Alfred Jules Ayer (1910-89) was a British philosopher who taught at University College, London and at the University of Oxford. His writings included Language, Truth and Logic (1936), Foundations of Empirical Knowledge (1940), Thinking and Meaning (1947), The Problem of Knowledge (1954), The Concept of a Person and other Essays (1963), Metaphysics and Common Sense (1969), Probablity and Evidence (1972), and The Central Questions of Knowledge (1972).
Language, Truth and Logic defines the verification principle of logical positivism. It discusses the uses and applications of the verification principle as an instrument of logical analysis. There are eight chapters: (1) “The Elimination of Metaphysics,” (2) “The Function of Philosophy,” (3) “The Nature of Philosophical Analysis,” (4) “The A Priori,” (5) “Truth and Probability,” (6) “Critique of Ethics and Theology,” (7) “The Self and the Common World,” and (8) “Solutions of Outstanding Philosophical Disputes.”
According to Ayer, the principle of verifiability is a criterion of meaning that requires every meaningful statement to be capable of being verified. Statements whose truth or falsehood cannot be verified are meaningless. Statements that have no literal meaning may have an emotional meaning, but they do not express propositions that can be analytically or empirically verified.
Analytic statements are tautologies (they are true by definition, necessarily true, and true under all conditions). The truth of analytic statements depends only on the meaning of their constituent elements, and it does not depend on confirmation by empirical testing.1
Synthetic statements (including empirical propositions) assert or deny something about the real world. The validity of synthetic statements is not established merely by the definition of the words or symbols that they contain. If a synthetic statement expresses an empirical proposition, then the validity of the proposition is established by its empirical verifiability.
Propositions are statements that have conditions under which they can be verified. According to the verification principle, meaningful statements have conditions under which their validity can be affirmed or denied. Statements that are not meaningful cannot be expressed as propositions. Every proposition is meaningful, and must be either true or false. Every empirical proposition asserts or denies something about the real world.
Are there limits to the verifiability of propositions? The possibility of "strong" or "weak" verification depends on how conclusively a proposition is capable of being verified. Strong (conclusive) verification is not possible for any empirical proposition, because the validity of any empirical proposition always depends upon further experience.2 However, weak (probable) verification is possible for any empirical proposition.
The theoretical or practical verifiability of a proposition depends on whether the proposition is verifiable in principle or in fact. Propositions for which we do not have a practical means of verification may still be meaningful if we can theoretically verify them.
A statement is factually meaningful if and only if it is empirically verifiable in theory or in practice. A statement is literally meaningful if and only if it expresses a proposition. Factual meaning is a property of statements that are meaningful without being analytic.3 Literal meaning is a property of statements that are analytically or empirically verifiable.
The propositions of philosophy are analytic, because they are concerned with relations of ideas, but the propositions of science are empirical, because they are concerned with matters of fact. The task of philosophy, says Ayer, is to clarify the logical relationships of empirical propositions. If the meaning of propositions is defined by their verifiability, then philosophy cannot establish the truth or falsehood of metaphysical statements that cannot be empirically verified, because these statements have no literal meaning.4
Ayer criticizes the notion that philosophy may provide us with knowledge of truths that transcend analytic or empirical inquiry. He says that metaphysical arguments about objects that are beyond the limits of possible experience are not meaningful.5 He dismisses such statements as nonsense, because they are not analytically or empirically verifiable, and because they cannot be subjected to criteria of truth or falsehood.6
The primary function of philosophy, says Ayer, is neither to propose basic principles of knowledge nor to construct a deductive system of meaningful propositions by offering the consequences of such principles as a complete picture of reality.7 The primary function of philosophy is to clarify the logical relations of empirical propositions. However, Ayer's position may be susceptible to the criticism that if the verification principle itself is a basic principle of knowledge, then the assertion that the purpose of philosophy is not to define basic principles of knowledge is self-contradictory.
Ayer agrees with Hume that propositions may be divided into two kinds: those that concern "relations of ideas," and those that concern "matters of fact." Propositions that concern relations of ideas include the a priori propositions of logic and mathematics.8 Propositions that concern matters of fact include empirical or a posteriori propositions.
Propositions that concern matters of fact can never be shown to be necessarily true, says Ayer, because there is always a possibility that they may be disproved by further empirical testing. Necessary truth can only belong to propositions that concern relations of ideas, because the truth of such propositions is analytic and not empirical.
Ayer rejects the rationalistic assertion that empirical truths are deducible from a priori propositions. A priori propositions may have a literal meaning, but they do not have a factual meaning. Propositions that are factually meaningful cannot be deduced from propositions that are not factually meaningful. They can only be deduced from the facts of experience or from other propositions that are deducible from the facts of experience.
Ayer also modifies Kant’s explanation of the difference between analytic and synthetic propositions by saying that a proposition can be described as analytic if its validity depends only on the definitions of the symbols it contains, while a proposition can be described as synthetic if its validity is determined by the facts of experience.9
Analytic propositions may provide us with new knowledge of the logical relations of propositions. However, analytic propositions do not provide us with any new knowledge of matters of fact, because the validity of analytic propositions does not depend on empirical evidence.10
Truth is a criterion by which propositions may be validated, but it is not a quality or relation. To say that a proposition is true is merely to assert it, and to say that a proposition is false is merely to assert a contradictory proposition. Thus, truth and falsehood are merely signs of assertion or denial of propositions.11
Assertions of value have literal meaning only insofar as they are verifiable. If an ethical or aesthetic judgment cannot be subjected to empirical testing, then it has no literal meaning. Empirical testing may be theoretical or practical.
Ethical and aesthetic judgments are not objective, says Ayer, and therefore cannot be proven to be true or false. They express feelings, but do not express propositions, and thus they have no objective validity. They are not analytic, and they have no literal or factual meaning.
When we question the truth of an ethical or aesthetic judgment, what we are actually calling into question are the propositions on which that judgment is based (or the logical interpretation of those propositions). We cannot argue about something that cannot be expressed as a proposition. We can only argue about something that can be analytically or empirically verified.
Metaphysical statements, such as statements about the existence or nonexistence of God, are therefore factually meaningless, and have no objective validity. Such statements can neither be proved nor be disproved, and they can neither be validated nor be invalidated by empirical testing.
Ayer’s logical empiricism may be applied to many areas of theoretical and practical inquiry, and it may provide a method of putting an end to philosophical disputes that otherwise would be unresolvable. He emphasizes that philosophy should not be regarded as a metaphysical concern or an attempt to provide speculative truths about the nature of ultimate reality. Rather, philosophy should be regarded as an analysis of the logical relations of propositions. It should be noted, however, that the verification principle may in some cases be used as a method of arbitrarily rejecting as meaningless any abstract concept or belief system that cannot be conclusively proved to be true or false. Ayer’s radical empiricism may define such concepts or belief systems as having no literal meaning, and it may thus become a radical skepticism. Ethics, aesthetics, and religion may all be regarded as literally meaningless.
Ayer explains that the verification principle is a criterion of the meaningfulness of propositions, and that it itself is not an empirical proposition. He also admits that there may be other criteria of the meaningfulness of propositions. However, there still remains the problem that while he asserts that meaningfulness depends on analytic or empirical verifiability, the meaningfulness of the verification principle itself may not be capable of being analytically or empirically verified.
1Alfred Jules Ayer, Language, Truth and Logic (New York: Dover Publications, 1952), p. 16.
2Ibid., p. 9.
3Ibid., p. 15.
4Ibid., p. 31.
5Ibid., pp. 31-32.
6Ibid., p. 44.
7Ibid., p. 46.
8Ibid., p. 78.
9Ibid., p. 80.
10Ibid., pp. 88-89.
Ayer, Alfred Jules. Language, Truth, and Logic. New York: Dover Publications, 1952.