A.J. Ayer (1910–1989) was only 24 when he wrote the book thatmade his philosophical name,Language, Truth, and Logic(hereafterLTL), published in 1936. In it he put forward whatwere understood to be the major theses of logical positivism, and soestablished himself as the leading English representative of themovement, Viennese in origin. In endorsing these views Ayer sawhimself as continuing in the line of British empiricism established byJohn Locke and David Hume, an empiricism whose most recentrepresentative was Bertrand Russell. Throughout his subsequent careerhe remained true to this tradition’s rejection of thepossibility of synthetica priori knowledge, and so he sawthe method of philosophy to be the analysis of the meaning of keyterms, such as ‘causality’, ‘truth’,‘knowledge’, ‘freedom’, and so on. The majorportion of his work was devoted to exploring different facets of ourclaims to knowledge, particularly perceptual knowledge and knowledgethat depended on inductive inference for its credence. Along the wayhe defended a ‘justified true belief’ account ofknowledge, a Humean account of causation, and compatibilism withrespect to freedom. InLTL he put forward an emotivist theoryof ethics, one that he never abandoned.

Ayer always wrote with stylish crispness and clarity; he could laybare the bones of a philosophical difficulty in a few paragraphs ofstrikingly simple prose. On many a philosophical problem Ayer cannotbe bettered for providing a lucid, informative, and revealingdescription of its contours. Above all, on reading an essay of his,whether it be on basic propositions, sense data, induction, orfreedom, one comes away recognizing that the aim of the author hasbeen to reach the truth, no matter what that turned out to be.Unfortunately, he sometimes rushed to reach it, which, together withthe directness of his style, gave him a reputation for mere clevernessthat he never lived down. Nevertheless, amongst British philosophersof the 20^th Century he has been ranked as second only toRussell (Foster 1985); P.F. Strawson, at his memorial service, statedthat his contribution to the theory of knowledge and generalmetaphysics was “in no way inferior to Russell’s”(see Rogers 1999, 358).

• 1. Biographical Sketch
• 2. The Function and Nature of Philosophy
  • 2.1. Philosophical Analysis
  • 2.2. Philosophy and Science
  • 2.3. Philosophy and Metaphysics
• 3. Meaning and Truth
  • 3.1 Meaning
  • 3.2 Truth
• 4. Perception
• 5. Induction and Probability
• 6. Knowledge
• 7. Necessity, Causality, and Freedom
• 8. Ethics
• Bibliography
  • Primary Literature: Works by Ayer
  • Primary Literature: Works on Ayer
• Academic Tools
• Other Internet Resources
• Related Entries

1. Biographical Sketch

Alfred Jules Ayer was born in London on October 29, 1910. His mother,Reine, was descended from Dutch Jews, whilst his father, Jules LouisCypress Ayer, came from a Swiss Calvinist background. As recounted inRogers 1999, Ayer was a precocious but mischievous child, and so wassent to boarding school (outside Eastbourne) at the age of seven, fromwhich he won a scholarship to Eton in 1923. There he impressed hispeers with his intelligence and competitiveness, the latter traitmanifesting itself in the way he played games. Ayer nevertheless feltan ‘outsider’, and it is clear that his fellow-studentsdid not warm to him, perhaps due to the excessive zeal with which heattempted to convert them to atheism. Feeling ‘anoutsider’ was something that remained with him all his life. Atthe age of sixteen he specialized in classics and at the same timestarted reading some philosophy. Bertrand Russell’sSceptical Essays made an impression, particularlyRussell’s argument for the claim that it is undesirable tobelieve a proposition when there is no ground for believing its truth.Ayer said that this remained a motto for him throughout hisphilosophical career (see Rogers 1999, 45). At the same time a readingof G.E. Moore’sPrincipia Ethica also had a lastingeffect, particularly Moore’s articulation of the NaturalisticFallacy.

The Easter before leaving Eton, Ayer spent some time in Paris, wherehe met Renee Lees, whom he subsequently married (in 1933). Thefollowing year (1929) he won a classics scholarship to Christ Church,Oxford, where he studied both Greek and philosophy, one of his tutorsbeing Gilbert Ryle (for the Oxford atmosphere, see Berlin 1973; Ryle1970, 1976, 1999; Mehta 1965; for a comprehensive narrative seeKrishnan 2023). It was Ryle who suggested that Ayer read LudwigWittgenstein’sTractatus Logico-Philosophicus; as thebook immediately impressed him, Ayer gave a paper on the Tractatus inearly March 1932 to the Jowett Society in Oxford (a group intended forundergraduates, see Rowe 2023, p. 91). After graduation, Ayer wantedto study with Wittgenstein in Cambridge, but Ryle had a differentsuggestion. As Wittgenstein was less relevant in Oxford, and sinceRyle had met Moritz Schlick, then leader of theVienna Circle, at the InternationalCongress for Philosophy in Oxford in 1930, he encouraged Ayer to go toVienna and bring home the Circle’s latest views and results toperform a “public service” (Ayer 1977, 121). Thus Ayerwent to Vienna, contacted Schlick to enter his philosophy of naturecourse at the university and attended the private meetings of theCircle in the library of the Mathematical Institute. Between Januaryand March 1933 (when Ayer returned to Oxford), it was mainly Schlick,Friedrich Waismann, Hans Hahn, Karl Menger, Kurt Gödel,occasionally Otto Neurath and presumably Felix Kaufmann who werepresent at the discussions (Rudolf Carnap was already in Prague thattime), along with W. V. O. Quine. His philosophical experience inVienna was somewhat limited by his uncertain knowledge of German (ashe wrote to Ryle, “[o]n the whole I have got very little out ofthem all” [Ayer to Ryle, February 19, 1933, quoted inHarré and Shosky 1999, 31]), but he knew enough to pick up thebasic tenets of logical positivism (on the similarities anddifferences between Ayer and logical positivism, see Koterski 2023,Pincock 2022, Tuboly 2021b, pp. 28–33, and Vrahimis 2021).

After leaving Vienna, Ayer lectured for a short time at Christ Church,where in 1935 he was elected to a five-year research fellowship. Inthe same year he finishedLTL, which caused a great deal ofcontroversy and debate, partly for its sweeping dismissal ofmetaphysics, but especially for the metaethical emotivism Ayerchampioned in one of its most notorious chapters. During the next fewyears, Ayer worked at defending and refining some of the positionsadopted inLTL, not least at meetings in Oxford with IsaiahBerlin, Stuart Hampshire, and J.L. Austin. The confrontations withAustin were to prove long-lasting. The product of this refiningprocess was the bookFoundations of Empirical Knowledge.During this time he also enjoyed life to the full; he was a gooddancer, once confessing that he would have preferred to be atap-dancer rather than a professional philosopher, but had given up onthe idea when he recognized that he would never be as good as FredAstaire. His marriage to Renee started to disintegrate; Ayer hadnumerous affairs, and Renee formed an enduring relationship withStuart Hampshire.

In the immediate pre-war years, Ayer had become passionate aboutpolitics. He supported the Republican side in Spain, flirted withjoining the Communist Party, but instead became an active member ofthe Labour Party. When war was declared he joined the Welsh Guards(and was helped to do so by Gilbert Ryle). He worked for a while inCambridge interrogating prisoners, then was sent to America to join asecret service mission, one which seemed to involve gatheringinformation about Fascist sympathizers in America. Whilst in New Yorkhe reviewed films for theNation, fathered a daughter (SheilaGraham was the mother), and made a record with Lauren Bacall. On beingrepatriated to England, Ayer found himself given the job of helpingwith the organization of the French resistance movements in London.Shortly after the war he was posted to Paris, where he took theopportunity to study French existentialism, writing articles on Sartreand Camus inHorizon.

On his release from Army service Ayer accepted the offer of a tutorialfellowship at Wadham College, Oxford, but was there only a short whilebefore becoming the Grote Professor of Philosophy at UniversityCollege, London, at the age of 36. He quickly appointed Hampshire to alectureship (making up for having cited Hampshire as co-respondent inhis divorce from Renee), then Richard Wollheim. The department grewand became a thriving philosophical center. Ayer also ventured intothe world of radio, being involved in many BBC Third Programmebroadcasts, including panel discussions with the scientists Zuckerman,Huxley and Medawar, and a famous debate with the Jesuit priestFrederick Copleston on the existence of God. Later he became a regularperformer on BBC television’s “The Brains Trust”. In1948 he lectured at Bard College in New York, but it proved to be anunhappy experience. Back in London C.E.M. Joad had published anarticle in theNew Statesman arguing thatLTL wasresponsible for creating an environment in which Fascism flourished,andTime magazine published an unflattering short articleclaiming that Ayer taught his students that “That man is good tosupport his mother” was a meaningless statement (Rogers 1999, p.232). On his return to Europe he started a hectic schedule of lecturetours, visiting France, Belgium, Italy, Sweden, Denmark, Peru, Chile,Uruguay, and Brazil, all in the early 1950s.

In 1958 Ayer took the opportunity to return to Oxford as WykehamProfessor of Logic. He later said that this decision was made in orderto combat the growing influence of Austin, who had made a point ofattacking Ayer’s views on perception. Austin was, however, soonto die, making Ayer’s ‘sacrifice’ of his life inLondon somewhat pointless. Not that it was completely sacrificed; hebi-located, spending long weekends in London with his second wife, DeeWells, and at most three nights in New College during the week. Hecontinued to travel widely: China, Russia, India, and Pakistan wereadded to the itinerary. He also continued his political activity,continuing to support the Labour Party, campaigning against Britishinvolvement in Vietnam, and being at one time Vice-President of theSociety for the Reform of the Abortion Law, Chairman of the CampaignAgainst Racial Discrimination in Sport, and President of theHomosexual Law Reform Society. His support for the decriminalizationof homosexual behavior, he once quipped, could not be thought byanyone acquainted with him to involve a vested interest. Ayer’ssupport for the Labour Party came to an end with the formation of theSocial Democratic Party in 1981. His support for the SDP was a protestat the leftward trend of the Labour Party, and particularly itsanti-Europeanism.

The arrangement of spending long weekends in London and some of theworking week in Oxford added to Ayer’s turbulent domestic life.In 1963 he and Dee Wells had a son, Nicholas, of whom Ayer said,“My love for this child has been a dominating factor in theremainder of my life” (Rogers 1999, 278.) He formed arelationship with Vanessa Lawson, whom he would see whilst in Oxford.During this time, Ayer continued to be philosophically productive,doing some of his most original work.The Origins ofPragmatism was published in 1968, following thisRussell andMoore: the Analytical Heritage (the product of the William Jameslectures he delivered at Harvard in 1970), andProbability andEvidence (the Dewey lectures delivered at Columbia University in1970). Shortly thereafter cameRussell, a small paperback,andThe Central Questions of Philosophy (1973, originallygiven as the Gifford Lectures at the University of St. Andrews), inwhich he elaborated on the sophisticated realism first put forward inThe Origins of Pragmatism. He visited Canada on a couple ofoccasions, giving the Gilbert Ryle lectures at Trent University (1979)resulting in his book on Hume, and the Whidden lectures at McMaster(1983) giving rise toFreedom and Morality.

Shortly after being divorced from Dee Wells, Ayer married VanessaLawson in 1982. Shortly before that Renee, his first wife, had died(1980), followed by Valerie, their daughter, who died suddenly ofHodgkin’s disease in 1981. Tragically Vanessa was to die ofliver cancer in 1985, leaving Ayer grief-stricken. He himself had aclose encounter with death, being ‘technically’ dead for afew minutes after choking on a piece of smoked salmon. On reviving hereported his experience whilst ‘dead’ in such a way as toprovide fodder for those who thought the famous atheist had recantedand found God. He moved quickly to dispel these rumours. By this timehe had become something of a philosophical Grand Old Man, with volumespublished in his honour, and a full-length critical study by JohnFoster in the prestigious Routledge “arguments of thephilosophers” series. He spent most of the remaining couple ofyears responding to articles that were to appear in the Ayer volume inthe Library of Living Philosophers series, edited by L.E. Hahn. Heremarried Dee Wells, but not long afterwards Ayer was admitted tohospital with a collapsed lung in the early summer of 1989 and died onthe 27^th, June.

Ayer wrote two autobiographies,Part of My Life, andMoreof My Life. His circle of friends included many famous andinfluential people; the following (in no particular order) is only abrief list. Cyril Connolly, Graham Greene, George Orwell, ee cummingsand his wife Marianne, Meyer Schapiro, Arthur Koestler, BertrandRussell, Stephen Spender, W.H. Auden, Philip Toynbee, Isaiah Berlin,Hugh Gaitskell, Roy Jenkins, Michael Foot, Richard Crossman, JonathanMiller, Angus Wilson, Alan Bennett, Alice Thomas Ellis, Joan Fontaine,Iris Murdoch, V.S. Pritchett, and Christopher Hitchens. He believed,maybe truly, that the character of George Moore in TomStoppard’s playJumpers was modeled on him. Ayer was avain man whose vanity was part of his considerable charm. He made adistinction between vanity and egotism; an egotist, he said, thoughthe should have more medals, whilst a vain person just enjoyed showingoff the medals he had. Among the many ‘medals’ given toAyer were his knighthood, Fellow of the British Academy, honorarymember of the American Academy of Arts and Sciences, Member of theBulgarian Order of Cyril and Methodius, 1^st class, andChevalier of the Légion d’honneur.

2. The Function and Nature of Philosophy

2.1. Philosophical Analysis

InLTL, Ayer defines the task of philosophy ascritical-linguistic analysis of scientific and common-sensestatements. He dismissed such traditional conceptions that view thepropositions of philosophy as first principles, or conceivedphilosophy’s task as vindicating scientific statements(LTL, pp. 46–50). What remained for him is that thepropositions of philosophy “are not factual, but linguistic incharacter” (LTL, p. 57). That does not mean, however,that philosophy is about the everyday usage of words (as in certainforms of the emerging ordinary language philosophy, see Chapman 2021and Parker-Ryan 2021 for comparisons), because the propositions ofphilosophy would be empirical in character then (like linguistics,sociology, or anthropology), but Ayer wanted to differentiatephilosophy from the sciences. Rather, philosophy is concerned withclasses or types of expressions (like definitions) and thus it isclarificatory on a more abstract level, dealing, for example, with theformal consequnces of defitions and their inter-linguistic relations(LTL, p. 26).

To give an example, Ayer uses Russell’s theory of descriptions (see the SEP entry on that). It illustrates how one can define a certain symbol by translating thesentence which contains it into an equivalent sentence that containsneither the term in questions, nor any of its synonyms (LTL,p. 60). Following Russell, Ayer shows that the relevant term is infact a description and not a referential phrase as it was initiallythought, thus philosophy reveals ahidden logical structure.Philosophy starts with certain known and common expressions, revealstheir structure and logical features, and hence therapeuticallydismisses the relevant and associated philosophical problems through alogico-linguistic analysis. For the early Ayer, philosophy was seenexplicitly as “a department of logic” (LTL, p. 57).

Nonetheless,LTL does not contain much about logicperse. When Ayer was in Vienna, he wrote to Ryle that “theproblems of pure logistic do not interest me very much”(Harré and Shosky 1999, p. 32). Concrete logical formalism doesnot play much role in solving philosophical problems inLTL,just as metalogical axiomatizations, ideally constructed first orderlanguages, or syntactical derivations are largely absent fromAyer’s work. Although he endedLTL by stating thatphilosophy has to become the logic of science (LTL, p. 153),the book does not contain anything like that in the style and fashionof Carnap (not even references to hisLogische Syntax derSprache) but pursues a general linguistic analysis that looselydraws from Carnap and Schlick-Wittgenstein alike.

Later, in 1973, Ayer defined philosophy, very much in line withLTL, as a field that is concerned with many subjects (likeethics, knowledge, logic), but in all cases, it deals with criteria,standards, assessments, and methods (1973, p. 2) and not with concreteempirical data or observations. In that sense, philosophy functionsrather as some sort of meta-discipline that has a general view of itsmany subjects, and investigates those abstract categories, concepts,and frameworks that are used in first-order inquiries and“dominate all our thinking” (1962, p. 19).

2.2. Philosophy and Science

Regarding science and its relation to philosophy, Ayer (1977, p. 163)admitted later that he “had little skill in mathematics and noscientific training”. AlthoughLTL does not containanything about the traditional debates surrounding the foundations ofmathematics (just a general discussion about the analytic character ofmathematical and logical propositions), Ayer’s lack ofscientific knowledge was even more substantial and manifest given theline of argumentation ofLTL that pointed in the equation ofphilosophy with the logic ofscience.

For Ayer, science had speculative and logical parts, where the formerwas pursued by the scientists who formulated hypotheses and guesses,and the latter (the investigation of thelogical relationsbetween these hypotheses, and the logical definition of the symbolsinvolved) was the object of philosophizing. The “essential” assumptionhere was that the inquirer or analyzer had to “understand science” toproperly accomplish the logical task, and thus for the philosopherswho do the logic of science and analyze scientific symbols “itis necessary to become scientist[s]” if their aim is tocontribute to the growth of human knowledge (LTL, p. 153).Most logical empiricists, having substantial training or even degreesin natural science, did not have any problem with that.Electromagnetic theory, relativity theory, quantum mechanics andoptics were in the focus of their investigations, along with highlyadvanced mathematics. Since Ayer argued inLTL that onecannot be a good philosopher without understanding the propositions ofscience (later he even said that “if anything is to be achievedin the philosophy of physics, it must come from the inside”,1962, p. 15), he tried to mature in the natural sciences with the helpof his friend, J. L. Austin (see Rogers 1999, p. 130), but he quicklyended that project and continued to do research in his favorite topic,namely epistemology.

AlthoughLTL itself, for which Ayer is most well-known amongAnglophone philosophers, hardly contains radically new insights anddevelopments in logic, philosophy of mathematics and scienceperse – things for which the Vienna Circle is known asrevolutionary – Ayer’s oeuvre, as we shall see below,contains important details and considerations that earned him aleading place in the history of analytic philosophy (about that seeQuinton 1991, and the studies in Tuboly 2021a, especially Vrahimis2021).

2.3. Philosophy and Metaphysics

If logical positivism is known for one thesis, then it is therejection of metaphysics as literally and cognitively meaningless (seeCarnap 1932/1959, and Section 3.1 of the entry on theVienna Circle). Following the Vienna Circle, Ayer also developed distinctanti-metaphysical views, for which, as he stated in a letter to OttoNeurath in 1935, he was “made to suffer economically”because “at Oxford … metaphysics stillpredominates” (quoted in Tuboly 2021b, p. 4, n. 3). Ayer triedto “demonstrate the impossibility of metaphysics” alreadyin 1934 and by following Carnap, he argued that statements ofmetaphysicians are not uncertain, arbitrary, or unclear, but entirelynonsensical, stemming from linguistic or grammatical mistakes andemotional extrapolations (Ayer 1934a, 342). Although a series ofcritical discussions developed from this paper (see C. A. Mace 1934a,1934b, Ayer 1934b replying), his views did not change much inLTL where Ayer tried to “eliminate metaphysics”.Utilising his “criterion of verification”, he went on toargue that only verifiable, that is, empirical propositions aremeaningful (see below Section 3.1.), and since metaphysical statementspurports to describe a non-empirical realm, they cannot be verifiedneither practically, nor in principle, thus they lack cognitivemeaning (LTL, p. 37).

At this point, Ayer did not use or rely on Carnap’s positivestory about metaphysics (see, for example, Damböck 2024), namelythat even if metaphysical statements lacks cognitive meaning, that is,they do not express truth-apt empirical propositions, they still havean important existential function by expressing our attitude towardslife. This view of metaphysics was taken by Carnap mainly from WilhelmDilthey and Friedrich Nietzsche, thus from continental sources sourcesthat were mainly either unknown or seemingly unimportant forAyer’s whose Anglophone sources and problems were often incontrasts to Carnap’s original German-speaking cultural andscholarly environment (on thatsee Vrahimis 2021). Furthermore, themore positive and practical approach to metaphysics resonated wellwith certain pragmatist ideas about the usage of concepts, languageand theories and how they relate to social matters, which wasrecognised later both by Carnap and by another prominent logicalempiricist, Philipp Frank (2021, p. 271) who provided a Dewey-inspiredbehaviorized account of Carnap’s critique of metaphysics. Assoon as Ayer got involved more and more with traditional pragmatism,he also started to develop his similar, more positive account ofmetaphysics, especially in philosophy of science and meaning.

Ayer took his clue from C. S. Peirce (about the importance of use inmeaning, see Ayer 1968) and more directly from one of the last papersof Frank Ramsey, “Theories”, in which Ramsey (1929/1965,pp. 212–214) differentiated the “primary system”(corresponding mainly to the observational language of a theory) fromthe “secondary system” (which is the non-observable, ortheoretical language). The first one is related by Ayer to the factualcontent of theories, developed out of primitive data of perception,the heritage of common sense. The primary system consist ofdescriptions of physical things that are identified with series ofevents, which constitute their histories: “such and suchobservable properties are located at such and such particular placesat such and such particular times” (1973, p. 142). These weresupposed to register facts of the matter, hopefully in an atomisticmanner (coming from his Humeanism).

But there were various problems with a simplistic atomist conceptionof facts, entirely graspable within a primary system that is sharplydistinguishable from the secondary system. Ayer accepted (in fact,already inLTL, pp. 38–39; cf. Glock 2021, pp.267–268) that a theory has to be tested as a whole and “wemay have latitude in deciding which parts of it there is need torevise” (Ayer 1973, p. 29). Because of that, a theory as a wholeanswers to experience and it becomes hard to decide which part of itis purely formal and which have factual content. Furthermore, byreferring to Hempel’s “The Theoretician’sDilemma” (1958), Ayer argues that quantitative concepts ofscience cannot be defined “in terms of what is actuallyobservable” (1973, p. 32), and thus experience and observationcannot match the ‘openness’ of the texture of scientifictheories. From a more general linguistic point of view, Ayer gave somecredit to the view that “we take at least as much interest inthe way things come into being and in the uses to which we can putthem as we do in the perceptible properties by which they areimmediately recognized”, (1973, p. 141), that is, our conceptsof things are implicitly related to different concepts, like that of“being an oak” to “sprung from acorn”, thatis, even statements of factsseem to point beyond themselves.Although he provided a detailed criticism of this view (by saying thatwhat happens in such cases is that we build a causal generalisation– that oaks stem from acorns – into the definition of theterm and try to secure it that way, see 1973, p. 141), he conceivedmore positively a similar issue in a different context. Statements ofcausation, writes Ayer, are partially dispositional because they covernot just actual, but also possible correlations, by saying that underthese and these circumstances (independently whether they are actuallyhappening now or not), such and such a event will happen. Thus, causalstatements always involve some kind of generalisation (not necessarilya law, but a regulation, to save Hume’s insights), like“one event would not occur unless another event stood in suchand such a spatio-temporal relation to it” (1973, p. 144). Butbecause of these considerations, the primary system, or the observablelanguage, is not just way too austere, but conceived facts toonarrowly.

Beyond the “primary system” is the “secondarysystem” that “legislates for possible as well as actualcases and can also contain terms which are not directly related toanything observable” (1973, p. 33; Ayer refers here back toPeirce and compares the secondary system to what Peirce’s idealof “the arrangement of facts”). While primary systems register factsand contains thus only factual propositions, secondary systems couldbe extended to cover possible and fictitious cases as well. Theirfunction is thus “explanatory” and their goal is toarrange primary facts as conceptual tools (1973, pp. 109–110).As Ayer put the point in a related paper, facts of the world(described in the primary system) could be arranged and make sense indifferent “conceptual systems”. He used LudwigWittgenstein and Arthur Eddington’s simile, “we spread thenet, but we have to wait and see what it catches” (1962, p. 19).With different nets (secondary systems), different facts can begrasped (in the primary system), and it is philosophy’s task todeal with these secondary systems (see Section 2.1. above). Because ofthat, Ayer became more permissive with metaphysics, itself aconceptual system, and argued that “we are, I think, entitled torequire of any metaphysical theory that it should function as asecondary system, at least to the extent of having some explanatoryvalue” (1973, p. 33). Metaphysics could thus serve as a tool toarrange facts and reshape experience and our relation to the world.Since the boundaries between primary and secondary systems seem to bearbitrary and our actual primary system was “itself the productof theory” (1973, p. 144), philosophy, and with it metaphysicstoo, can “formally” change the world “byrefashioning the structure of language. In this way it may help todetermine what facts there can be” (1962, p. 19). (OnAyer’s changing attitude towards metaphysics see Körner(1979), to which Ayer (1979, ) replied, to which Körner (1991)also replied in more details.)

3. Meaning and Truth

3.1 Meaning

The empiricist basis of Ayer’s attitude to meaning was laidfirst in his reading of Hume. The thought that no idea had anyempirical significance unless it was suitably related to an impressionstayed with him, and was reinforced both by his reading ofWittgenstein’sTractatus and by the time spent inVienna with the Logical Positivists. His first formulation of acriterion of meaning, the principle of verification, was in the firstedition ofLTL (1936), where he claimed that allpropositions were analytic (true in virtue of their meaning) or elseeither strongly verifiable or weakly verifiable (a differentreconstruction of Ayer’s view of analyticity and a defenceagainst some of its critics are presented in Rathgeb 2021). Strongverification required that the truth of a proposition be conclusivelyascertainable; weak verification required only that an observationstatement be deducible from the proposition together with other,auxiliary, propositions, provided that the observation statement wasnot deducible from these auxiliaries alone. This rapidly proveddefective: any propositionP conjoined with ‘ifP thenO’, where ‘O’ isan observation statement, will yieldO, without this beingdeducible from ‘ifP thenO’ alone. Soin the second edition Ayer amended the principle to read: a statementis directly verifiable if it is either an observation statement or issuch that an observation statement is derivable from it in conjunctionwith another observation statement (or observation statements), suchderivability not being possible from the conjoined observationstatement(s) alone. And a statement is indirectly verifiable if,first, in conjunction with certain other premises it entails one ormore directly verifiable statements that are not derivable from theseother premises alone, and, second, that these other premises “donot include any statement that is not either analytic, or directlyverifiable, or capable of being independently established asindirectly verifiable.” (LTL 2^nd ed. P.17).

This principle generated further criticism, most significantly fromAlonzo Church (1949), who claimed to show that, again, it allowedany statement to be meaningful. TakeO₁,O₂, andO₃ as logicallyindependent observation statements, andS any statementwhatsoever. Then

(1) (¬O₁&O₂) v(O₃&¬S)

is directly verifiable, as (1) in conjunction withO₁ entailsO₃.Sbecomes indirectly verifiable, asO₂ follows fromS and (1), and (1) is directly verifiable. ShouldO₂ follow from (1) alone, thenO₂ follows fromO₃&¬S, which means that¬S is directly verifiable (O₂ andO₃&¬S being logicallyindependent).

Despite the failure of these attempts to provide a rigorous empiricistcriterion of meaning, Ayer continued to hold that there was a closeconnection between evidence and meaning, maintaining that asatisfactory account of confirmation was needed before a fool-proofcriterion of empirical meaning could be supplied. Given later doubtsabout whether any theory of confirmation could provide a foundationfor a theory of meaning (Quinean doubts relating to the impossibilityof ruling out any facts as possibly bearing on the truth of anysentence), it remains unclear as to how the evidence-meaningconnection can be circumscribed. (For a review of other attacks on,and adjustments to, the verification principle, see Wright 1986, 1989;for a recent evaluation, see Glock 2021.)

In addition to the technical difficulties surrounding the properformulation of the meaning-criterion, Ayer later acknowledged that hehad been vague as to whether the criterion was intended in a‘weak’ or ‘strong’ sense: if weak,verifiability merely demarcated sense from nonsense, whilst the strongversion meant that the method of verification provided the meaning ofthe sentence. It was the strong version that was used in hisdiscussion of the meaning of sentences about the past and other minds,but in his discussion of the latter another difficulty emerged. It hadnot been made clear whether the ‘method of verification’was intended to be neutral between people employing the sentences inquestion, and so provide a standard meaning for these sentences, orwhether such a method could provide an idiosyncratic meaning for oneindividual’s use of the sentence, the method of verificationbeing peculiar to that person. In his discussion of mentalexperiences, Ayer had implicitly taken the second route, and sosentences attributing such experiences to himself were given a‘mentalistic’ analysis, and those attributing experiencesto others were given a behaviorist analysis in terms of theirempirical manifestations, namely with reference to their overtbehavior (see the introduction to the second edition ofLTL,and also the work of Uebel (2021) who shows not just how Ayer’sposition has changed about the various arguments about the existenceof other minds and the mental-state attribution to others, especiallythe so-called argument from analogy, but also how Ayer’s ownphilosophical estimation between his various works evolved and gotscrutinized). At the same time, however, he construed another’sself-attribution of experience mentalistically, whereas, as he lateracknowledged, to be consistent these should also have been given abehaviorist analysis (see the discussion between Bernard Williams andAyer in Macdonald 1979; for a general reconstruction of Ayer’sphilosophy of the mind-body problem, see Ambrus 2021).

The strong interpretation of the criterion required there to be somedecision made as to what evidence contributed to the meaning ofverifiable sentences. For Ayer it was clear that not all evidence fora statement was to be included in the meaning of the statement: astatement about the blood on Jack’s jacket was not included inthe meaning of the assertion that Jack was the murderer. Further,although only present evidence is available to anybody making astatement about the past, the meaning of such a statement is notrestricted to such present evidence; one is entitled to include in themeaning evidence that would be available if one were able to transportoneself to that past time. Moral statements were, in Ayer’sview, not verifiable, and so could not be construed as assertions offact, being interpreted instead as expressions of emotion. This isexamined again in Section 8.

The only class of statements that Ayer allowed to be meaningfulwithout such a connection to evidence was that comprised oftautologies, which included all analytic propositions. These were theonly propositions knowablea priori, their meaning beingdependent on how language was used, and on the conventions governingthat use. Ayer insisted that the necessity attaching to thesepropositions was only available once the conventions governinglanguage-use were in play.

3.2 Truth

When discussing the problem of truth, Ayer distinguished between twofundamental questions – “What is truth” could beread as “What istruth?” and “Whatis truth?”. In the first case, we deal with the definition of“truth” and discuss that common property that is shared byall true entities. This is a definitional project about the nature andcharacter of truth. In the second case, however, we have to clarifywhat or which entities – mostly proposition, statements, orsentences – are true (and are false). This question concernsthat criterion, or in certain cases, the criteria of truth. As Kocsis(2021) has shown, Ayer (1935) was very much aware of this distinctionthat was formulated back then by two of his philosophical heroes,Bertrand Russell (1910, pp. 172–173) and Frank Ramsey(1927–29/1990, p. 6).

InLTL Ayer, following Ramsey (as he thought, but see Field1986 for a dissenting view), put forward a redundancy (deflationary)view of truth: “…in all sentences of the form‘p is true’, the phrase ‘is true’ islogically superfluous” (LTL p. 117). The function ofsuch a phrase is simply to mark an assertion (or denial, in the caseof ‘is false’), so there is no ‘real’ relationof truth, and so no problem of truth for philosophers to worry about.Similarly, when we say a proposition is probable, or probably true, weare not assigning any intrinsic property to the proposition, norsaying that there is any relation it bears to any other proposition.We are simply expressing our confidence in that proposition, or, moreaccurately, it expresses the degree of confidence it is rational topossess in the proposition. Note, however, that afterLTL,Ayer (1992) realized the need for a less radical and moresophisticated deflationary view about the nature of truth,“admitting that in exceptional cases, the usage of the truthpredicate is unavoidable” (Kocsis 2021, p. 290).

About the criterion of which statements are true, Ayer held a moresubstantial view. He formulated his approach within the ViennaCircle’s famous protocol-sentence debate (Uebel 2007), where thetwo basic position about the criterion might be labelled “coherentism”and “correspondism”. According to coherentism (defended by Carl G.Hempel and Otto Neurath), protocol sentences cannot be compared withreality, and their truth consists in being members of a coherentsystem of propositions. Correspondists, like Moritz Schlick, thoughtconsistency itself cannot furnish a sufficiently strong criterion(fairy tales, for example, can be consistent too), and the criterionof truth lies in a protocol sentence’sagreement withempirical reality. Ayer sided with the correspondists in arguing thatthe criterion of truth in empirical matters is the comparison of thegiven statement with empirical reality. Because of that, Ayer deniedthat moral utterances were truth-apt. Given that he thought thatasserting thatp was equivalent to saying thatp wastrue, and that there should be a strong agreement between a statementand its empirical correspondent, he had to deny that moral utterancescould be assertions (see section 8).

Nonetheless, Ayer was “a false friend to Schlick” (Kocsis2021, p. 297) because he argued that “there are no finalproposition” (LTL, p. 94), contrary to Schlick’sviews, and all our empirical propositions are just hypothetical andrevisable through and through (just as Neurath thought). By comparingpropositions with reality, we are aiming at truth by formulatingpredictions about future experiences that could be fulfilled and thusnominated as truths. “The main difference between Ayer andSchlick,” argues Kocsis (2021, p. 299), “is that Ayerpursued and provided an authorizing criterion, while Schlick aimed ata guaranteeing criterion of truth.”

This deflationary attitude to truth was supported by hisverificationism about meaning; Ayer did not have to providetruth-conditions for the meaning of sentences. Assertions had meaningin virtue of their verification conditions, and propositions weredefined just as an equivalence class of sentences with the sameverification conditions.

See the entry onthe deflationary theory of truth for further discussion.

4. Perception

In his early work on perception Ayer espoused a strict form ofphenomenalism, defending the view that statements about materialobjects are translatable into statements about actual and possible‘sense-contents’. These latter statements were theultimate verifiers, forming the basis upon which our empirical worldwas constructed. Although he later abandoned the reductionism inherentin the translatability requirement (beginning with“Phenomenalism” in 1947), believing that he had been wrongto think that any statement about a physical object could be entailedby a set of statements about sensory experience (sense-data), Ayercontinued to hold that our claims about physical objects werejustified by reference to such sensory experience. He consistentlyopposed the view, espoused by Rudolf Carnap, Otto Neurath, and KarlPopper, that the only justifiers were sentences, whetherNeurath’s ‘protocols’ or Popper’s ‘basicstatements’. His criticism of such views was that the favouredclass of statements could not be picked out in the right way withoutan appeal to relevant experience. So a criterion for membership of thefavored class of statements that required only those statementsaccepted by the scientists of the time to be members of the class wasnot going to be successful without knowing which sentences were thusaccepted, and this, Ayer claimed, could only be known by experience.The alternative of using yet another sentence, one stating that these(p,q,r, …) were the sentences in therelevant class (those accepted by the scientists), would make thefoundations of science entirely arbitrary.

Even on Ayer’s later view, called ‘sophisticatedrealism’(in Ayer 1973), where our perception of physical objectswas indirect, the ultimate bases for perceptual judgments weresense-data, which were now called ‘qualia’ (or, ifparticularized, ‘percepts’). It was this continuingcommitment to sense-data as the objects of perception that drew J.L.Austin’s (often sarcastic) criticism inSense andSensibilia (1962). On Ayer’s view, qualia formed thepatterns constituting a primary system, and it was on the basis ofthis system that we posited the existence of physical objects, thisbeing the ‘theoretical’ secondary system. Once we havethis theory, we are able reinterpret the quale as mental states andclaim that they are caused by the physical objects. This causal claimis only merited once the theoretical system is in place, and so cannotbe a primitive element in any account of perception. The physicalobjects are required to be there before any causal hypothesisinvolving them makes sense.

Part, but only a part, of Ayer’s reason for embracing suchindirect realism was what has been called the argument from illusion,the central idea of which is that, for any perceptual state of ours,we could be in a state indiscriminable from it but which did notinvolve perception of any material object or scene, it being anillusion that there was any such object or scene to be perceived. Thatis, non-veridical perceptions could share their intrinsic propertieswith veridical perceptions, this possibility leading Ayer to claimthat it was plausible that the object of perception in both cases was(non-material) experience, and not, as naïve realism would haveit, the physical objects themselves. As a consequence, ordinaryperceptual judgments, those making claims about such objects, gobeyond what is ‘strictly available’ in our perceptualexperience, and so they form a theory about that which is available toperception.

There are many ways of querying Ayer’s conclusion. Austinattacked the way he saw the argument from illusion being deployed. Hequestioned just about everything in it: the distinction betweenveridical and non-veridical perception, the supposed generalizationfrom ‘some (real) perceptual experience is indiscriminable froma (mere) perceptual appearance’ to ‘all such perceptionsare indiscriminable from their counterpart appearances’, and theassumption that when we have defective perceptions there arenon-material objects of those perceptions, sense-data.

Strawson (1979) argued that the primary system, that purporting todescribe no more than what was ‘strictly available’ toperception, could only be described using concepts available to thosealready acquainted with the secondary system. A consequence of this,he claimed, was that the secondary system embodied in ordinaryperceptual judgments could not be a theory with respect to which theprimary system was the data – the data have to be describable interms that do not presuppose the very theory for which they are thedata. Although, he argued, it may be possible, though difficult, forus to strip our vocabulary describing our experience of suchsecondary-system concepts, such an effort on our part would beunusual, and not at all like what is involved in our common-senseperceptual judgments, those that Ayer supposes to be the result ofsome theorizing on our part. For Strawson, our commitment to aconceptual scheme of a realist character is ‘something givenwith the given’ (Strawson 1979, p. 47).

Ayer was unmoved by the objections. He replied to Austin’sattack in “Has Austin Refuted Sense-data Theory” (Ayer1967), with Ayer defending the viability of the distinction betweenveridical and non-veridical perception, and maintaining that theargument from illusion was only one source of the case for sense-data.(For an in-depth discussion of the dispute between Austin and Ayer,see Mike Thau, “What is Disjunctivism” 2004). AgainstStrawson (“Replies” 1979) he noted that there wasconsiderable agreement between them: in particular, they both agreedthat perceptual judgments contain implications going beyond thosecarried by a ‘strict’ account of our sensible experience.The disagreement was primarily about whether the perceptual judgmentswere based on, or were inferred from, awareness of sense-data. Ayerconceded that such an inference would be only implicit. The pointabout language he conceded as well, maintaining only that theassumptions often built into concepts descriptive of physical objects– the accessibility of such objects to other observers, thatthey continued to exist unperceived, and so on, would not be in playwhen these concepts were used to provide the ‘strict’account of perceptual experience.

5. Induction and Probability

Hume was an influential figure in the formation of Ayer’sphilosophical views, so it is no surprise to find Ayer’sapproach to inductive inference modeled on Hume’s. Ayer definedinductive inference in negative terms, as involving all factualinference in which the premises did not entail the conclusion. Allsuch inferences, Ayer claimed, presumed the uniformity of nature, anassumption he put in terms of assuming that the future will, inrelevant respects, resemble the past (1956, p. 72). To unambiguouslycover cases of retrodiction, the assumption is better put in terms ofthe unobserved resembling, in relevant respects, the observed. Ayeragreed with Hume that relying on any ‘principle’ of theuniformity of nature was not going to help justify inductiveinference, given that such a principle was itself not demonstrable. Asimilar argument applied to any other principles that may have beenthought to supply the missing ingredient, such as an appeal touniversal causality, or to laws of nature. These were also notdemonstrably true, so would require justification themselves, and anyappeal to these principles in such a justification would be viciouslycircular.

The fundamental problem here is that the inductive gap can be closedonly if the premises can somehow be made to entail their conclusion,and Ayer denied that this could be done. Naïve realism tried todo it by making the evidence ‘move up’ to the conclusion– by making it the case that in perception our evidence wasdirectly of physical objects, rather than of sense-data from whichphysical objects were inferred. This could work, if it did, only forperception, and not for other inductive inferences. Reductive attemptsto close the gap tried to make the conclusion ‘move down’to the premises, as in phenomenalism. Ayer by now thoughtphenomenalism was unsuccessful in this attempt, and again reductionismwould not work for the future cases. In his 1956 he thought that thebest we could do was to admit the gap and be content to describe theways in which we actually went about justifying such inferences.

Ayer went on in later work to examine the problem of induction ingreater detail, in particular in relation to attempts to make theproblem tractable by appeal to notions of probability. In 1957 hewrote an important article attacking the idea that the logicalconception of probability could be a useful guide to the future. Givena proposition,a, that a horse is going to win the race, andvarious sources of evidence,h₁,h₂,h₃…h_n, one can estimatethe probability ofa givenh₁ to bep₁, givenh₂ to bep₂, and so on. One can also estimate theprobability ofa given all ofh₁…h_n. Call this probabilityp_n, it being the probability ofa givenall of the evidence available to the person wishing to place a bet onthe horse. Which of these probabilities, asks Ayer, would it berational for this person to base their bets on? Common sense dictatesthatp_n is the best estimate, but Ayer argues thaton the logical conception of probability, all of the estimatesp₁…p_n are logicallytrue, and so it is impossible to single out one as being‘better’ than any of the others.

Ayer notes that common sense (and Carnap) say that a probability basedon ‘total’ evidence is what is needed. But why do we haveto take into account total evidence? Given that all of the differentestimates are logically true, there can be nothing wrong in relying onone rather than another. Saying that if one takes into account all theavailable evidence one is more likely to be right is equivalent tosaying that the hypothesis that ‘those with totalevidence’ are more often right has a certain probability, andthat gets us no further forward. Ayer took this result as a reason toreject the logical interpretation of probability statements, arejection repeated in his more extended treatment of probability inProbability and Evidence 1972, and again in his reply to J.L.Mackie’s attempt to rebut his objections (see Mackie 1979, Ayer1979).

InProbability and Evidence Ayer also criticised thefrequency interpretation of probability, noting that under thisinterpretation the probability of an event will change with any changein the reference class to which that event is assigned. The frequencyinterpretation itself cannot determine whether the choice of onereference class over another is better for the determination of therelevant probability, and so suffers from a critical defect if it isto be of any use in solving problems associated with inductiveinference. (For further discussion of Ayer’s views onprobability and induction see Bela Juhos 1969, and Foster 1985, pp.198–227.)

6. Knowledge

InLTL, Ayer was less concerned with the traditionalepistemological questions that came to dominate his thought in theforthcoming years in such works asThe Foundations of EmpiricalKnowledge (1940) andThe Problem of Knowledge (1956).The most relevant parts of the early work concern the question ofcertain and fallible knowledge in empirical matters. Ayer explicitlyrejects the idea (coming from Moritz Schlick and Béla Juhos ofthe Vienna Circle) that there would be any empirical statement that isabsolutely certain and indisputable, like ostensive propositions thatpurport to record direct perceptions or observations. Ayer thoughtthat empirical statements always contain descriptive and conceptualelements (LTL, pp. 90–91), and thus they can’t beabsolutely certain – there are no pure registrations ofone’s experience. Because of that, every empirical propositionis revisable as a hypothesis, and “may be confirmed ordiscredited in actual sense-experience” (LTL, p.94).

Experience has the final world in our empirical knowledge (if onestates that experience can’t refute a certain purportedlyempirical propositionp, thenp is simply adefinition in disguise, seeLTL, 95), and thus, anticipatingwhat later made famous by Quine, Ayer argued that “the’facts of experience’ can never compel us to abandon ahypothesis. A man can always sustain his convictions in the face ofapparently hostile evidence if he is prepared to make the necessaryadjustments hoc assumptions” (LTL, p. 95). But thedetails of how exactly one can handle empirical evidence, how normsand reasons shape them, and how to counterweight various skepticalstrikes, Ayer had to engage more deeply with traditional epistemology.By the mid-1930s, Carnap has just tried to convert epistemology intopure logic of science (see Uebel 2018) but Ayer did not follow him,thus he started to diverge from major concerns of (at least somerepresentative) logical positivists early on.

InThe Problem of Knowledge (1956), Ayer defended acontext-based account of knowledge that had as its essentialingredients that some claim,p, counted as knowledge for aperson,A,iffp was true, A was sure thatp, andA had, in the relevant context, ‘theright to be sure’ about the truth ofp. The contextualelement is apparent in the discussion after Ayer outlines what isrequired to have the ‘right to be sure’ in themathematical case. One avenue to knowledge in this case lies in theability of the agent to provide a proof of the relevant proposition.In the case of perception, or memory, it is clear that it isimpossible to possess such a proof, so a more relaxed standard isrequired. To statein general how strong the backing needs tobe for a believer to have the right to be sure that their belief istrue is not possible; doing so would require drawing up a list ofconditions “under which perception, or memory, or testimony, orother forms of evidence are reliable.” (1956, p. 32.) Ayerthought this would be too complicated a task, if at all possible. The‘correct’ standard to set for claims to knowledge is to bedecided pragmatically, on grounds of practical convenience. Theskeptic’s ploy of setting an impossible standard, one requiringthe impossibility of error, should be resisted, as one has the rightto be sure even where error is possible. (Ayer discussed such apragmatic view of vindication later in the context of scientifictheories too, when he wrote that “we hold fast to our theoriesbecause we find that they work, even though they do not satisfy thesceptic’s standards of proof”, 1973, p. 137.)

The account offered was intended as an analysis of knowledge, butrevealingly Ayer did not require that believers be aware of how theyhave the right to be sure. It was allowed that somebody who invariablycorrectly predicted the outcome of a lotterycould be said toknow that their prediction was true, even though they, nor anyoneelse, had any idea of how the predictions came to be reliable. Ayeradmitted that this case, and others like it, may cause some dispute:it was not clearly covered by the meaning of the term‘knowledge’, and so left room for some stipulation.

Ayer’s particular analysis, or one closely resembling it, cameunder attack in a famous paper by Gettier (1963), in whichsatisfaction of the three clauses (the truth ofp, the beliefinp, and the right to be sure thatp) was held tobe insufficient for knowledge. Gettier’s argument requires thatsomeone,A, could be justified in believing a falseproposition, and that ifA was justified in believingp andq is deducible fromp, andAacceptedq by deducing it fromp, thenAwould be justified in believingq. An example used by Gettierhas the following structure: (i) Jones owns a Ford. (ii) Either Jonesowns a Ford or Brown is in Boston. Smith believes, and has ampleevidence for, (i). He deduces (ii) from (i), and so is justified inbelieving (ii), even though, in fact, he has no idea of where Brownis. It turns out that (i) is false, but (ii) is true –unbeknownst to Smith, Brown is indeed in Boston. Gettier concludedthat in this case all three clauses of the analysis of knowledge aresatisfied, but that we should judge in this case that Smith did notknow (ii). The suggestion was that additional clauses might beneeded.

The literature spawned by the Gettier counter-examples is huge, nearlyall of it attempting to pin down the elusive additional clause(s).Ayer himself did not think that any such additional clauses wereneeded. The counter-examples, he thought, showed that what was neededwas a more careful account of what ‘being justified’consisted in. He disputed Gettier’s claim that any deductionfrom a justified, but false, proposition preserves justification. Wealready knew, he claimed, that the notion of having evidence for aclaim is very difficult to elucidate; Carl Hempel’s paradoxessucceeded in showing that. Once we had managed to throw more light onthe justification relation, we would see that his proposed analysiswas sufficient for knowledge.

7. Necessity, Causality, and Freedom

We have seen that inLTL Ayer maintained that all necessarytruths were true in virtue of the meanings of the terms used inexpressing them, this in turn depending on the conventions governingthe use of those terms. One can see in the expression of this earlyview unease about the source of logical necessity. He describes thenecessity of logical truths as dependent on the rules governing theuse of logical constants. Although such rules are neither true norfalse, they elucidate the “proper” use of such constants,a formulation suggesting that the source of the necessity is deeperthan mere linguistic usage.

Later, cleaving (or perhaps clinging) to his “all necessity isde dicto” starting point, he consistently refused tocountenance anyde re necessities. He strenuously resistedthe essentialism that became fashionable following the work of Putnamand Kripke in the 1970s, but his reasons for doing so were not alwaysto the point. In his argument against essence-basedde renecessities Ayer would say that “Caesar is necessarilyhuman” is not true, since he could have called his dog“Caesar”. Here he lost sight of his own insistence (in theIntroduction to the 2^nd. Edition ofLTL) thatnecessary truths were expressed in a language whose terms had alreadybeen assigned meaning and reference, so changing the reference of“Caesar” is irrelevant to the necessary truth of asentence employing the term with its ‘normal’reference.

Of greater relevance was his suspicion of the move from conceivabilityto possibility, and inconceivability to impossibility, thinking thatanswers to questions about conceivability were dependent upon thestate of knowledge and imaginative powers of the person entertainingthem. Was it inconceivable that Caesar (the Julius of old) benon-human? Ayer thought it consistent with everything he knew ofCaesar (apart from his being human) that Caesar was a robot, so hecould “easily conceive of it as a possibility”(“Replies” p. 308). On the other hand, if asked whetherCaesar was a tortoise, he would suspect that the word“Caesar” was here used with a different reference in mind.Ayer buttressed this thought by suggesting that the descriptionssecuring the referent of the term “Caesar” would normallymake it logically inconsistent that the satisfier of the descriptionsbe a tortoise, but that this did not establishde renecessities; it does not follow that the Caesar in questionnecessarily satisfies the descriptions associated with theuse of the name. To the suggestion that something other thandescriptions might secure the proper reference, such as the causalorigin of the use of the term, Ayer was dismissive: “…theidea …that one can explain the nature of reference by sayingthat what makesA’s use of a signs areference to an objectO is its causal derivation fromsomeone’s original use ofs to refer toO is amanifest absurdity. If one does not understand what it is fors to refer toO, one is none the wiser; and if onedoes, the causal flummery is otiose.” (“Replies”1979 p. 309.)

Ayer’s rejection of these kind ofde re necessitieswas, at root, a consequence of his epistemological approach to theirevaluation. The senses of terms, he thought, were dependent on theirassociated descriptions, these being dependent on what we knew oftheir reference, and these senses accounted for the presence orabsence of necessity. So it is identity of sense in “Hesperus isHesperus” that makes that sentence necessarily true, whilstabsence of sense-identity renders “Hesperus isPhosphorous” contingently true. He rejected the thought thatnatural kind terms have their sense fixed by their internalconstitution on the grounds that many, if not most, users of naturalkind terms are ignorant of the nature of the relevant internalconstitutions. In this he is in agreement with those who recognize thekind of necessity arising from primary intensions (Chalmers 2004) or‘A intensions’ (Jackson 1998), such intensionsbeing determined by (some) phenomenal properties of the kinds referredto.

Ayer also repudiated causal necessity. Following Hume, he thoughtcausation could be reduced to regularity: “c causese” is equivalent to “wheneverc thene”. This latter proposition is then a law of nature,which is just a generalization to which we have a certain attitude. Socontingent generalizations and laws of nature are much the same; theydiffer only in that we rely on the latter more than the former, andare prepared to treat the law as though it possessed some strongermodality, though in fact it does not.

The lack of necessity attaching to causes made Ayer’s acceptanceof human freedom undemanding. Having denied the existence of anycausal necessity it was open to Ayer to be a compatibilist:determinism could be true (all action could be caused), but one couldstill accept that this left it open as to whether the agent could havedone otherwise, given that the existence of the cause did notnecessitate the action. Ayer argued that the relevantcontrast to freedom was not causality, but constraint, or compulsion,which are a ‘special’ sort of cause. So if our actionscould be caused whilst not being ‘constrained’ in any way,then determinism could be true and we could still be free. It was justas well that this position was available, claimed Ayer, because beingheld morally responsible for our actions required that these be notthe result of sheer chance.

This leaves, as Ayer recognized, a problem: if freedom is possiblebecause causes don’t necessitate, then am Ieverunfree? Ayer’s reply was straightforward. It is only some causesthat deprive us of freedom; if a robber puts a pistol to my head anddemands my money, he has left me without a reasonable alternative, soI am not morally responsible for the action I am made to do. So to saythat I could have done otherwise is just to say that I would have doneotherwise had I so chosen, that my action was voluntary in the way inwhich the kleptomaniac’s isn’t, and that nobody compelledme to act in the way that I did. (See “Freedom andNecessity”, 1954). This ‘resolution’ of the problemremains unsatisfactory; Ayer’s type of compatibilist does nothave an acceptable account of why it is that some causes aresufficient to make my action not free, whilst others contain no suchthreat. As he says, all causes are equally necessitating – noneof them necessitate, not even the ‘special’ sort of causesthat, he alleges, threaten our freedom.

8. Ethics

The emotivism espoused by Ayer inLTL was supported by hisbelief in the distinction between fact and value. Given, he thought,that there were no moral facts to be known, there could be noverification of such facts, and so moral utterances could have nocognitive significance. And given the connection between moral‘judgment’ and motivation, and the connection betweenmotivation and feeling, it was natural to see moral utterances ashaving the function of expressing our feelings, or‘emoting’. This view, Ayer was careful to point out, wasnot that associated with subjectivism, that in making moral claims wearedescribing our feelings. This latter view would makemoral claims truth-evaluable, and Ayer’s moral emotivism deniedthat they were so evaluable. So when we say: “Cruelty towardschildren is wrong” we are really expressing a negative attitudetowards killing children, and when we say “Being kind to oldpeople is good” we are expressing positive feelings towards suchacts of kindness. The expression of such positive or negativefeelings, he later thought, also contained a prescriptive element, soin such expressions we are also encouraging others to share thosefeelings, and to act accordingly. As this makes clear, the attitudesexpressed were towards classes of acts, and not particular acts.

Emotivism was thought by some to be thereductio ad absurdumof the verificationist theory of meaning, and indeed it was not thepreferred metaethical position of other positivists, some of whompreferred a consequentialist approach, and so emotivism could be seenas separable from verificationism. In fact, in the“Introduction” to the second edition ofLTL Ayerstated that his commitment to emotivism would survive any demise ofhis positivism, and it later became clear that it was because Ayerthought moral judgments to be not fact-stating that he concluded theywere unverifiable (see “The Analysis of Moral Judgments”in Ayer 1954). Emotivism was given additional support byC.L.Stevenson, who had developed his ideas independently of Ayer, inhis bookEthics and Language (1944). In subsequent decades,it spawned a family of what came to be called“expressivist” views in metaethics, which sought to statethe view with a sensitivity to the logical problems Ayer’sformulation raised.

It has been suggested (Dreier 2004) that Ayer faced a particulardifficulty in defending this brand of non-cognitivism; the combinationof affirming a redundancy theory of truth with the denial that moralclaims can be true looks suspicious. Although the two views are notincompatible (Ayer denied that moral claims were assertions, and theredundancy of the truth-predicate held only for assertions), thetension between the two is symptomatic of the worry that moral claimshave so many of the features of truth-evaluable assertions that onehas to be unjustifiably revisionist in construing them asnon-meaningful. They are, after all, typically expressed in indicativesentences, and people appear to dispute moral claims. This latterpoint Ayer did respond to: moral disagreements were, he (andStevenson) claimed, either genuine disputes about non-moral facts, orsimply not genuine disagreements. (For an examination of the troublethat moral disagreement makes for emotivism, see Smith 1986.) Therewas, however, a further, more troubling, point about the role of moralterms in arguments: moral terms can be used in arguments in which themoral term appears in a conditional, and so is not there contributingto the expressive force of the utterance, so not expressing anyemotion of the speaker. This latter point has been developed into aline of reasoning (called the “Frege-Geach” problem)against expressivism in general. The problem for the expressivist isto make sense of simple arguments such as the following: (1) If Johnkilled Jane, he did something wrong. (2) John killed Jane. So (3) Johndid something wrong. The argument appears to be valid, and so not toinvolve any ambiguity, but the moral term can be construed as havingexpressive force only in (3), not in (1). Expressivism, and soemotivism, seems to introduce an unwarranted equivocation into theargument.

It is perhaps these ‘surface’ features of moral discourse,those that make it look like moral claims are assertions, and henceexpressions of belief, and so truth-evaluable, and that moraldisagreement appears to be genuinemoral disagreement, thatlater tempted Ayer to consider Mackie’s ‘error’theory of moral language (Mackie 1977) as closer to the truth (in Ayer1984). The details of emotivism tended to disappear from themetaethical scene in the latter half of the twentieth century, but itsguiding thoughts have remained very much alive in the expressivism ofBlackburn 1984, 1998, and Gibbard 1990. (See Altham, 1979, for asympathetic defense of these guiding thoughts, and Schroeder, 2010,for a thorough treatment of the development of expressivism, withparticular attention paid to subsequent attempts to tackle theFrege-Geach problem. In the context of Ayer, Pete (2021) has suggestedrecently – replying to Schroeder (2010) – aBerkeley-inspired modification of ethical and religious emotivism toarrive at quasi-realist, compositional semantics that could providedescriptive-representational content both for descriptive andnormative statements, in embdedded occurences as well to meet theFrege-Geach problem.)

From a more general point of view, Ayer was the target of variousfierce criticisms because of his ethical emotivism that was oftenlabelled as “nihilism”. In 1948, for example, Ayer wasattacked on the pages ofThe New Statesman and Nationmagazine by Giles Romilly (1948) under the pseudo name“Oxonion” (Romilly, a nephew of Winston Churchill,attended Oxford in the 1930s and thus witnessed howLTLthrilled the public and the university). He argued that Ayer’sview inLTL about ethics were partially responsible for theincreasing Fascist attitudes at the University of Oxford after theSecond World War by creating a vacuum of moral values. Romilly’scharges were taken up by C. E. M. Joad (1948 and 1950), a famous andwell respected public intellectual and philosopher of the 1920s and1930s.

Joad argued that logical positivists, especially Ayer, induced theerosion of morality by questioning its rational foundations. Afterdeclaring all of moral discourse to be meaningless, there remained nostandpoint for positivists from which certain behaviours and beliefs(like the democratic ones) could be declared right or better thanothers (like the Fascist ones). Furthermore, according to Joad,because of his anti-metaphysical sentiments, Ayer could talk onlyabout individual Fascists and not about fascism as a theoretical andabstract system or set of propositions and beliefs, although ameaningful, deep, and engaging public discourse requires that level ofabstract discussion. In a nutshell, Joad formulated a generalcriticism of logical positivism’s possibility to develop asocially engaged and practically relevant philosophy (of science) forsociety.

Ayer responded to Joad by emphasizing that the separation of“statements of facts” and “statements ofvalues” means that it is the Fascists who commit a logicalfallacy when they try to infer values from alleged facts. In addition,as logical positivism repudiates metaphysics and “Fascists havehitherto tended to favour some form of metaphysics” (Ayer 1948,30), Ayer denied thatLTL provided the foundation for Fascismin Oxford. About Joad’s second criticism, Ayer had less to say(on the logical empiricists attitude and socio-politically engagedphilosophy, without much reference to Ayer, see Romizi 2012, andrecently Damböck 2022). As Ayer recalled later in hisautobiography, when he had to teach social and political philosophy,his logical toolkit betrayed him:

“[p]art of the trouble was that my philosophical weapons wereunsuited to the purpose. Political concepts like those of the socialcontract, the common good or the general will did not repay minuteanalysis ad I had nothing original to put in their place.” (Ayer1977, p. 184)

As noted above (Section 1), Ayer was deeply involved in politicsduring his whole life, and he considered it as a practical matter,where his logical positivism does not have much to do with (for moredetails of the Joad-Ayer-debate, see Tuboly 2020). He thought thatBritish political thought was naturally progressive without deeppressing need of theoretical ramifications and justifications, incontrast to its continental, socio-politically engaged philosophicalcounterpart. As he summarized his stance in “Philosophy andPolitics”:

“I do not really feel the need for anything to replace thismainly utilitarian, mainly tolerant, undramatic type of radicalism.For me the problem is not to devise a new set of political principlesbut rather to find a more effective means of putting into operationthe principles that most of us already profess to have.” (Ayer1969, p. 260)

Combining his belief in freedom of the will with a thoroughgoingfallibilism and revisionism about empirical matters that required afull-blooded theory of knowledge, Ayer pursued a systematic philosophyfor theoretical investigations that could back up an informedpractical decisionism.

Bibliography

A more complete bibliography of Ayer’s work up to 1979 can befound in Macdonald 1979, in the Secondary Literature sectionbelow.

Primary Literature: Works by Ayer

• 1934a, “Demonstration of the Impossibility ofMetaphysics”,Mind, 43 (171): 335–345.
• 1934b, “The Genesis of Metaphysics”,Analysis, 1 (4): 55–58.
• 1936,Language, Truth, and Logic, London: Gollancz,2^nd Edition, 1946.
• 1940,The Foundations of Empirical Knowledge, London:Macmillan.
• 1948, “Correspondence”,The New Statesman andNation, July 10, 1948: 30–32.
• 1954,Philosophical Essays, London: Macmillan. (Essays onfreedom, phenomenalism, basic propositions, utilitarianism, otherminds, the past, ontology.)
• 1957, “The conception of probability as a logicalrelation”, in S. Korner, ed.,Observation and Interpretationin the Philosophy of Physics, New York, NY: DoverPublications.
• 1956,The Problem of Knowledge, London: Macmillan.
• 1962. “Philosophy and Science”,Soviet Studies inPhilosophy, 1 (1): 14–19.
• 1963,The Concept of a Person and other Essays, London:Macmillan. (Essays on truth, privacy and private languages, laws ofnature, the concept of a person, probability.)
• 1967, “Has Austin Refuted the Sense-Datum Theory?”Synthese, 18: 117–40. (Reprinted in Ayer 1969).
• 1968,The Origins of Pragmatism, London: Macmillan.
• 1969,Metaphysics and Common Sense, London: Macmillan.(Essays on knowledge, man as a subject for science, chance, philosophyand politics, existentialism, metaphysics, and a reply to Austin onsense-data theory.)
• 1969, “Philosophy and Politics”, inMetaphysicsand Common Sense, 240–246.
• 1971,Russell and Moore: The Analytical Heritage, London:Macmillan.
• 1972a,Probability and Evidence, London: Macmillan.
• 1972b,Bertrand Russell, London: Fontana.
• 1973,The Central Questions of Philosophy, London:Weidenfeld.
• 1979, “Replies”, in G. Macdonald, ed.,Perceptionand Identity, London: Macmillan, 277–333.
• 1980,Hume, Oxford: Oxford University Press
• 1982,Philosophy in the Twentieth Century, London:Weidenfeld.
• 1984,Freedom and Morality and Other Essays, Oxford:Clarendon Press.
• 1986,Ludwig Wittgenstein, London: Penguin.
• 1977,Part of My Life, London: Collins.
• 1984,More of My Life, London: Collins.
• 1992. “Reply to Paul Gochet”, in Hahn (1992),220–224.

Primary Literature: Works on Ayer

• Foster J., 1985,A. J. Ayer, London: Routledge.
• Gower, B. (ed.) 1987,Logical Positivism in Perspective:Essays on Language, Truth and Logic, London: Croom Helm.
• –––, 2006, “A. J. Ayer,Language,Truth and Logic”, in J. Shand (ed.),Central Works ofPhilosophy, Volume 4. The Twentieth Century: Moore to Popper,Chesham: Acumen, 195–213.
• Griffiths, A.P., 1991,A.J. Ayer Memorial Essays,Cambridge: Cambridge University Press.
• Hahn, L.E., 1992,The Philosophy of A.J. Ayer, OpenCourt.
• Hanfling, O., 1999,Ayer, London: Routledge.
• Harré, R. and Shosky, J. 1999, “Ayer’s View ofthe Vienna Circle: The Linacre Letter”,The Linacre Journal:A Review of Research in the Humanities, 3: 27–37.
• Honderich, T., 1991,Essays on A.J. Ayer, Cambridge:Cambridge University Press.
• Macdonald, G.F., 1979,Perception and Identity, London:Macmillan.
• Macdonald, Graham. and Wright, C., 1986,Fact, Science, andMorality: Essays on A. J. Ayer’s Language, Truth and Logic,Oxford: Blackwell.
• Martin, R., 2000,On Ayer, Belmont, CA: WadsworthPublishing Co.
• Rogers, Ben, 1999,A. J. Ayer: A Life, London: Chatto& Windus.
• Tuboly, A. T. (ed.) 2021a,The Historical and PhilosophicalSignificance of Ayer’s Language, Truth and Logic, Cham:Palgrave Macmillan.

Secondary Literature

• Altham, J., 1986, “The Legacy of Emotivism”, inMacdonald and Wright, 1986, 275–288.
• Ambrus, G. 2021, “The Evolution of Ayer’s Views on theMind-Body Problem”, in Tuboly (ed.) 2021a, 153–190.
• Austin, J.L., 1962,Sense and Sensibilia, Oxford:Clarendon Press.
• Berlin, I. 1973, “Austin and the Early Beginnings of OxfordPhilosophy”, in I. Berlin et al. (eds.),J. L. Austin,Oxford: Clarendon Press, 1–16.
• Blackburn, S., 1984,Spreading the Word, Oxford:Clarendon Press.
• –––, 1998,Ruling Passions, Oxford:Clarendon Press.
• Carnap, R. 1932/1959, “The Elimination of MetaphysicsThrough the Logical Analysis of Language”, in A. J. Ayer (ed.),Logical Positivism, Westport, Conn: Greenwood Press,60–81.
• Chalmers, D., 2004, “Epistemic Two-DimensionalSemantics” inPhilosophical Studies, 118 (1–2):153–226.
• Chapman, S. 2021, “‘Viennese Bombshells’:Reactions toLanguage, Truth and Logic from Ayer’sPhilosophical Contemporaries”, in Tuboly (ed.) 2021a,69–97.
• Church, A., 1949, “Review ofLanguage, Truth, andLogic”,Journal of Symbolic Logic, 14:52–3.
• Damböck, Ch. 2022, “The Politics of Carnap’sNon-Cognitivism and the Scientific World-Conception of Left-WingLogical Empiricism”,Perspectives on Science, 30 (4):493–524.
• –––, 2024, “Carnap and Heidegger.Political Antimetaphysics Versus Metaphysics as Metapolitics”,Geltung: Journal of Studies in the Origins of ContemporaryPhilosophy, 2 (2): 1–21.
• Dreier, James, 2004, “Meta-ethics and the problem ofCreeping Minimalism”, in Hawthorne 2004, 23–44.
• Frank, Ph. 2021,The Humanistic Background of Science, G.Reisch and A. T. Tuboly (eds.), Albany, NY: SUNY Press.
• Gettier, E.L., 1963, “Is Justified True BeliefKnowledge?” inAnalysis, 23 (6): 121–123.
• Gibbard, A., 1990,Wise Choices, Apt Feelings, Oxford:Clarendon Press.
• Glock, H-J. 2021, “Ayer’s Verificationism: Dead as aDodo?” in Tuboly (ed.) 2021a, 251–278.
• Hawthorne, John (ed.), 2004,Ethics (PhilosophicalPerspectives: Volume 18), Oxford, Malden, MA: Blackwell.
• Hempel, C. G. 1958, “The Theoretician’s Dilemma: AStudy in the Logic of Theory Construction”, in H. Feigl, M.Scriven and F. Maxwell (eds.),Concepts, Theories and theMind-Body Problem, Minneapolis: University of Minnesota Press,37–98.
• Jackson, F., 1998,From Metaphysics to Ethics, Oxford:Oxford University Press.
• Joad, C. E. M. 1948, “Logical Positivism, Fascism andValue”,The New Statesman and Nation, July 31, 1948:91–92.
• –––, 1950,A Critique of LogicalPositivism, London: Victor Gollancz.
• Juhos, B., 1969, “Logical and Empirical Probability”,Logique et Analyse, XII (47): 277–282.
• Kocsis, L. 2021, “Definition versus Criterion: Ayer on theProblem of Truth and Validation”, in Tuboly (ed.) 2021a,279–303.
• Koterski, A. 2023, “Did A. J. Ayer Bring Logical Positivismto England?Language, Truth and Logic and the ViennaCircle”,Grazer Philosophische Studien, 100 (3):253–276.
• Körner, S. 1979, “Ayer on Metaphysics”, inMacdonald, 1979, 262–276.
• Körner, S. 1991, “On the Relation between Common Sense,Science and Metaphysics”, in Griffiths, 1991, 89–103.
• Krishnan, N. 2023,A Terribly Serious Adventure, NewYork: Random House.
• Lewis, D.K., 1988, “Statements Partly AboutObservation”,Philosophical Papers, 17:1–31.
• Mace, C.A. 1934a, “Representation and Expression”,Analysis, 1 (3): 33–38.
• –––, 1934b, “Metaphysics and EmotiveLanguage”,Analysis, 2 (1/2): 6–10.
• Mackie, J.L., 1977,Ethics: Inventing Right and Wrong,Harmondsworth: Penguin.
• Mehta, Ved, 1965,Fly and the Fly-Bottle: Encounters withBritish Intellectuals, Baltimore: Penguin Books.
• Parker-Ryan, S. 2021, “Linguistic Analysis: Ayer and EarlyOrdinary Language Philosophy”, in Tuboly (ed.) 2021a,123–149.
• Pete, K. 2021, “Ayer and Berkeley on the Meaning of Ethicaland Religious Language”, in Tuboly (ed.) 2021a,307–331.
• Pincock, Ch. 2022, “Logical Empiricism in the AnglophoneWorld: Early Receptions”, in C. Limbeck-Lilienau and Th. Uebel(eds.),The Routledge Handbook of Logical Empiricism, NewYork and London: Routledge, 325–333.
• Quinton, A. 1991, “Ayer’s Place in the History ofAnalytic Philosophy”, in Griffiths, 1991, 31–48.
• Ramsey, F.P. 1927–29/1990, “The Nature ofTruth”, in N. Rescher and U. Majer (eds.),On Truth:Original Manuscript Materials (1927–1929) from the RamseyCollection at the University of Pittsburgh, Dordrecht: Kluwer,6–16.
• Rathgeb, N. 2021, “Ayer on Analyticity”, in Tuboly(ed.) 2021a, 101–121.
• Romilly, G. (=Oxonian), 1948, “A Visit to Oxford”,The New Statesman and Nation, June 26, 1948:518–519.
• Rowe, M. W. 2023,J.L. Austin: Philosopher and D-DayIntelligence Officer, Oxford: Oxford University Press.
• Russell, B. 1910, “On the Nature of Truth andFalsehood”, inPhilosophical Essays, London: Longmans,Green, and Co., 170–185.
• Ryle, G., 1970, “Autobiographical”, in O. P. Wood andG. Pitcher (eds.),Ryle, London: Macmillan, 1–15.
• –––, 1976, “Fifty Years of Philosophy andPhilosophers”,Philosophy, 51 (198): 381–389.
• –––, 1999. “The Genesis of ‘Oxford’Philosophy”,Linacra Journal, 3: 109–114.
• Schroeder, M., 2010,Noncognitivism in Ethics, London:Routledge.
• Smith, M., 1986, “Should We Believe in Emotivism”, inMacdonald and Wright, 1986, 289–310.
• Stevenson, C.L., 1944,Ethics and Language, New Haven,Conn.: Yale University Press.
• Thau, M., 2004, “What is Disjunctivism?” inPhilosophical Studies, 120: 193–253.
• Tuboly, A.T. 2020, “A Cricket Game, A Train Ticket and aVacuum to be Filled: Ayer’s Logical Positivism as a Focal Pointfor Post-War British Cultural Struggles”,British Journalfor the History of Philosophy, 28 (6): 1134–1150.
• –––, 2021b, “Introduction: From Spying toCanonizing – Ayer and HisLanguage, Truth andLogic”, in Tuboly (ed.) 2021a, 1–37.
• Uebel, Th. 2007,Empiricism at the Crossroads: The ViennaCircle’s Protocol-Sentence Debate, Chicago: OpenCourt.
• –––, 2018, “Carnap’s Transformationof Epistemology and the Development of His Metaphilosophy”,The Monist, 101 (4): 367–387.
• –––, 2021. “A Logical Positivist’sProgress: A Puzzle about Other Minds in Earl Ayer Resolved”, inTuboly (ed.) 2021a, 191–247.
• Vrahimis, A. 2021, “Language, Truth and Logic andthe Anglophone Reception of the Vienna Circle”, in Tuboly (ed.)2021a, 41–68.
• Wilks, C., 2002,Emotion, Truth and Meaning, KluwerAcademic Publishers: Dordrecht.
• Williams, B., 1979, “Another Time, Another Place, AnotherPerson”, in Macdonald (ed.) 1979, pp. 252–261.
• Wright, C., 1986, “Scientific Realism, Observation, and theVerification Principle”, in Macdonald and Wright, 1986,247–274.
• –––, 1989, “The Verification Principle:Another Puncture – Another Patch”,Mind, 98:611–22.

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