Language, Truth and Logic is a 1936 book about meaning by the philosopher Alfred Jules Ayer, in which the author defines, explains, and argues for the verification principle of logical positivism, sometimes referred to as the criterion of significance or criterion of meaning. Ayer explains how the principle of verifiability may be applied to the problems of philosophy. Language, Truth and Logic brought some of the ideas of the Vienna Circle and the logical empiricists to the attention of the English-speaking world.
Historical background According to Ayer's autobiographical book, Part of My Life, it was work he started in the summer and autumn of 1933 that eventually led to Language, Truth and Logic, specifically Demonstration of the Impossibility of Metaphysics—later published in Mind under the editorship of G.E. Moore. The title of the book was taken ("To some extent plagiarized" according to Ayer) from Friedrich Waismann's Logik, Sprache, Philosophie.
Criterion of meaning According to Ayer, analytic statements are tautologies. A tautology is a statement that is necessarily true, true by definition, and true under any conditions. A tautology is a repetition of the meaning of a statement, using different words or symbols. According to Ayer, the statements of logic and mathematics are tautologies. Tautologies are true by definition, and thus their validity does not depend on empirical testing. Synthetic statements, or 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 they contain. According to Ayer, if a 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. By 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 verifiable proposition is meaningful, although it may be either true or false. Every proposition asserts or denies something, and thus is either true or false.
Types of verification Ayer distinguishes between ‘strong’ and ‘weak’ verification, noting that there is a limit to how conclusively a proposition can be verified. ‘Strong’ (fully conclusive) verification is not possible for any empirical proposition, because the validity of any proposition always depends upon further experience. ‘Weak’ (probable) verification, on the other hand, is possible for any empirical proposition. Ayer also distinguishes between practical and theoretical verifiability. Propositions for which we do not have a practical means of verification may still be meaningful if we can verify them in principle. Literal meaning must also be distinguished from factual meaning. Literal meaning is an attribute of statements that are either analytic or empirically verifiable. Factual meaning is an attribute of statements that are meaningful without being analytic. Thus, statements that have factual meaning say something about the real world. Ayer agrees with Hume that there are two main classes of propositions: those that concern 'relations of ideas,' and those that concern 'matters of fact.' Propositions about 'relations of ideas' include the a priori propositions of logic and mathematics. Propositions about 'matters of fact,' on the other hand, make assertions about the empirical world. Ayer argues that philosophic propositions are analytic, and that they are concerned with 'relations of ideas.' The task of philosophy is to clarify the logical relationships of empirical propositions. If the meaning of propositions is defined by verifiability, then philosophy cannot provide speculative truths about metaphysical statements that cannot be empirically verified.
Metaphysics attacked Ayer rejects the metaphysical thesis that philosophy can give us knowledge of a transcendent reality. He dismisses metaphysical arguments, calling them nonsense, and saying that they cannot be empirically verified. He argues that metaphysical statements have no literal meaning, and that they cannot be subjected to criteria of truth or falsehood. A significant consequence of abandoning metaphysics as a concern of philosophy is a rejection of the view that the function of philosophy is to propose basic principles of meaning and to construct a deductive system by offering the consequences of these principles of meaning as a complete picture of reality. But this is, some may argue, what Ayer does, in presenting the principle of verifiability as a criterion of meaningfulness for any empirical proposition. According to Ayer, no proposition concerning "matters of fact" can ever be shown to be necessarily true, because there is always a possibility that it may be refuted by further empirical testing. Logical certainty is possible only for analytic observations, which are tautologies, and not for empirical observations concerning "matters of fact." Ayer explains that his radical empiricism is opposed to rationalism. Rationalism asserts that there are truths about the world that can be known by a priori reasoning, or independently of experience. According to the principle of verifiability, propositions about 'matters of fact' can be meaningful only if they are capable of being empirically verified. Ayer agrees with, and elaborates on, Kant's explanation of the distinction between analytic and synthetic judgments. According to Ayer, a proposition is analytic if its validity depends only on the definitions of the symbols it contains. A proposition is synthetic if its validity is determined by the facts of experience. Analytic observations give us new knowledge, because they reveal unsuspected implications of our statements and beliefs. But analytic observations do not give us new knowledge of matters of fact, because they only tell us what is already known.
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