}}</ref> and its doctrines were increasingly criticised, 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]].<ref name=sep-vienna-circle/>

==Principles==

===Verification and Confirmation===

{{Main|Verificationism}}

====Verifiability Criterion of Meaning====

According to the [[verificationism|verifiability criterion of meaning]], a statement is ''cognitively meaningful'' only if it is either verifiable by [[observation|empirical observation]] or is an [[analytic proposition|analytic truth]] (i.e. true by virtue of its own [[semantics|meaning]] or its own [[syntax|logical form]]).<ref>{{cite journal |last=Hempel |first=Carl G |title=Problems and changes in the empiricist criterion of meaning |journal=Revue Internationale de Philosophie |year=1950 |volume=41 |pages=41–63}}</ref> ''[[meaning (philosophy of language)|Cognitive meaningfulness]]'' was defined variably: possessing [[truth value]]; or corresponding to a possible state of affairs; or intelligible or understandable as are scientific statements. Other types of meaning—for instance, emotive, expressive or figurative—were dismissed from further review.<ref>Various different views are discussed in Ayer's ''Language, Truth, and Logic'', Schlick's "Positivism and realism" (reprinted in {{harvnb|Sarkar|1996}} and {{harvnb|Ayer|1959}}) and Carnap's ''Philosophy and Logical Syntax''.</ref>

[[Metaphysics]], [[theology]], as well as much of [[ethics]] and [[aesthetics]] failed this criterion, and so were found cognitively meaningless and only ''emotively meaningful'' (though, notably, Schlick considered ethical and aesthetic statements cognitively meaningful).<ref>{{cite journal |last=Allen |first=Barry |year=2007 |title=Turning back the linguistic turn in the theory of knowledge |journal=[[Thesis Eleven]] |volume=89 |issue=1 |pages=6–22 |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' ([[Thomas Jefferson|Jefferson]]), or 'Das Nichts nichtet' ([[Martin Heidegger|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><ref>{{cite book |last=Schlick |first=Moritz |url=https://books.google.com/books?id=LTOaM0X6e6cC&q=%22The+future+of+philosophy%22 |chapter=The future Of philosophy |title=The Linguistic Turn |editor=Richard Rorty |location=Chicago |publisher=University of Chicago Press |year=1992 |pages=43–53}}</ref> Ethics and aesthetics were considered subjective preferences, while theology and metaphysics contained "pseudostatements" that were neither true nor false. Thus, logical positivism indirectly asserted [[Hume's law]], the principle that [[fact|factual]] statements cannot justify [[axiology|evaluative]] statements, and that the two are separated by an unbridgeable gap. [[A. J. Ayer]]'s ''[[Language, Truth and Logic]]'' (1936) presented an extreme version of this principle—the [[emotivism|boo/hooray doctrine]]—whereby all evaluative judgments are merely emotional reactions.<ref name=Ayer1>{{cite book |last=Ayer |first=A.J |title=Language, Truth, and Meaning |year=1936 |pages=2,63-77}}</ref>

====Revisions to the criterion====

Logical positivists in the Vienna Circle recognised quickly that the verifiability criterion was too restrictive.<ref name=sep-hempel/> Specifically, [[universal generalization|universal statement]]s were noted to be empirically unverifiable, rendering vital domains of science and [[reason]], such as [[hypothesis|scientific hypothesis]], ''cognitively meaningless'' under verificationism. This would pose significant problems for the logical positivist program, absent revisions to its criterion of meaning.<ref>{{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=https://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 [[universal generalization|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. |access-date=24 August 2012}}</ref>

In his 1936 and 1937 papers, ''Testability and Meaning'', [[Rudolf Carnap|Carnap]] proposed ''confirmation'' in place of verification, determining that, though universal laws cannot be verified, they can be confirmed.<ref name=Sarkar2005/> Carnap employed abundant logical and mathematical tools to research an [[inductive reasoning|inductive logic]] that would account for probability according to ''degrees of confirmation''. However, he was never able to formulate a model. In Carnap's inductive logic, a universal law's degree of confirmation was always zero.<ref name=IEP-Carnap>{{cite encyclopedia |last=Murzi |first=Mauro |url=https://www.iep.utm.edu/carnap |title=Rudolf Carnap (1891–1970) |encyclopedia=Internet Encyclopedia of Philosophy |year=2001}}</ref> The formulation of what eventually came to be called the "criterion of cognitive significance", stemming from this research, took three decades (Hempel 1950, Carnap 1956, Carnap 1961).<ref name=Sarkar2005/> [[Carl Hempel]], who became a prominent critic of the logical positivist movement, elucidated the [[paradox of the ravens|paradox of confirmation]].<ref>{{cite encyclopedia |last=Crupi |first=Vincenzo |title=Confirmation |year=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}}</ref>

In his 1936 book, ''Language, Truth and Logic'', [[A. J. Ayer]] distinguished ''strong'' and ''weak'' verification. He stipulated that, "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". He would add that, "no proposition, other than a [[Tautology (logic)|tautology]], can possibly be anything more than a probable [[hypothesis]]". Thus, he would conclude that all are open to weak verification.<ref>{{harvnb|Ayer|1936}} pp. 50–51</ref>

===Analytic-synthetic distinction===

{{Main|Analytic-synthetic distinction}}

In [[justification (epistemology)|theories of justification]], ''[[A priori knowledge|a priori]]'' statements are those that can be known independently of [[observation]], contrasting with ''[[a posteriori]]'' statements, which are dependent on observation. Statements may also be categorised into ''[[analytic-synthetic distinction|analytic]]'' and ''[[analytic-synthetic distinction|synthetic]]'': Analytic statements are true by virtue of their own [[semantics|meaning]] or their own [[syntax|logical form]], therefore are [[tautology (logic)|tautologies]] that are true by [[logical truth|necessity]] but uninformative about the world. Synthetic statements, in comparison, are [[contingency (philosophy)|contingent]] propositions that refer to a state of facts concerning the world.<ref>{{cite encyclopedia |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 encyclopedia |title=Quine, Willard Van Orman: Analytic/Synthetic Distinction |encyclopedia=Internet Encyclopedia of Philosophy |url=https://iep.utm.edu/quine-an/ |access-date=2023-07-10}}</ref>

[[David Hume]] proposed an unambiguous distinction between analytic and synthetic, categorising knowledge exclusively as either "relations of ideas" (which are ''a priori'', analytic and [[abstract and concrete|abstract]]) or "matters of fact and real existence" (''a posteriori'', synthetic and [[abstract and concrete|concrete]]), a classification referred to as [[Hume's fork]].<ref name=Flew>{{cite book |last=Flew |first=Antony |title=A Dictionary of Philosophy |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 |last=Mitchell |first=Helen Buss |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> [[Immanuel Kant]] identified a further category of knowledge: [[synthetic a priori|Synthetic ''a priori'']] statements, which are informative about the world, but known without observation. This principle is encapsulated in Kant's [[transcendental idealism]], which attributes the mind a constructive role in [[phenomena]] whereby [[Rationalism#Intuition-deduction thesis|intuitive]] truths—including synthetic ''a priori'' conceptions of [[space]] and [[time]]—function as an interpretative filter for an observer's experience of the world.<ref>{{cite encyclopedia |last=Rohlf |first=Michael |title=Immanuel Kant |year=2010 |url=https://plato.stanford.edu/entries/kant/#TraIde |encyclopedia=The Stanford Encyclopedia of Philosophy |editor-last=Zalta |editor-first=Edward N. |access-date=2025-02-02 |edition=Summer 2024 |publisher=Metaphysics Research Lab, Stanford University}}</ref> His thesis would serve to rescue [[Newton's law of universal gravitation]] from Hume's [[problem of induction]] by determining [[uniformitarianism|uniformity of nature]] to be in the category of ''a priori'' knowledge.<ref>{{cite encyclopedia |last1=De Pierris |first1=Graciela |last2=Friedman |first2=Michael |title=Kant and Hume on Causality |year=2008 |url=https://plato.stanford.edu/entries/kant-hume-causality/ |encyclopedia=The Stanford Encyclopedia of Philosophy |editor-last=Zalta |editor-first=Edward N. |access-date=2025-02-02 |edition=Summer 2024 |publisher=Metaphysics Research Lab, Stanford University}}</ref>

The Vienna Circle rejected Kant's conception of synthetic ''a priori'' knowledge given its incompatibility with the [[verificationism|verifiability criterion]].<ref>{{harvnb|Uebel|2008}} 2.3</ref> Yet, they adopted the Kantian position of defining mathematics and logic—ordinarily considered synthetic truths—as ''a priori''.<ref>{{cite book |title=Early Analytic Philosophy: Frege, Russell, Wittgenstein |editor1=William W. Tait |editor2=Leonard Linsky |editor2-link=Leonard Linsky |author=Michael Friedman |chapter=Carnap and Wittgenstein's ''Tractatus'' |page=29 |chapter-url=https://books.google.com/books?id=eNA_TdDTNkMC&pg=PA29 |isbn=978-0812693447 |year=1997 |publisher=Open Court Publishing}}</ref> [[Rudolf Carnap|Carnap]]'s solution to this discrepancy would be to reinterpret logical truths as tautologies, redefining logic as analytic, building upon theoretical foundations established in [[Ludwig Wittgenstein|Wittgenstein]]'s ''Tractatus''. Mathematics, in turn, would be reduced to logic through the [[Logical Positivism#Logicism|logicist approach]] proposed by [[Gottlob Frege]]. In effect, Carnap's reconstruction of analyticity expounded Hume's fork, affirming its analytic-synthetic distinction. This would be critically important in rendering the verification principle compatible with mathematics and logic.<ref>{{cite book |title=Realistic Rationalism |author=Jerrold J. Katz |chapter-url=https://books.google.com/books?id=szCaXDdhID8C&pg=PA69 |page=69 |chapter=The epistemic challenge to antirealism |isbn=978-0262263290 |year=2000 |publisher=MIT Press}}</ref>

===Observation-theory distinction===

{{See also|Ramsey sentence}}

[[Rudolf Carnap|Carnap]] devoted much of his career to the cornerstone [[doctrine]] of ''rational reconstruction'', whereby scientific theories can be formalised into [[predicate logic]] and the components of a theory categorised into ''[[Ramsey sentence|observation terms]]'' and ''[[Ramsey sentence|theoretical terms]]''.<ref name="sep-recon">{{cite encyclopedia |first1=Hannes |last1=Leitgeb |first2=André |last2=Carus |year=2020 |title=Supplement to "Rudolf Carnap": E. The Reconstruction of Scientific Theories |encyclopedia=The Stanford Encyclopedia of Philosophy |url=https://plato.stanford.edu/entries/carnap/reconstruct-sci-theories.html |access-date=2025-02-04 }}</ref> Observation terms are specified by direct observation and thus assumed to have fixed empirical definitions, whereas theoretical terms refer to the [[unobservable]]s of a theory, including [[abstract and concrete|abstract]] conceptions such as [[formula|mathematical formulas]]. The two categories of [[primitive notion|primitive terms]] would be interconnected in meaning via a [[deductive reasoning|deductive]] interpretative framework, referred to as ''correspondence rules''.<ref name=carnap-win>{{cite journal |first=John A. |last=Winnie |title=The Implicit Definition of Theoretical Terms |journal=J. Phil. Sci. |volume=18 |year=1967 |pages=223-229 }}</ref>

Early in his research, Carnap postulated that correspondence rules could be used to define theoretical terms from observation terms, contending that scientific knowledge could be unified by [[reductionism|reducing]] theoretical laws to "protocol sentences" grounded in observable facts. He would soon abandon this model of reconstruction, suggesting instead that theoretical terms could be defined implicitly by the [[axioms]] of a theory. Furthermore, that observation terms could, in some cases, garner meaning from theoretical terms via correspondence rules.<ref name="carnap-lt">{{cite book |first=Sebastian |last=Lutz |editor1=S. Lutz |editor2=A.T. Tuboly |chapter=Two Constants in Carnap’s View on Scientific Theories |year=2021 |doi=10.4324/9780429429835 |title=Logical Empiricism and the Physical Sciences |publisher=Routledge |pages=354-378}}</ref> Here, definition is said to be 'implicit' in that the axioms serve to exclude those interpretations that falsify the theory. Thus, axioms define theoretical terms indirectly by restricting the set of possible interpretations to those that are true interpretations.<ref name=carnap-win/>

By reconstructing the [[semantics]] of scientific language, Carnap's thesis builds upon earlier research in the reconstruction of [[syntax]], referring to [[Bertrand Russell]]'s [[logical atomism]]—the view that statements in [[natural language]] can be converted to standardised subunits of meaning assembled via a [[logical syntax]].<ref>{{cite book |last=Russell |first=Bertrand |chapter=The Philosophy of Logical Atomism [1918] |date=1988 |title=The Collected Papers of Bertrand Russell, Volume 8 |pages=157–244 |doi=10.4324/9781003557036-20 |location=London |publisher=Routledge |isbn=978-1-003-55703-6 |editor=John G Slater}}</ref> Rational reconstruction is sometimes referred to as the ''[[received view]]'' or ''syntactic view of theories'' in the context of subsequent work by [[Carl Hempel]], [[Ernest Nagel]] and [[Herbert Feigl]].<ref name=sep-recon/>

===Logicism===

By [[reductionism|reducing]] mathematics to logic, [[Bertrand Russell]] sought to convert the mathematical formulas of [[physics]] to [[symbolic logic]]. [[Gottlob Frege]] began this program of [[logicism]], continuing it with Russell, but eventually lost interest. Russell then 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>{{cite book |last=Hintikka |first=Jaako |chapter=Logicism |title=Philosophy of Mathematics |editor1=Andrew D Irvine |publisher=North Holland |location=Burlington MA |year=2009 |url=https://books.google.com/books?id=mbn35b2ghgkC&pg=PA283 |pages=283–84}}</ref>

Carnap's early anti-metaphysical works employed Russell's [[type theory|theory of types]].<ref>{{cite journal |last=Schlick |first=Moritz |year=1932 |title=The elimination of metaphysics through logical analysis of language |journal=Erkenntnis |volume=2 |issue=1 |pages=1-31 |doi=10.1007/BF01886406}} Reprinted in {{cite book |title=Logical Positivism |last=Ayer |first=Alfred Jules |pages=60-81 |year=1959 |location=New York |publisher=Free Press}}</ref> Like Russell, Carnap envisioned a universal language that could reconstruct mathematics and thereby encode physics. Yet [[Kurt Gödel]]'s [[incompleteness theorem]] showed this to be impossible, except in trivial cases, and [[Alfred Tarski]]'s [[undefinability theorem]] finally undermined all hopes of reducing mathematics to logic. Thus, a universal language failed to stem from Carnap's 1934 work ''Logische Syntax der Sprache'' (''Logical Syntax of Language''). Still, some logical positivists, including [[Carl Hempel]], continued support of logicism.<ref name=Hintikka/>

==Philosophy of science==

The logical positivist movement shed much of its revolutionary zeal following the defeat of Nazism and the decline of rival philosophies that sought radical reform, notably [[Marburg school|Marburg]] [[neo-Kantianism]], [[Edmund Husserl|Husserlian]] [[Phenomenology (philosophy)|phenomenology]] and [[Martin Heidegger|Heidegger]]'s [[existentialism|existential]] [[hermeneutics]]. Hosted in the climate of American [[pragmatism]] and [[common sense]] [[empiricism]], its proponents no longer crusaded to revise traditional philosophy into a radical ''scientific philosophy'', but became respectable members of a new philosophical subdiscipline, ''[[philosophy of science]]''.<ref name=Friedman-pxiv/> Receiving support from [[Ernest Nagel]], they were especially influential in the [[social sciences]].<ref name=Novick-p546>{{cite book |last=Novick |first=Peter |title=That Noble Dream |publisher=Cambridge University Press |year=1988 |page=546}}</ref>

===Scientific explanation===

{{See also|Deductive-nomological model}}

[[Carl Hempel]] was prominent in the development of the [[deductive-nomological model|deductive-nomological]] (DN) model, then the foremost model of [[models of scientific inquiry|scientific explanation]] defended even among critics of neo-positivism such as [[Karl Popper|Popper]].<ref name=SEPWoodward>{{cite encyclopedia |first=James |last=Woodward |url=https://plato.stanford.edu/archives/win2011/entries/scientific-explanation |title=Scientific explanation |editor=Edward N. Zalta |encyclopedia=The Stanford Encyclopedia of Philosophy |edition=Winter 2011}}</ref> According to the DN model, a scientific explanation is valid only if it takes the form of a [[deductive reasoning|deductive inference]] from a set of explanatory [[premise]]s (''explanans'') to the observation or theory to be explained (''explanandum'').<ref name=Suppe>{{cite book |last=Frederick Suppe |first=Frederick |title=The Structure of Scientific Theories |publisher=University of Illinois Press |year=1977 |url=https://books.google.com/books?id=SpvZsxCA0TIC&pg=PA619 |edition=2nd |pages=619–21}}</ref> The model stipulates that the premises must refer to at least one [[scientific law|law]], which it defines as an [[enumerative induction|unrestricted generalization]] of the [[conditional sentence|conditional]] form: "If ''A'', then ''B''".<ref>{{cite book |first=Eleonora |last=Montuschi |title=Objects in Social Science |publisher=Continuum |year=2003 |url=https://books.google.com/books?id=bQ24-BV8WSAC&pg=PA62 |pages=61–62}}</ref> Laws therefore differ from mere ''regularities'' ("George always carries only $1 bills in his wallet") which do not necessarily support [[counterfactual]] claims.<ref>{{cite book| last=Bechtel |first=William |title=Philosophy of Science: An Overview for Cognitive Science |location=Hillsdale NJ |publisher=Lawrence Erlbaum Assoc. |year=1988 |pages=25-28}}</ref> Furthermore, laws must be empirically verifiable in compliance with the verification principle.<ref name=Suppe/>

The DN model ignores causal mechanisms beyond the principle of [[constant conjunction]] ("first event ''A'' and then always event ''B''") in accordance with the [[David Hume|Humean]] [[empiricism|empiricist]] postulate that, though sequences of events are observable, the underpinning [[causality|causal principles]] are not.<ref name=SEPWoodward/> Hempel stated that well-formulated natural laws (empirically confirmed regularities) are satisfactory in approximating causal explanation.<ref name=Suppe/>

Hempel later proposed a probabilistic model of scientific explanation: The inductive-statistical (IS) model. Derivation of statistical laws from other statistical laws would further be designated as the deductive-statistical (DS) model. The DN and IS models are collectively referred to as the "covering law model" or "subsumption theory", the latter referring to the movement's stated goals of "theory reduction".<ref name=Suppe/><ref>{{cite book |first=Manfred |last=Riedel |url=https://books.google.com/books?id=It3ji_AuO3sC&dq=Covering+subsumption&pg=PA3 |chapter=Causal and Historical Explanation |pages=3–4 |editor1=Manninen J |editor2=Tuomela R. |title=Essays on Explanation and Understanding: Studies in the Foundation of Humanities and Social Sciences |location=Dordrecht |publisher=D. Reidel Publishing |year=1976}}</ref>

===Unity of science===

{{See also|Unity of science}}

Logical positivists were committed to the vision of a [[unity of science|unified science]] encompassing all scientific fields (including the [[special sciences]], such as [[biology]], [[anthropology]], [[sociology]] and [[economics]], and ''the fundamental science'', or [[fundamental physics]]) which would be synthesised into a singular [[epistemology|epistemic]] entity.<ref>{{cite journal |first=Gregory |last=Frost-Arnold |url=https://philsci-archive.pitt.edu/archive/00002005/01/PSA2004Short.rtf |title=The Large Scale Structure of Logical Empiricism: Unity of Science and the Elimination of Metaphysics |journal=Philosophy of Science |volume=72 |issue=5 |year=2005 |pages=826-838 |doi=10.1086/508113}}</ref><ref name=Suppe/> Key to this concept was the doctrine of ''theory reduction'', according to which the covering law model would be used to interconnect the special sciences and, thereupon, to [[reductionism|reduce]] all laws in the special sciences to fundamental physics.<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>

The movement envisioned a universal scientific language that could express statements with common [[semantics|meaning]] intelligible to all scientific fields. [[Rudolf Carnap|Carnap]] sought to realise this goal through the systematic reduction of the linguistic terms of more specialised fields to those of more fundamental fields. Various methods of reduction were proposed, referring to the use of [[set theory]] to manipulate logically [[primitive notion|primitive concepts]] (as in Carnap's ''Logical Structure of the World'', 1928) or via [[analytic and synthetic|analytic]] and ''a priori'' deductive operations (as described in ''Testability and Meaning'', 1936, 1937). A number of publications over a period of thirty years would attempt to elucidate this concept.<ref>{{cite book |last=Hinst |first=Peter |chapter=Carnap, Rudolf: Der logische Aufbau der Welt |date=2020 |title=Kindlers Literatur Lexikon (KLL) |pages=1–2 |doi=10.1007/978-3-476-05728-0_9509-1 |location=Stuttgart |publisher=J.B. Metzler |isbn=978-3-476-05728-0}}</ref><ref>{{cite book |last=Sarkar |first=Sahotra |chapter=Rudolf Carnap Testability and Meaning |year=2021 |title=Logical Empiricism at its Peak |pages=200–265 |doi=10.4324/9781003249573-13 |location=New York |publisher=Routledge |isbn=978-1-003-24957-3}}</ref>

==Criticism==

In the post-war period, key tenets of logical positivism, including the [[verificationism|verifiability criterion]], [[analytic-synthetic distinction]] and [[Logical positivism#Observation-theory distinction|observation-theory distinction]], drew escalated criticism.<ref name="Bunge1996"/> This would become sustained from various directions by the 1950s,<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> so that, even among fractious philosophers who disagreed on the general objectives of [[epistemology]], most would concur that the logical positivist program had become untenable.<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|Karl Popper]], [[Willard Van Orman Quine|W. V. O. Quine]], [[Norwood Russell Hanson|Norwood Hanson]], [[Thomas Samuel Kuhn|Thomas Kuhn]], [[Hilary Putnam]],<ref name=sep-vienna-circle/> as well as [[J. L. Austin]], [[Peter Strawson]], [[Nelson Goodman]] and [[Richard Rorty]].<ref>{{cite journal |last=Franco |first=Paul L. |year=2018 |title= Ordinary Language Criticisms of Logical Positivism |journal=HOPOS: The Journal of the International Society for the History of Philosophy of Science |volume=8 |issue=1 |pages=157-190}}</ref> [[Carl Hempel|Hempel]] himself became a major critic from within the movement, denouncing the positivist thesis that empirical knowledge is restricted to ''basic statements'', ''observation statements'' or ''protocol statements''.<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=https://plato.stanford.edu/entries/hempel/#SciRea |access-date=31 August 2012}}</ref>

===Karl Popper===
[[Karl Popper]], a graduate of the [[University of Vienna]], was an outspoken critic of the logical positivist movement from its inception. In ''Logik der Forschung'' (1934, published in English in 1959 as ''[[The Logic of Scientific Discovery]]'') he attacked [[verificationism]] directly, contending that the [[problem of induction]] renders it impossible for [[hypothesis|scientific hypotheses]] and other [[universal generalization|universal statements]] to be verified conclusively. Any attempt to do so, he argued, would commit the fallacy of [[affirming the consequent]], given that verification cannot—in itself—exclude alternative valid explanations for a specific phenomenon or instance of observation.<ref>{{cite book|first=Samir |last=Okasha |title=The Philosophy of Science: A Very Short Introduction |location=New York |publisher=Oxford University Press |year=2002 |page=23}}</ref> He would later affirm that the content of the verifiability criterion cannot be empirically verified, thus is meaningless by its own proposition and ultimately [[self-refuting idea|self-defeating]] as a principle.<ref name=Piep>{{cite encyclopedia |url=https://www.iep.utm.edu/pop-sci/#H3 |title=Karl Popper: Philosophy of Science |last=Shea |first=Brendan |encyclopedia=Internet Encyclopedia of Philosophy |access-date=May 12, 2019}}</ref>

In the same book, Popper proposed ''[[falsifiability]]'', which he presented, not as a criterion of ''cognitive meaning'' like verificationism (as commonly misunderstood),<ref name="Hacohen">{{cite book |title=Karl Popper: The Formative Years, 1902–1945: Politics and Philosophy in Interwar Vienna |last=Hacohen |first=Malachi Haim |year=2000 |publisher=Cambridge University Press |location=Cambridge |pages=212-13}}</ref> but as a criterion to distinguish scientific from non-scientific statements, thereby to [[demarcation problem|demarcate the boundaries of science]]. Popper observed that, though universal statements cannot be verified, they can be falsified, and that the most productive scientific theories were apparently those that carried the greatest 'predictive risks' of being falsified by observation.<ref name=PopperAE>{{cite book |title=Conjectures and Refutations: The Growth of Scientific Knowledge |last=Popper |first=Karl |year=1962 |publisher=Routledge |edition=2nd |pages=34-37}}</ref> He would conclude that the [[scientific method]] should be a [[hypothetico-deductive model]], wherein scientific hypotheses must be falsifiable (per his criterion), held as provisionally true until proven false by observation, and are ''corroborated'' by supporting evidence rather than verified or confirmed.<ref name=Popper>{{cite book |last=Popper |first=Karl |title=The Logic of Scientific Discovery |doi=10.4324/9780203994627 |publisher=Routledge |location=London |year=2005 |edition=2nd}}</ref>

In rejecting neo-positivist views of cognitive meaningfulness, Popper considered [[metaphysics]] to be rich in meaning and important in the origination of scientific theories and [[value system]]s to be integral to science's quest for truth. At the same time, he disparaged [[pseudoscience]], referring to the [[confirmation bias]]es that embolden support for unfalsifiable conjectures (notably those in [[psychology]] and [[psychoanalysis]]) and ''[[ad hoc]]'' arguments used to entrench predictive theories that have been proven conclusively false.<ref name=PopperAE/>

===Willard V. O. Quine===

In his influential 1951 paper ''[[Two Dogmas of Empiricism]]'', American philosopher and [[logicism|logicist]] [[Willard Van Orman Quine]] challenged the [[Logical positivism#Analytic-synthetic distinction|analytic-synthetic distinction]].  Specifically, Quine examined the concept of [[Two Dogmas of Empiricism#Analyticity and circularity|analyticity]], determining that all attempts to explain the idea reduce ultimately to [[circular reasoning]]. He would conclude that, if analyticity is untenable, so too is the neo-positivist proposition to redefine its boundaries.<ref>{{cite journal |first=Willard V. O. |last=Quine |title=Two Dogmas of Empiricism |journal=Philosophical Review |year=1951 |volume=60 |pages=20–43}} collected in {{cite book |first=Willard V. O. |last=Quine |title=From a Logical Point of View |location=Cambridge MA |publisher=Harvard University Press |year=1953}}</ref> Yet [[Rudolf Carnap|Carnap]]'s reconstruction of analyticity was necessary for logic and mathematics to be deemed meaningful under verificationism. Quine's arguments encompassed numerous criticisms on this topic he had articulated to Carnap since 1933.<ref name=IEPQ>{{cite encyclopedia |url=https://iep.utm.edu/quine-an/#H2 |title=Willard Van Orman Quine: The Analytic/Synthetic Distinction |last=Rocknak |first=Stefanie |encyclopedia=Internet Encyclopedia of Philosophy |access-date= July 14, 2024}}</ref> His work effectively pronounced the verifiability criterion untenable, threatening to uproot the broader logical positivist project.<ref>{{cite book |last=Shieh |first=Sanford |chapter=Logical Positivism and Quine |title=A Companion to the Philosophy of Language |year=2012 |publisher=Routledge |pages=869-872 |editor1=D. Graff Fara |editor2=G. Russell}}</ref>

===Norwood Hanson===

In 1958, [[Norwood Russell Hanson|Norwood Hanson]]'s ''Patterns of Discovery'' characterised the concept of [[theory-laden|theory-ladenness]]. Hanson and [[Thomas Kuhn]] held that even direct observations are never truly neutral in that they are ''laden with theory'', i.e. influenced by a system of theoretical [[presuppositions]] that function as an interpretative framework for the [[sense data|senses]].<ref>{{cite book |title=Beyond Positivism: Economic Methodology in the 20th Century |last=Caldwell|first=Bruce|pages=47-48 |year=1994 |publisher=Routledge |location=London}}</ref> Accordingly, individuals subscribed to different theories might report radically different observations even as they investigate the same phenomena. Hanson's thesis attacked the [[Logical positivism#Observation-theory distinction|observation-theory distinction]], which draws a dividing line between observational and non-observational (theoretical) language. More broadly, its findings challenged the central-most tenets of [[empiricism]] in questioning the infallibility and objectivity of empirical observation.<ref>{{cite encyclopedia |first=Nora Mills |last=Boyd |editor=Edward N. Zalta |year=2009 |edition=2021 |title=Theory and Observation in Science |encyclopedia=The Stanford Encyclopedia of Philosophy |url=https://plato.stanford.edu/entries/science-theory-observation/ |access-date=29 January 2025}}</ref>

===Thomas Kuhn===

[[Thomas Samuel Kuhn|Thomas Kuhn]]'s landmark book of 1962, ''[[The Structure of Scientific Revolutions]]''—which discussed [[paradigm shift]]s in [[fundamental interactions|fundamental physics]]—critically undermined confidence in scientific [[foundationalism]].<ref>{{cite book |title=Philosophy of Science: A Very Short Introduction |last=Okasha|first=Samir|year=2002 |chapter=Scientific Change and Scientific Revolutions |publisher=Oxford University Press |location=Oxford}}</ref> Kuhn proposed in its place a [[coherentism|coherentist]] model of science, whereby scientific progress revolves around cores of established, coherent ideas which periodically undergo abrupt revolutionary changes.<ref>{{cite journal |last=Daston |first=Lorraine |year=2020 |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>

Though foundationalism was often considered a constituent doctrine of logical positivism (and Kuhn's thesis an [[epistemological]] criticism of the movement) such views were simplistic:<ref>{{harvnb|Uebel|2008}} 3.3</ref> In the 1930s, [[Otto Neurath|Neurath]] had argued for the adoption of [[coherentism]], famously comparing the progress of science to [[Neurath's boat|reconstruction of a boat 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 University Press |year=2008 |isbn=978-0521041119 |chapter=On Neurath's Boat |pages=89–94}}</ref> [[Rudolf Carnap|Carnap]] had entertained foundationalism from 1929 to 1930, but he, [[Hans Hahn (mathematician)|Hans Hahn]] and others would later join Neurath in converting to a coherentist philosophy. The [[Logical positivism#Vienna and Berlin Circles|conservative wing]] of the [[Vienna Circle]] under [[Moritz Schlick]] subscribed to a form of foundationalism, but its principles were defined unconventionally or ambiguously.<ref>{{harvnb|Uebel|2008}} 3.3 Uebel writes, "Even Schlick conceded, however, that all scientific statements were fallible ones, so his position on foundationalism was by no means the traditional one. The point of his “foundations” remained less than wholly clear and different interpretation of it have been put forward."</ref>

In some sense, Kuhn's book unified science, but through historical and social assessment rather than by [[Logical positivism#Unity of science|networking the scientific specialties]] using epistemological or [[linguistics|linguistic]] models.<ref name=Novick-p526>{{harvnb|Novick|1988}} pp. 526–27</ref> His ideas were adopted quickly by scholars in non-scientific disciplines, such as the social sciences in which neo-positivists were dominant,<ref name=Novick-p546/> ushering academia into [[postpositivism]] or postempiricism.<ref name=Novick-p526/>

===Hilary Putnam===

In his critique of the [[received view of theories|received view]] in 1962, [[Hilary Putnam]] attacked the [[Logical positivism#Observation-theory distinction|observation-theory distinction]].<ref>{{cite book |title=Logic, Methodology, and Philosophy of Science |last=Putnam |first=Hilary |pages=240–251 |chapter=What Theories are Not |year=1962 |publisher=Stanford University Press |location=Stanford |editor1= E. Nagel |editor2=P. Suppes |editor3=A. Tarski }}</ref> Putnam proposed that the division between "observation terms" and "theoretical terms" was untenable, determining that both categories have the potential to be [[theory-laden]]. Accordingly, he remarked that observational reports frequently refer to theoretical terms in practice.<ref>{{cite book |first=Hilary |last=Putnam |chapter=Problems with the observational/theoretical distinction |title=Scientific Inquiry |editor=Robert Klee |location=New York |publisher=Oxford University Press |year=1999 |pages=25–29}}</ref> He illustrated cases in which observation terms can be applied to entities that [[Rudolf Carnap|Carnap]] would classify as [[unobservable]]s. For example, in [[Isaac Newton|Newton]]'s [[corpuscular theory of light]], observation concepts can be applied to the consideration of both [[Orders of magnitude (volume)#Sub-microscopic|sub-microscopic]] and macroscopic objects.<ref>{{cite encyclopedia |last=Andreas |first=Holger |editor=Edward N. Zalta |year=2013 |edition=August 2021 |title=Theoretical Terms in Science |encyclopedia=The Stanford Encyclopedia of Philosophy |url=https://plato.stanford.edu/entries/theoretical-terms-science/ |access-date=30 January 2025}}</ref>

Putnam advocated [[scientific realism]], whereby scientific theory describes a [[reality|real world]] existing independently of the senses. He rejected positivism, which he dismissed as a form of [[idealism|metaphysical idealism]], in that it precluded any possibility to acquire knowledge of the unobservable aspects of nature. He also spurned [[instrumentalism]], according to which a scientific theory is judged, not by whether it corresponds to reality, but by the extent to which it allows empirical predictions or resolves conceptual problems.<ref name="Friedman-pxii"/>

==Decline and legacy==

In 1967, [[John Passmore]] wrote, "Logical positivism is dead, or as dead as a philosophical movement ever becomes".<ref name=hanfling>{{cite book |title=Philosophy of Science, Logic and Mathematics in the Twentieth Century |chapter=Logical positivism |last=Hanfling |first=Oswald| editor=Stuart G Shanker |year=1996 |publisher=Routledge |pages=193-94}}</ref> His opinions concurred with widespread sentiment in academic circles that the movement had run its course by the late 1960s.<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=508 |isbn=978-0-19-866132-0 |url=https://archive.org/details/oxfordcompaniont00hond/page/508 }}</ref> Logical positivism's fall heralded [[postpositivism]], distinguished by [[Karl Popper|Popper]]'s [[critical rationalism]]—which characterised human knowledge as continuously evolving via conjectures and refutations—and [[Thomas S. Kuhn|Kuhn]]'s historical and social perspectives on the saltatory course of scientific progress.<ref>{{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>

In a 1976 interview, [[A. J. Ayer]], who had introduced logical positivism to the [[English-speaking world]] in the 1930s,<ref>{{cite book |title=Key ideas in linguistics and the philosophy of language |chapter=Logical positivism |last=Chapman |first=Siobhan| editor1=Siobhan Chapman |editor2=Christopher Routledge |year=2009 |publisher=Edinburgh University Press |location=Edinburgh}}</ref> was asked what he saw as its main defects and answered that, "nearly all of it was false". Yet, he maintained that it was "true in spirit", referring to the principles of [[empiricism]] and [[reductionism]] whereby [[physicalism|mental phenomena resolve to the material or physical]] and philosophical questions largely resolve to ones of language and meaning.<ref name=hanfling/><ref>{{cite web |url=https://www.youtube.com/watch?v=4cnRJGs08hE |title=Ayer on Logical Positivism: Section 4 |website=[[YouTube]] |at=6:30}}</ref> Despite its problems, logical positivism helped to anchor [[analytic philosophy]] in the English-speaking world and its influence extended beyond philosophy in shaping the course of [[psychology]] and the [[social sciences]]. In the post-war period, [[Carl Hempel]]'s contributions were vitally important in establishing the subdiscipline of the [[philosophy of science]].<ref name="Friedman-pxii"/>

Logical positivism's fall reopened the debate over the [[metaphysics|metaphysical]] merit of scientific theory, whether it can offer knowledge of the world beyond human experience ([[scientific realism]]) or whether it is simply an instrument to predict human experience ([[instrumentalism]]).<ref>{{cite book |first=Hilary |last=Putnam |chapter=What is realism? |editor=Jarrett Leplin |title=Scientific Realism |publisher=University of California Press |year=1984 |page=140 |url=https://books.google.com/books?id=zhBeVFm8WuAC&dq=Realism+realists+positivism+opera-tionalism&pg=PA140}}</ref><ref>{{cite journal |first=Ruth |last=Lane |doi=10.1177/0951692896008003003 |title=Positivism, scientific realism and political science: Recent developments in the philosophy of science |journal=Journal of Theoretical Politics |year=1996 |volume=8 |issue=3 |pages=361–82}}</ref> Philosophers increasingly critiqued the movement's doctrine and history, often misrepresenting it without thorough examination,<ref>{{harvnb|Friedman|1999}} p. 1</ref> sometimes reducing it to oversimplifications and stereotypes, such as its association with [[foundationalism]].<ref>{{harvnb|Friedman|1999}} p. 2</ref>

==See also==
{{cols}}
* {{Annotated link |Definitions of philosophy}}
* {{Annotated link |Anti-realism}}
* {{Annotated link |Sociological positivism}}
* {{Annotated link |Academic skepticism}}
* {{Annotated link |The Structure of Science}}
* {{Annotated link |Raven paradox}}
* {{Annotated link |Unobservable}}
{{colend}}

===People===
* {{Annotated link |Ernst Mach}}
* {{Annotated link |Gottlob Frege}}
* {{Annotated link |Friedrich Waismann}}
* {{Annotated link |Gustav Bergmann}}
* {{Annotated link |Herbert Feigl}}
* {{Annotated link |Kurt Grelling}}
* {{Annotated link |R. B. Braithwaite}}

==References==
{{Reflist}}

==Further reading==
{{refbegin}}
*{{cite book |last1=Achinstein |first1=Peter |last2=Barker |first2=Stephen F. |title=The Legacy of Logical Positivism: Studies in the Philosophy of Science |location=Baltimore |publisher=Johns Hopkins Press |year=1969}}
*{{cite book |last=Bergmann |first=Gustav |title=The Metaphysics of Logical Positivism |location=New York |publisher=Longmans Green |year=1954}}
*{{cite book |last=Cirera |first=Ramon |title=Carnap and the Vienna Circle: Empiricism and Logical Syntax |location=Atlanta, GA |publisher=Rodopi |year=1994}}
*{{cite SEP |url-id=logical-empiricism/ |title=Logical Empiricism |last=Creath |first=Richard}}
*{{cite book |last=Gadol |first=Eugene T. |title=Rationality and Science: A Memorial Volume for Moritz Schlick in Celebration of the Centennial of his Birth |location=Wien |publisher=Springer |year=1982}}
*{{cite book |last1=Giere |first1=Ronald N. |last2=Richardson |first2=Alan W. |title=Origins of Logical Empiricism |location=Minneapolis |publisher=University of Minnesota Press |year=1997}}
*{{cite SEP |url-id=probability-interpret/ |title=Interpretations of Probability |last=Hájek |first=Alan}}
*{{cite journal |first=Jim |last=Holt |title=Positive Thinking |journal=The New York Review of Books |volume=64 |issue=20 |year=2017 |pages=74–76}}
*{{cite book |last=Jangam |first=R. T. |title=Logical Positivism and Politics |location=Delhi |publisher=Sterling Publishers |year=1970}}
*{{cite book |last1=Janik |first1=Allan |last2=Toulmin |first2=Stephen |title=Wittgenstein's Vienna |location=London |publisher=Weidenfeld and Nicolson |year=1973}}
*{{cite book |last=Kraft |first=Victor |title=The Vienna Circle: The Origin of Neo-positivism, a Chapter in the History of Recent Philosophy |location=New York |publisher=Greenwood Press |year=1953}}
*{{cite book |last=McGuinness |first=Brian |title=Wittgenstein and the Vienna Circle: Conversations Recorded by Friedrich Waismann |editor1=Joachim Schulte |editor2=Brian McGuinness |location=New York |publisher=Barnes & Noble Books |year=1979}}
*{{cite book |editor=Milkov, Nikolay |title=Die Berliner Gruppe. Texte zum Logischen Empirismus von Walter Dubislav, Kurt Grelling, Carl G. Hempel, Alexander Herzberg, Kurt Lewin, Paul Oppenheim und Hans Reichenbach |location=Hamburg |publisher=Meiner |year=2015}}
*{{cite book |last=Mises von |first=Richard |title=Positivism: A Study in Human Understanding |location=Cambridge |publisher=Harvard University Press |year=1951}}
*{{cite book |last=Murzi |first=Mauro |chapter=Logical Positivism |title=The New Encyclopedia of Unbelief |editor=Tom Flynn |publisher=Prometheus Books |year=2007}}
*{{cite book |last=Parrini |first=Paolo |title=Empirismo logico e convenzionalismo: saggio di storia della filosofia della scienza |location=Milano |publisher=F. Angeli |year=1983}}
*{{cite book |editor1=Parrini, Paolo |editor2=Salmon, Wesley C. |editor3=Salmon, Merrilee H. |title=Logical Empiricism – Historical and Contemporary Perspectives |location=Pittsburgh |publisher=University of Pittsburgh Press |year=2003}}
*{{cite book |last=Passmore |first=John |chapter=Logical Positivism |title=The Encyclopedia of Philosophy |editor=Paul Edwards |location=New York |publisher=Macmillan |year=1967 |edition=1st}}
*{{cite book |last=Reisch |first=George |title=How the Cold War Transformed Philosophy of Science: To the Icy Slopes of Logic |location=New York |publisher=Cambridge University Press |year=2005}}
*{{cite book |last=Rescher |first=Nicholas |title=The Heritage of Logical Positivism |location=Lanham, MD |publisher=University Press of America |year=1985}}
*{{cite book |editor1=Alan Richardson |editor2=Thomas Uebel |title=The Cambridge Companion to Logical Positivism |location=New York |publisher=Cambridge University Press |year=2007}}
*{{cite SEP |url-id=genrel-early/ |title=Early Philosophical Interpretations of General Relativity |last=Ryckman |first=Thomas A.}}
*{{cite book |editor1=Salmon, Wesley |editor2=Wolters, Gereon |title=Logic, Language, and the Structure of Scientific Theories: Proceedings of the Carnap-Reichenbach Centennial, University of Konstanz, 21–24 May 1991 |location=Pittsburgh |publisher=University of Pittsburgh Press |year=1994}}
*{{cite book |editor=Sarkar, Sahotra |url=https://books.google.com/books?id=eS8jeSgy8eIC&q=positivism |title=The Emergence of Logical Empiricism: From 1900 to the Vienna Circle |location=New York |publisher=Garland Publishing |year=1996}}
*{{cite book |editor=Sarkar, Sahotra |url=https://books.google.com/books?id=H-OdzRfpehEC&q=positivism |title=Logical Empiricism and the Special Sciences: Reichenbach, Feigl, and Nagel |location=New York |publisher=Garland Publishing |year=1996}}
*{{cite book |editor=Sarkar, Sahotra |url=https://books.google.com/books?id=NiQBRoKrVW0C&q=positivism |title=Decline and Obsolescence of Logical Empiricism: Carnap vs. Quine and the Critics |location=New York |publisher=Garland Publishing |year=1996}}
*{{cite book |editor=Sarkar, Sahotra |url=https://books.google.com/books?id=FJ68n_9XXAwC&q=positivism |title=The Legacy of the Vienna Circle: Modern Reappraisals |location=New York |publisher=Garland Publishing |year=1996}}
*{{cite book |editor=Spohn, Wolfgang |url=https://books.google.com/books?id=ED3sCAAAQBAJ&q=positivism |title=Erkenntnis Orientated: A Centennial Volume for Rudolf Carnap and Hans Reichenbach |location=Boston |publisher=Kluwer Academic Publishers |year=1991}}
*{{cite book |last=Stadler |first=Friedrich |url=https://books.google.com/books?id=2rAlCQAAQBAJ&q=positivism |title=The Vienna Circle. Studies in the Origins, Development, and Influence of Logical Empiricism |location=Dordrecht|publisher=Springer |year=2015 |edition=2nd}}
*{{cite book |editor=Stadler, Friedrich |title=The Vienna Circle and Logical Empiricism. Re-evaluation and Future Perspectives |location=Dordrecht |publisher=Kluwer |year=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)]

'''Articles on logical positivism'''
* [http://www.philosophypages.com/hy/6q.htm Kemerling, Garth. 'Logical Positivism', ''Philosophy Pages'']
* [http://murzim.net/LP/LP00.html Murzi, Mauro. 'The Philosophy of Logical Positivism.']

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