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In Language, Truth, and Logic, Sir A. J. Ayer presents a modified version of logical positivism that he prefers to call “logical empiricism.” However, the doctrines, particularly their implications for philosophy, are largely those of logical positivism, and the work serves to bring these together succinctly and vigorously. Therefore, the book has had great importance as a positivistic document and as a center of controversy about positivistic tenets. In it, Ayer offers to solve the problems of reality, perception, induction, knowledge, meaning, truth, value, and other minds. He presents no great new idea; rather, he has modified and brought into logical consistency solutions proposed by others. In the introduction to the 1946 second edition, Ayer provided further explication and modified a few beliefs, but essentially his position remained unchanged.
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Ayer attacks metaphysics, saying that he will deduce the fruitlessness of attempting knowledge that transcends the limits of experience from the “rule which determines the literal significance of language.” The sentences of metaphysics, failing to meet this rule, are meaningless.
Ayer finds the criterion of meaning in the verification principle. “We say that a sentence is factually significant to any given person, if, and only if, he knows how to verify the proposition which it purports to express—that is, if he knows what observations would lead him, under certain conditions, to accept the proposition as being true, or reject it as being false.” Another possible kind of meaningful sentence is the tautology. However, any sentence that is neither a tautology nor a verifiable proposition (by this criterion) is a mere pseudoproposition, a meaningless sentence.
Certain provisions qualify this tenet. Ayer distinguished practical verifiability and verifiability in principle. Some sentences are not practically verifiable because of inconvenience or the present state of science and culture. If one knows what observations would decide such a matter if one were in a position to make them, the proposition is verifiable in principle. A further distinction is that between “strong” verifiability and “weak” verifiability. According to the “strong” theory, advanced by the Vienna Circle of logical positivists, a sentence is meaningful only if it is conclusively verifiable empirically; according to the “weak” theory, it is meaningful if experience may render it probable. Ayer chooses the “weak” theory on the basis that because no empirical demonstration is ever 100 percent conclusive, the “strong” theory leaves no empirical statement meaningful. By using the “weak” theory, Ayer believes he allows general propositions of science and propositions about the past, which previous positivistic writers found problematic, to have meaning. The proposed principle rules out such assertions as the statement that the world of sense is unreal and such questions as whether reality is one substance or many. No experience could decide these issues, so they have no literal significance. Metaphysicians have usually been misled by the grammar of language so that they posit an entity (“substance,” “Being”) where grammar requires a noun as the subject of a sentence, even though thought may exert no such requirement.
By the abandonment of metaphysics, the philosopher is freed from the function of constructing a deductive system of the universe from first principles, for first principles cannot come from experience, whose propositions are only hypotheses and never certain. However, if they are taken a priori, they are only tautologies, which cannot apply to the universe as factual knowledge.
The problem of induction can be set aside as unreal. It is the attempt to prove that certain empirical generalizations derived from past experience will hold good also in the future. It must have either an a priori or an empirical solution. However, in the first case, it is improper to apply tautologies to experience, for they cannot apply to matters of fact; and in the second, one simply assumes what one set out to prove. Because Ayer can conceive no test that would solve the “problem” through experience, he concludes that it is not a genuine problem. In actuality, people place their faith in such scientific generalizations as enable them to predict future experience and thus control the environment; there is no general logical problem about this practice.
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A common mistake is to assert that without a satisfactory analysis of perception, one is not entitled to believe in the existence of material things. Rather, the right to believe in their existence comes simply from the fact that one has certain sensations, for to say the thing exists is equivalent to saying the sensations are obtainable. The business of philosophers is to give a correct definition of material things in terms of sensations. They are not concerned with the properties of things in the world but only with how people speak of them. The propositions of philosophy are not factual, but linguistic in character: “They do not describe the behavior of physical, or even mental, objects; they express definitions, or the formal consequences of definitions.” Philosophy is a department of logic. It is independent of any empirical, not to say metaphysical, assumptions. Often propositions that are really linguistic are so expressed as to appear to be factual. “A material thing cannot be in two places at once” is actually linguistic, recording “the fact that, as the result of certain verbal conventions, the proposition that two sense-contents occur in the same visual or tactual sense-field is incompatible with the proposition that they belong to the same material thing.” The question “What is the nature of X?” asks for a definition, which is always a linguistic statement.
Philosophical analysis essentially provides definitions. However, such definitions are not the most frequently occurring kind, that is, explicit, or synonymous, definitions giving an alternative symbol or symbolic expression for the term to be defined. Rather, they are definitions in use, which are made by showing how a sentence in which the definiendum (expression that is being defined) occurs can be translated into equivalent sentences that do not contain the definiendum or any of its synonyms. An example taken from English philosopher Bertrand Russell defines “author” in the sentence, “The author of Waverley was [Sir Walter] Scott,” by providing the equivalent, “One person, and one person only, wrote Waverley, and that person was [Sir Walter] Scott.” Such definitions clarify sentences where no synonym for the definiendum exists and where available synonyms are unclear in the same fashion as the symbol needing clarification. A complete philosophical clarification of a language would first enumerate the types of sentences significant in that language, then display the relations of equivalence that hold between sentences of various types. Such a set of definitions would reveal the structure of the language examined, and any truly philosophical theory would hence apply to a given language.
Some symbols denote simple sense-contents and others logical constructions, the latter making it possible to state complicated propositions about the elements of the logical constructions in a relatively simple form. However, logical constructions are not inherently fictions. Rather, material things are among such logical constructions. The definition in use will restate the definiendum, naming a material thing by translating it into symbols that refer to sense-contents that are elements of the material thing. In other words, roughly, to say something about a table is always to say something about sense-contents. The problem of the “reduction” of material things into sense-contents, long a chief part of the problem of perception, is a linguistic problem readily solved by providing definitions in use. To accomplish this reduction, Ayer stipulates that two sense-contents resemble each other directly when there is either no difference, or only an infinitesimal difference, between them and indirectly when they are linked by a series of direct resemblances amounting to an appreciable difference. He stipulates further that two sense-contents are directly continuous when within successive sense-fields there is no difference, or only an infinitesimal difference, between them, with respect to the position of each in its own sense-field and indirectly continuous when related by an actual, or possible, series of direct continuities. Any two of one’s sense-contents, then, are elements of the same material thing when they are related to each other by direct or indirect resemblance and by direct or indirect continuity.
Ayer assumes that the object of a theory of truth is to show how propositions are validated. Like all questions of similar pattern, the question “What is truth?” calls for a definition. Consequently, no factual theory is needed to answer it. The real question discussed most of the time in “theories of truth” is “What makes a proposition true or false?”
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Ayer adopts the distinction between analytic and synthetic propositions. Each has its own validation. “A proposition is analytic when its validity depends solely on the definitions of the symbols it contains, and synthetic when its validity is determined by the facts of experience.” While “Either some ants are parasitic or none are,” an analytic proposition, is undubitably and necessarily true, it provides no actual information about ants. As a tautology, it has no factual content and serves only to help us understand matters of language. The valid propositions of logic are true by tautology and are useful and surprising in revealing hidden implications in our sentences. They can help us gain empirical knowledge, but it is not the tautologies that render empirical knowledge valid. Whether a geometry actually can be applied to physical space is an empirical question that falls outside the scope of the geometry itself. There is therefore no paradox about the applicability of the analytic propositions of logic and mathematics to the world.
Synthetic propositions, Ayer affirms, are validated by experience. Experience is given in the form of sensations. Sensations are neither true nor false; they simply occur. Propositions about them are not logically determined by them in one way or another; hence, while these are perhaps largely dependable, they may be doubted. Similarly, they may be confirmed by additional experience. In other words, “Empirical propositions are one and all hypotheses.” In fact, whenever a verification is carried out, it is applied to an entire system of hypotheses—a principal one, together with supplementary hypotheses that often are adjusted by the verification rather than by the principal hypothesis. Therefore, the “facts of experience” can never per se oblige one to abandon a particular hypothesis because one may ever continue without contradiction to explain invalidating instances in various ways while retaining the principal hypothesis. One must, of course, retain a willingness to abandon it under certain circumstances because of experience, or else one makes of it not a hypothesis but a definition. It must be granted that one is not always rational in arriving at belief—that is, one does not always employ a self-consistent accredited procedure in the formation of one’s beliefs. That a hypothesis increases in probability is equivalent to saying that observation increases the degree of confidence with which it is rational to entertain the hypothesis.
The exposition of synthetic propositions, every one of which is a rule for the anticipation of future experience, constitutes Ayer’s validation of the verification principle, for it comes to just what the verification principle states, that the literal significance of an empirical proposition is the anticipated sense-contents entailed in it.
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To account consistently for statements of value with empirical principles, Ayer holds that descriptive ethical sentences are empirical statements and that normative ethical sentences are “absolute” or “intrinsic,” not empirically calculable, and indefinable in factual terms. The normative symbols in a sentence name no concepts, add nothing to the factual content. Thus, normative sentences are not capable of being true or false. They simply express certain feelings of the speaker. They are not even assertions that the speaker has a certain feeling, for such assertions would be empirical and subject to doubt. Thus the question of their having any validity at all is removed.
How, then, can one dispute about value? Ayer maintains that actually one never disputes about questions of value but only about questions of fact. The pattern usual in such a dispute is to exhibit to one’s opponent what one believes to be the facts, assuming a common framework of value statements, and attempting to bring the opponent to one’s way of seeing the facts.
As to religious knowledge, one cannot appeal to tautologies for factual truth about God, for these are mere stipulations of one’s own. Nor can one have empirical propositions about God, for one can conceive of no experience that would bring one different sense-contents if God exists than if he does not. Hence, the notion is metaphysical and meaningless.
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Ayer applies a complete phenomenalism to the traditional problems of the self and knowledge of the world. He denies that the given needs a logical rather than sensory justification. Further, he rejects the pattern of subject-act-object as an account of perception. He defines a sense-content not as the object but as a part of sense-experience, so that the existence of a sense-content always entails the existence of a sense-experience. Hence, the question of whether sense-contents are mental or physical is inapplicable. Such a distinction can apply only to the logical constructions that are derived from them. The difference between mental and physical objects lies in differences between the sense-contents, or in the different relations of sense-contents that constitute objects.
The self may be explained in similar terms. “It is, in fact, a logical construction out of the sense-experiences which constitute the actual and possible sense-history of a self.” To ask its nature is to ask what relationship obtains between sense-experiences for them to belong to the sense-history of the same self. Rather than retain the metaphysical notion of a substantive ego, one can identify personal identity simply in terms of bodily identity, and that in turn is to be defined in terms of the resemblance and continuity of sense-contents. To say anything about the self is always to say something about sense-contents. One knows other selves empirically, just as one knows physical things and one’s own self empirically.
Ayer urges the unity of philosophy with the sciences. Rather than actually validating scientific theory, the philosopher’s function is to elucidate the symbols occurring in it. It is essential to the task that the philosopher understand science. Philosophy must develop into the logic of science.
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As well as providing further exposition, Ayer’s introduction to the second edition contains some modifications of doctrine that deserve notice. In the interim between editions, he came to accept a belief of the logical positivists that he opposed in the first edition, that some empirical statements may be considered conclusively verified. These are “basic statements,” referring to the sense-content of a single experience, and their conclusive verification is the immediate occurrence of the experience to which they refer. As long as these merely record what is experienced and say nothing else, they cannot be factually mistaken, for they make no claim that any further fact could confute. However, this change makes little difference to the chief doctrine, Ayer maintains, for the vast majority of propositions are not of this sort.
Ayer introduces the term “observation-statement,” to designate any statement “which records an actual or possible observation.” To remove the objection that, as originally stated, the principle allows any indicative statement whatever to have significance, Ayer amends its expression to say that the principle of verification requires of a literally meaningful, nonanalytic statement that it should be either directly or indirectly verifiable. For it to be directly verifiable, it must be an observation-statement, or it must entail at least one other observation-statement not entailed by the other observation statements alone. To be indirectly verifiable, first, in conjunction with certain other premises, a statement must entail one or more directly verifiable statements not deducible from the other premises alone and, second, the other premises must include no statement that is not either analytic, or directly verifiable, or indirectly verifiable independently.
Ayer gives up the position that a priori propositions are linguistic rules, for they can properly be said to be both true and necessary, while linguistic rules cannot be called true and are arbitrary. Descriptive linguistic statements of contingent empirical fact of language usage are, however, the basis for statements of logical relationships—which are necessary truths. Ayer admits doubts as to whether his account of the experiences of others is correct, yet says, “I am not convinced that it is not.” He confesses error in assuming that philosophical analysis consists mainly in providing “definitions in use.” Such a result is the exception rather than the rule; and in fact, for statements about material things, such definition becomes impossible because “no finite set of observation-statements is ever equivalent to a statement about a material thing.”
Finally, rather than classify philosophical statements alongside scientific statements, Ayer states that “it is incorrect to say that there are no philosophical propositions. For, whether they are true or false, the propositions that are expressed in such a book as this do fall into a special category . . . asserted or denied by philosophers.” Lexicographers are concerned with the use of particular expressions; however philosophers are concerned with classes of expressions; and their statements, if true, are usually analytic.
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Austin, J. L. Sense and Sensibilia. New York: Oxford University Press, 1962. A widely read response from an ordinary language perspective to A. J. Ayer’s early epistemological formulations. Austin dismissed Ayer’s views as “weak” and “full of jokes.”
Foster, John. The Philosophical Arguments of Philosophers: Ayer. London: Routledge and Kegan Paul, 1985. A systematic and detailed presentation of Ayer’s philosophical views as contained in his major works. A high-level work, but probably the most authoritative secondary source on Ayer’s views.
Griffiths, A. Phillips. A. J. Ayer Memorial Essays. Cambridge, England: Cambridge University, 1991. An excellent collection of commentaries on Ayer’s contributions to philosophy by those who knew him personally. Includes a British Broadcasting Corporation interview with Ayer conducted during the last year of his life.
Hahan, Lewis, E., ed. The Philosophy of A. J. Ayer. Library of Living Philosophers series. La Salle, Ill.: Open Court, 1992. Ayer responds to twenty-one of the twenty-four papers addressing his work. Also contains Ayer’s essay “My Mental Development” and a bibliography of his publications. The best survey of his life’s work.
Hanfling, Oswald. A. J. Ayer. New York: Routledge, 1999. An excellent biographical introduction to the thoughts of the philosopher, clearly presented and requiring no special background. Bibliography.
Hanfling, Oswald. A. J. Ayer: Analysing What We Mean. London: Phoenix, 1997. An examination of Ayer’s work and his contribution to philosophy.
MacDonald, G. F., ed. Perception and Identity: Essays Presented to A. J. Ayer with His Replies to Them. London: Macmillan, 1979. A set of essays honoring Ayer upon his retirement from Oxford, made more useful by the inclusion of his responses to each paper.
Magee, Bryan. Modern British Philosophy. New York: St. Martin’s Press, 1971. Interviews with leading British philosophers including A. J. Ayer and his early mentor Gilbert Ryle. A sound and easily understood presentation of Ayer’s views.
Priest, Stephen. The British Empiricists: Hobbes to Ayer. New York: Penguin Books, 1990. An excellent source for placing Ayer’s work in the tradition from which it emerged.