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Logical Positivism

Shortly after the end of the first World War, a group of mathematicians, scientists, and philosophers began meeting in Vienna to discuss the implications of recent developments in logic, including Wittgenstein's Tractatus. Under the leadership of Moritz Schlick, this informal gathering (the "Vienna Circle") campaigned for a systematic reduction of human knowledge to logical and scientific foundations. Because the resulting logical positivism (or "logical empiricism") allowed only for the use of logical tautologies and first-person observations from experience, it dismissed as nonsense the metaphysical and normative pretensions of the philosophical tradition. Although participants sometimes found it difficult to defend the strict principles on which their programme depended, this movement offered a powerful vision of the possibilities for modern knowledge.

During the thirties, many of the younger positivists left Europe for England and the United States, where their influence over succeeding generations was enormous. Herbert Feigl and Otto Neurath concentrated on the philosophy of science, developing and refining systematic principles for study of the natural world. Mathematician Kurt Gödel used sophisticated reasoning to explore the limits of the logicist programme. Others became interested in the philosophy of language: Gustav Bergmann continued efforts to achieve a perspicuous representation of reality through an ideal logical language, while Friedrich Waismann began to examine the analysis of ordinary language.

Verifiability and Meaning

British philosopher A. J. Ayer presented many of the central doctrines of the positivist movement in his 1936 book, Language, Truth, and Logic. Ayer's polemical writing tried to show how the principle of verification could be used as a tool for the elimination of nonsense of every sort. In Ayer's formulation, the principle itself is a simple test:

We say that a sentence is factually significant to any given person, if and only if, [she or] he knows how to verify the proposition which it purports to express—that is, if [she or] he knows what observations would lead [her or] him, under certain conditions, to accept the proposition as being true, or reject it as being false.
Like the pragmatic theory put forward by Peirce, verificationism proposes that assertions are meaningful only when their content meets a (minimal) condition about the ways in which we would go about determining their truth. Moreover, like Hume's distinction between matters of fact and relations of ideas, the principle leaves no room for anything other than verifiable empirical observations of the natural world and the meaningless but useful tautologies of logic and mathematics.

Thus, much of Ayer's book was negative, emphasizing the consequences of a strict application of the positivist program to human pretensions at transcendental knowledge. Traditional metaphysics, with its abstract speculation about the supposed nature of reality, cannot be grounded on scientific observation, and is therefore devoid of significance. For the same reason, traditional religious claims are meaningless since it is impossible to state any observable circumstances under which we could be sure—one way or the other—about their truth. Even much of traditional epistemology is likely to fail the test; only the psychological study of observable human behavior regarding beliefs will remain. Mathematics and natural science are secure, but little else remains.

Although Ayer, Hempel, and other positivists spent a great deal of energy on technical refinements of the principle of verification, its basic content continued to guide the direction of the positivist movement. The major point is that much of what we try to say is meaningless blather.

The Logical Construction of the World

On a more positive note, the positivists supposed that what remains—consistent logical and mathematical reasoning, together with cautious observation of nature—comprises a great deal of worthwhile human knowledge. Rudolf Carnap's Der logische Aufbau der Welt (The Logical Structure of the World) (1929) outlined the world-view that is likely to result from a thorough application of the positivist program. The logical rigor of articles like "Testability and Meaning" (1936-37) illustrates both the power and the limitations of this procedure.

Carnap begins with an account of the methods and procedures by means of which we employ sensory observations to verify (or at least to confirm) the truth of scientific hypotheses about the operation of the physical universe. Using the formal methods of mathematical logic, then, the goal is to construct a strictly scientific language that perspicuously represents the structure of the world as a whole. The details are highly technical, of course, but it is only with the detailed treatment that the difficulties of the procedure become evident. The fundamental problem is that empirical generalizations are themselves incapable of direct support within such a system.

This was a crucial part of the insight of Karl Popper, another Viennese philosopher of science. Popper proposed abandonment of the quest for verification, noting that the key feature of scientific hypotheses is precisely their falsifiability rather than their confirmation. We best know what we mean when we carefully state the conditions under which we would be forced to give up what we have supposed.

Ethical Emotivism

The central tenets of logical positivism clearly have serious consequences when applied to moral philosophy. Attributions of value are not easily verifiable, so moral judgments may be neither true nor false, but as meaningless as those of metaphysics. Among the original members of the Vienna Circle, only Moritz Schlick devoted any attention to ethics at all, and he regarded it as the descriptive task of cataloging the ways in which members of a society express their feelings about human behavior of various sorts.

It was the American philosopher C.L. Stevenson who worked out the full implications of postivistic theories for expressions of moral praise or blame. The most vital issue to be considered is the meta-ethical question of what moral terms mean. Although Moore had correctly noted that good cannot be defined simply in terms of the approval of human beings, Stevenson made the even more radical suggestion that moral judgments have no factual content at all. Analysis of moral language should focus instead on its unique function as a guide to human behavior, what Stevenson called the "magnetism" of moral terms.

In "The Emotive Meaning of Ethical Terms" (1937) Stevenson argued that we must distinguish clearly between the descriptive or cognitive content of a term and its non-descriptive or emotive meaning. At a purely literal descriptive level, statements about moral value are indeed unverifiable and therefore meaningless, but considered as appeals to human emotions, they may have powerful dynamic effects. Saying "Murder is wrong," may have no factual significance, but it does succinctly convey a host of expressive suggestions, including (at least) "I don't like murder," "You shouldn't like murder," and "We should disapprove of murderers." Stevenson's ethical emotivism, further developed in Ethics and Language (1944), quickly became an influential twentieth-century noncognitivist theory about the meaning of moral language.

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