AJ. Ayer was born in London on 29 October 1910 and died there on 27 June 1989. He was educated as a scholarship student in classics at Eton College and Christ Church, Oxford, graduating in Greats in 1932. He was a lecturer (1932–35) and research student (1935–40) at Christ Church, Oxford. From 1940 to 1945 he served in Military Intelligence with the Welsh Guards, rising to the rank of captain. After the war he was fellow and Dean of Wadham College, Oxford (1945–6), and then Grote Professor of the Philosophy of Mind and Logic at the University of London (1946–59), where he did much to create a strong postgraduate programme. Ayer returned to Oxford as Wykeham Professor of Logic (1959–78), but took leave for such distinguished visiting posts as William James Lecturer at Harvard (1970), John Dewey Lecturer at Columbia (1971) and Gifford Lecturer at Aberdeen (1972–3). He was knighted in 1970.
Over his lifetime, Ayer was a prolific author of books and notable essays, primarily in epistemology and philosophy of mind, and, to a lesser extent, philosophical logic and metaphysics. His work was translated into many languages, and many of his essays were republished in collections of his own essays, as well as in numerous other anthologies, a sign of their philosophical insight, influence, literary merit and accessibility. Nonetheless, his best-known work remained his first book.
At Oxford he attended lectures by H.H. Price and was tutored by Gilbert Ryle , falling under the intellectual influence of Russell and Wittgenstein . At Ryle’s urging, he took leave to attend the Vienna Circle from 1932 to 1933 to learn about logical positivism. In Vienna, he also met the young American philosopher, W.V. Quine. On returning to England he was urged to publish what he had learned and produced Language, Truth, and Logic (1936), a short, lively book that became one of the most widely read philosophical works in the twentieth century. It synthesized the views of the positivists, Schlick, Neurath and Carnap, with some arguments of his own. The result may not have been entirely original, but it was never boring and managed to say something provocative about most of the major topics in philosophy.
At the core of his position was the verification criterion of meaningfulness, according to which empirical observations must be relevant to the determination of the truth or falsity of any statement that was factually significant. The only other literally significant truths were those that were analytically and necessarily true. Natural science consisted of factually significant statements. Logic and mathematics, Ayer argued, consisted of analytically true statements. These, Ayer variously claimed, were tautologies that were true by virtue of the rules or conventions of language, that we could not deny without contradicting ourselves, that expressed our determination to use words in certain ways rather than any facts about the world, and that were knowable a priori by reflecting on the meanings of the terms used in making them. Later, critics pointed out that these various characterizations of necessary truth were hardly equivalent, and Quine argued that the distinctions between sentences that depended on them were not very hard and fast.
To the extent that philosophers confined themselves to the analysis of literally significant statements or to showing their logical relations or criticizing attempts to do so, the statements they made were literally significant and the legitimate task of philosophy. To the extent that philosophers purported to make experience-transcendent claims about reality, their claims were metaphysical pseudo-statements without literal significance. Traditional metaphysicians had been misled by the superficial grammatical similarity of their claims, for example ‘there are universals’, to factual claims, for example ‘there are geese’, into thinking that metaphysical claims also were of factual significance. Ayer argued that many of the traditional disputes of philosophy, for example realism vs idealism, monadology vs monism, turned out to be, to the extent that they could not be reconfigured as disputes about the analysis of statements in use or shown to be empirical issues, simply pseudo-problems. Most theological statements were similarly dismissed. Indeed, for Ayer, the positions of the atheist, the agnostic and the theist alike were without literal significance. However, questions about the existence and nature of material objects, the self and other minds were reconstrued as ones about the translation of sentences about them into sentences about the contents of sense experience. Throughout the rest of his career, Ayer struggled with issues about how to understand such sentences in empirical terms, often switching his views. Ethical and aesthetic statements, on the other hand, could not be translated into statements about our actual and possible experience, but were simply the expression of our attitudes to classes of actions and objects. This was a view he never really abandoned.
Following Frank Ramsey , Ayer argued that ‘true’ did not pick out a real property of statements. He concluded that the philosophical problem of the nature of truth, for example correspondence or coherence, was also a pseudo-problem, and that the only real question was under what conditions statements were verified. A priori verifiable statements could be certain, but empirically verifiable ones could be at best probable. The latter divided into two categories: observation reports recording sense experience, and empirical hypotheses that allowed us to anticipate and predict sense experience. The former were not certain because even the most basic empirical concepts like red were not purely ostensive or demonstrative but classified experiences as belonging to a set of resembling experiences and so went beyond what was immediately given in experience. Empirical hypotheses, on the other hand, were always subject to further test and thus also could never be exhaustively confirmed. The problem of induction, construed as the problem of finding a non-circular reason for thinking inductive inferences had mostly true conclusions, was dismissed as a pseudo-problem. However, in a novel twist, the rationality of induction was trivially guaranteed since ‘rationality’ by definition was simply a matter of employing a self-consistent accredited procedure in the formation of all one’s beliefs.
Ayer also argued that empirical hypotheses were not conclusively falsifiable since individual hypotheses had observational implications only in conjunction with a host of background assumptions that might be abandoned instead when a prediction failed. Ayer recognized the holistic implication: what is tested by experience is strictly a system of hypotheses. However, unlike Quine, he failed to recognize the full force of this point until much later: only systems of hypotheses have empirical significance, and thus there is no legitimate philosophical project of analysing types of individual statements about material objects, the self, other minds, the past, theoretical entities in science, etc. to find their empirical content. Indeed, it caused problems for the verifiability criterion of meaningfulness itself. As critics pointed out, on the one hand, individual empirical hypotheses were not empirically testable all by themselves, but, on the other hand, metaphysical or theological propositions might be part of systems of hypotheses that were as a whole empirically significant. Ayer struggled to find a defensible form of the verifiability criterion of meaningfulness. In addition, critics wondered whether the verifiability criterion itself was analytic or empirically verifiable. Ayer’s response that it was a stipulative definition of ‘meaningful’ seemed to allow his opponents simply to reject the stipulation.
Ayer’s second book, The Foundations of Empirical Knowledge (1940), focused more narrowly on epistemology. In opposition to Price and others, Ayer argued that the idea that in sense perception we were not immediately presented with material objects but rather sense-data was not some fact about perception that we discovered on reflection, or a consequence of the argument from illusion. Instead it was a way of talking about perception that was useful to adopt to characterize the relation between empirical theory and empirical evidence, between uncertain empirical hypotheses the content of which goes beyond the evidence for them and observation reports the content of which does not go beyond our evidence for them. Allowing for error with respect to sense-datum reports would thus defeat their purpose. Likewise, the privacy of sense experience was regarded as a linguistic truth rather than a discovery about sense experience. Ayer thus abandoned his earlier fallibilistic holism for a more traditional foundationalism, albeit for somewhat non-traditional reasons. However, he maintained his overall phenomenalistic analysis of material object statements as referring to nothing over and above possibilities of sense-data, and provided a detailed phenomenological analysis of the experiential basis of our conception of material things as existing independently of our experience. Sense-data theory in various guises later fell into disrepute in Britain, thanks largely to Wittgenstein’s Philosophical Investigations (1953) and J.L. Austin’s Sense and Sensibilia (1962). Ayer patiently replied to each respectively in ‘Can There Be a Private Language’ and ‘Has Austin Refuted the Sense-Datum Theory?’, both reprinted in Metaphysics and Common Sense (1969)
Ayer’s third book, The Problem of Knowledge (1956), which he thought his best, shed much of the trappings of positivism and was very influential in subsequent epistemological thinking in Britain and America. Ayer outlined the now standard tripartite analysis of prepositional knowledge as a matter of being sure of something that was true and that one had the right to be sure of. However, he now argued that one could make genuine, nonverbal, mistakes even in claims about the character of one’s own immediate experience. Yet, that did not impugn one’s right to be sure of the truth of these claims without further evidence or reasons for their truth. Moreover, although there could not be a non-circular justification of inductive inference, our reliance on it was not irrational since there cannot – at least on pain of begging the question – be a higher standard of rationality that it failed to meet. Other standard epistemological problems, such as the external world, other minds, scientific entities or the past, could be represented, Ayer argued, as having four steps. First, our knowledge of these is not direct. Second, there is no justifying deductive inference for them from premises we had the right to be sure of. Third, there is no inductive inference for them, and fourth, as a sceptical conclusion, our belief in them could not be justified at all. Intuitionists or naive realists deny the first, reductionists the second, and the scientific approach the third. What Ayer called the method of descriptive analysis denied the underlying assumption that inferential justification had to be either inductive or deductive. On this approach, the task of epistemology was simply to articulate the relationship between theory and evidence in practice, not to justify it by appeal to further standards the defence of which could only be as questionbegging as their denial. That might, in some cases, depending on the outcome of the descriptive analysis, lead to the claim that a kind of knowledge was direct, or reducible to another, or inductively derivable, but need not.
Ayer himself embraced descriptive analysis, thinking that its response to scepticism made it the heir of the other responses. He rejected the reductivism that had previously led him to embrace phenomenalism about the external world, behaviourism about other minds, and the construal of statements about the past as about present and future verifying observations. Ayer argued that in particular cases memory beliefs were justified without inference from other knowledge, but corrigibly and fallibly so. However, he argued that our beliefs about other minds were in particular cases justified to some degree by inductive or analogical reasoning, although reflection on particular cases and the limitations of our evidence revealed that our degree of rightful confidence was often less than we might uncritically think it to be. Statements about physical objects, on the other hand, were a theoretical interpretation of our sense experiences that had no meaning apart from their relation to sense experience but were irreducible to statements about the sense experiences. It is characteristic of what is meant by ‘there is a table before me’ that statements about apparent table experiences or sense-data constitute corrigible and fallible evidence for it. The new focus on the careful description of the criteria of knowledge in various domains that characterizes much recent epistemology is partly responsible for its flourishing state.
Ayer returned to a broader consideration of the nature of philosophy and its many issues in The Central Questions of Philosophy (1973), based on his Gifford Lectures and drawing on a wide variety of essays and lectures. Rejecting the verification criterion of meaningfulness, Ayer now argued that metaphysical theories were literally significant only if they had some explanatory value, helping at least indirectly to account for observable facts. This he granted was a stipulation, but vindicated pragmatically because otherwise it would be a mystery why anyone would care whether the theory was true. Ayer was sympathetic to the commonsensism he saw as underlying the work of Moore, Wittgenstein and Ryle, but thought the sort of conceptual analysis they engaged in could only be a starting-point for philosophy since common usage is not fixed but changes as our ways of interpreting experience gradually change. The need for radical reform of our existing conceptual practices thus cannot be ruled out. With respect to our perceptual knowledge of material objects, Ayer defended a version of the ‘scientific approach’ according to which material objects were posited as part of a theory justified by its ability to explain contingent features of our experience. Belief in other minds was likewise part of an explanatory theory, and the degree to which we were right to hold it less weak than it might be, had its basis been purely analogical. Ayer dealt similarly with our belief in the reality of the past. The very general beliefs about our relationship to the world and others that our explanatory theories presuppose are justified by the explanatory success of these theories. However, the appeal to explanatory coherence underlying the ‘scientific approach’ was not irrational just because it failed the sceptic’s standards.
Ayer granted that we could ask why we should assume explanatory success so far gave us a reason for thinking that a theory would continue to work. That was to raise Hume’s problem of induction. Ayer granted Hume that events in the world were logically distinct. Although many of the ways we describe events are not atomistic, for example ‘soluble’ or ‘sibling’, Ayer thought there was nonetheless a regimented theory of the basic facts of the world which was atomistic and which he called the ‘primary system’, as opposed to our full explanatory theory of the world which he called the ‘secondary system’. (Both systems, he thought, could be literally true.) He also granted Hume that there was no real relation of natural necessity holding between events. Natural necessity was simply what is excluded by natural law. Natural laws were simply true generalizations we were willing to project over unknown or imaginary cases. Ayer argued that there were epistemic probabilities or statements of credibility that were irreducible to logical probabilities or frequencies. In justifying our acceptance of generalizations, we ultimately assume that acceptance of a generalization in the face of favourable evidence of such and such strength is provisionally justified, just as we assume that confident judgements of perception and memory are prima facie justified. The further assurance the Humean sceptic demands is unavailable but also unnecessary. Finally, as various paradoxes of induction showed, there was latitude in which hypotheses we projected from the evidence and those which we saw as more likely to be right reflected, as always, the theories we already accepted.
However, Ayer refused to abandon the idea that there were truths that were logically necessary and analytic. He granted Quine that logical and mathematical truths confront the empirical facts as part of our overall belief system, but argued that, though empirical facts could show some of them to be unserviceable, for example in quantum mechanics or relativity theory, empirical facts could not invalidate them. Ayer was willing to allow that there were distinctive religious or mystical experiences, but thought their best explanation physiological or psychological. However, even if such explanations turned out to be insufficient, but required the postulation of a distinctive objective cause, we should only have reason for thinking it a novel kind of object or feature in the world rather than a transcendent one like God. Nor did he think there any empirical reason for thinking that the world or life as a whole had any meaning or purpose. Ayer remained an empiricist throughout the changes in his views over his life.
Later in his career, he wrote several works on the history of philosophy. He was more concerned with critically engaging authors in issues close to his own heart so as to advance our appreciation of the issues and the philosophical merits and demerits of their views than with placing authors in historical context. The most substantial of such works was The Origins of Pragmatism (1968) and Russell and Moore: The Analytical Heritage (1972). Although he wrote little on ethics or political philosophy, Ayer was a public philosopher. He made frequent appearances on the BBC. He chaired the Society for Homosexual Law Reform, helping to change public opinion to decriminalize homosexual activity between consenting adults. In the 1960s, he also served on a Commission on Public Education in the British Isles that led, among other things, to the elimination of corporal punishment, and was knighted for his services. Finally, late in life, Ayer published his autobiography in two popular volumes.