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Last Updated on May 5, 2015, by eNotes Editorial. Word Count: 1305

A. J. Ayer’s Language, Truth, and Logic was the first systematic presentation in English of the doctrines of logical positivism. While a student at Oxford University, Ayer spent the academic year 1932-1933 in Vienna attending the lectures and meetings of a group of philosophers, mathematicians, and scientists who called themselves...

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A. J. Ayer’s Language, Truth, and Logic was the first systematic presentation in English of the doctrines of logical positivism. While a student at Oxford University, Ayer spent the academic year 1932-1933 in Vienna attending the lectures and meetings of a group of philosophers, mathematicians, and scientists who called themselves the Vienna Circle. He quickly absorbed the basic tenets of the Vienna Circle and wrote Language, Truth, and Logic shortly after his return to England.

Ayer accepts the traditional empiricist view of philosophers such as David Hume that all genuine propositions either are analytic (in the sense, for Ayer, of being true solely by virtue of linguistic rules) or are empirically verifiable. Since analytic propositions are true in virtue of the meanings of the words composing them, they cannot be used to make factual assertions about the world. The tautological proposition “Either it is raining or it is not” is analytic in this sense, and it therefore says nothing about actual weather conditions. Because analytic propositions are true by virtue of meaning alone, Ayer believes, they can be known independently of experience; that is, they are knowable a priori.

In addition to tautologies and conceptual truths (for example, “Red is a color”), according to Ayer, the set of analytic propositions includes the necessarily true propositions of logic and mathematics. Traditional empiricists and Ayer maintain that propositions that are not analytic, and so are not true solely by virtue of linguistic rules, cannot be known a priori; they cannot be known by pure reason alone. It requires perceptual experience or some sort of empirical investigation to determine whether such propositions are true or false. Because these propositions are not true solely in virtue of linguistic rules, they have factual content and thus can be used to make informative assertions about the way things are in world.

Traditional empiricism was thus primarily a claim about knowledge and justification: The only propositions that can be known without empirical investigation are ones that are true by definition (for Ayer and other logical positivists, by virtue of linguistic rules), so any informative proposition can be known only on the basis of perceptual experience. In other words, the empiricists denied the rationalist claim that a priori knowledge of the world is possible.

With the principle of verification, Ayer and the logical positivists take empiricism to the semantic level by focusing on meaning rather than knowledge. This principle says that, in order to be meaningful, a proposition that is not analytic must be empirically verifiable. It must be possible, that is, to specify what sort of perceptual experiences would demonstrate that the principle is true or false. Propositions that do not satisfy this criterion of meaningfulness are declared by Ayer and the logical positivists to be meaningless and devoid of cognitive significance. Ayer’s version of verificationism does not require that the proposition be conclusively verifiable. His version more modestly requires only that there be possible sensory experiences that are relevant to the question of whether a statement is true or false. Furthermore, in Ayer’s version of the principle of verification, it is not necessary for verification to be practically possible; it is enough that verification could be carried out in principle.

With the principle of verification in place, Ayer goes on to argue that much of traditional metaphysical philosophy is not merely false but also meaningless nonsense. Metaphysics, as traditionally conceived, attempts to determine the nature of the world in itself, the reality “behind” the phenomenal world given in perceptual experience. The metaphysician, using pure a priori reasoning, claims to penetrate the veil of appearance and to arrive at the truth regarding the ultimate nature of reality. Ayer argues that metaphysical assertions, which are intended to be genuine assertions about the way the world is in itself, cannot be cognitively significant since they purport to describe that which cannot be an object of human experience. For example, theological claims such as “God exists” are regarded by Ayer as not merely false but also meaningless nonsense since there is no empirical evidence that could either confirm or refute that claim. The controversy between realists and idealists about the existence and nature of the external world, to take another example, is judged by Ayer to be a meaningless debate since no possible empirical evidence could decide the issue one way or the other. Realists maintain that there is a mind-independent physical world that causes perceptual experiences, while idealists assert that the world consists of minds and their ideas. Ayer points out that this whole controversy is meaningless since, he asserts, the evidence derived from the senses could never decide which of these two theories is correct.

The principle of verification guides Ayer regarding the proper task of philosophy. For Ayer, the role of philosophy is to use logic to clarify and analyze the concepts and propositions of science and common sense. Rather than engaging the fruitless debate between realists and idealists about the external world, Ayer suggests that philosophers look at the meaning of commonsense assertions about the external world in the light of the principle of verification.

According to Ayer, statements about physical objects are equivalent to statements about actual and possible experiences. To say, for example, that there is a chair in the next room means that, if someone were to go into the room, that person would have perceptual experiences of a chair. This view, which Ayer calls phenomenalism, is not intended to be a metaphysical theory about the ultimate nature of reality: He is not asserting that reality is essentially composed of minds and experiences. Such a theory would be just more meaningless metaphysics. Ayer’s phenomenalism is, rather, a theory about the meaning of statements about physical objects. His analysis is intended to capture the empirically verifiable content of statements about physical objects. Philosophy as conceived by Ayer is not, then, a body of knowledge. It is, rather, the activity of analyzing and clarifying the propositions of science and everyday life.

One of the more notorious doctrines of Language, Truth, and Logic is Ayer’s emotivist analysis of ethical propositions. Ayer believes that ethical assertions, such as “Stealing is wrong,” are not analytic in the sense of being true by virtue of meaning alone. They are also not empirically verifiable: No perceptual experience could verify that stealing is wrong. Thus, Ayer’s verificationism would seem to imply that ethical assertions should be regarded as meaningless nonsense. Given the importance of such statements in human life, this implication of the principle of verification seems to present a serious objection to that principle. Ayer deals with this problem by developing an emotivist theory of meaning. This theory says that ethical claims should not be interpreted as having factual or cognitive significance but rather as having emotive significance. They are not genuine assertions that are either true or false. Instead, they are exclamations that express a speaker’s emotions and attitudes toward actions and persons. To say, then, that stealing is wrong is to express one’s disapproval of stealing.

In 1946, Ayer wrote an extensive introduction for the second edition of Language, Truth, and Logic in which he defended the main doctrines of the book. In the ten years following the publication of the first edition, the principle of verificationism, the view that metaphysical assertions are meaningless, and Ayer’s emotivism had all come under attack. Despite his vigorous defense, logical positivism’s influence was already waning, and by the mid-1950’s it had been eclipsed in the English-speaking world by ordinary-language philosophy, W. V. O. Quine’s scientific naturalism, and Ludwig Wittgenstein’s later work. Although logical positivism is no longer a living philosophical movement, Language, Truth, and Logic remains a superb introduction to doctrines that exerted an enormous influence on the evolution of twentieth century analytic philosophy.

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