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Logical positivism (later referred to as logical empiricism, rational empiricism, or neo-positivism) is a school of philosophy that combines positivism—which states that the only authentic knowledge is scientific knowledge—with a version of apriorism—the notion that some propositions can be held true without empirical support. A central tenet of logical positivism is that metaphysical, theological, and ethical sentences are "cognitively meaningless," and serve merely to express the feelings or desires of a speaker. Only mathematical, logical and scientific statements are literally meaningful, or have truth values. Logical positivism originated in the Vienna Circle in the 1920s, where Rudolf Carnap, Otto Neurath, and others (see Philosophers associated with logical positivism in this article) divided meaningful statements into those which are analytic (true a priori), and those which are synthetic (verified by sensory experience, a posteriori)—this was perhaps presaged by Hume's fork. The logical positivists agreed that there are no synthetic a priori propositions, though they disagreed with earlier positivists, such as Ernst Mach, who held that the a priori had no place in science. Logical positivism holds that philosophy should aspire to the rigor of science. Philosophy should provide strict criteria for judging sentences true, false, and meaningless. The Origins of Logical Positivism The chief influences on the early logical positivists were Ernst Mach and Ludwig Wittgenstein. Mach's influence is most apparent in the logical positivists' persistent concern with metaphysics, the unity of science, and the interpretation of the theoretical terms of science, as well as the doctrines of reductionism and phenomenalism, later abandoned by many positivists. Wittgenstein's Tractatus was a text of great importance for the positivists. The use of the tools of modern logic for linguistic reform, the conception of philosophy as a "critique of language," and the possibility of drawing a theoretically principled distinction between intelligible and nonsensical discourse were all appealing to the logical positivists. Many positivists adopted a correspondence theory of truth similar to that of the Tractatus, although some, like Otto Neurath, preferred a form of coherentism. Wittgenstein's influence is further evident in certain formulations of the verifiability principle. Compare, for example, Proposition 4.024 of the Tractatus, where Wittgenstein asserts that we understand a proposition when we know what happens if it is true, with Schlick's assertion that "The definition of the circumstances under which a statement is true is perfectly 'equivalent' to the definition of its meaning". Recent developments in logic and the foundations of mathematics, especially Russell and Whitehead's monumental Principia Mathematica, impressed the more mathematically minded logical positivists such as Hans Hahn and Rudolf Carnap. "Language-planning" and syntactical techniques derived from these developments were used to defend logicism in the philosophy of mathematics and various reductionist theses. Russell's theory of types was employed to explosive effect in Carnap's early anti-metaphysical polemics. Immanuel Kant was something of a punching bag in many of the logical positivists' early debates, but his influence shows through. His doctrine of synthetic a priori truths was the view to overthrow, and his notion of the thing in itself commanded its fair share of attention. More positively, Kantian views about the nature of physical objects pervade the "protocol sentence" debate, and the positivists all shared somewhat Kantian views about the relationship between philosophy and science. The Basic Tenets of Logical Positivism Although the logical positivists held a wide range of beliefs on many matters, they were all interested in science and skeptical of theology and metaphysics. Early on, most logical positivists believed that all knowledge is based on logical inference from simple "protocol sentences" grounded in observable facts. Many logical positivists supported forms of materialism, philosophical naturalism, and empiricism. Logical positivism is perhaps best known for the verifiability criterion of meaning, which asserts that a statement is meaningful if and only if it is empirically verifiable. One intended consequence of the verification criterion is that all non-empirical forms of discourse, including ethics and aesthetics, are not "literally" or "cognitively" meaningful, and thus belong to "metaphysics". Unified Science An important objective pursued by logical positivism is "unified science"; that is, the construction of a "constitutive system" in which every legitimate statement is reduced to the concepts of a lower level which refer directly to a given experience. A number of publications over a period of thirty years would attempt to elucidate this concept. Einheitswissenschaft (Unified Science) The Vienna Circle published a collection called Einheitswissenschaft (Unified Science)—edited by Rudolf Carnap, Philipp Frank, Hans Hahn, Otto Neurath, Jorgen Jorgensen (after Hahn's death) and Charles Morris—the aim of which was to present a unified vision of science. The collection was dismissed, after the publication of several monographies, because of the problems arising from World War II. The list of philosophers and scientists who contributed to these works is impressive. The complete list of contributors is given here for the historical record. Einheitswissenschaft (Unified Science), edited by Carnap, Frank, Hahn, Neurath, Jorgensen (after Hahn's death), and Morris (from 1938): International Encyclopedia of Unified Science In 1938 the publication of the International Encyclopedia of Unified Science started under the auspice of logical positivists. It was an ambitious project, and never completed. Only the first section, Foundations of the Unity of Sciences, was published; it contained two volumes, for a total of twenty monographs published from 1938 to 1969: Perhaps the most famous work published in the International Encyclopedia of Unified Science is Thomas Kuhn's The Structure of Scientific Revolutions. However, every entry in the encyclopedia is of substantial scientific and philosophical value. Monographs on the Scientific World-Conception A third collection was published by the Vienna Circle from 1928 to 1937. This collection was entitled Schriften zur wissenschaftlichen Weltauffassung (Monographs on the Scientific World-Conception), and was edited by Schlick and Frank. Scientists and philosophers such as Karl Popper contributed. The contributors and monographs were: Philosophers associated with logical positivism There is an extensive list of philosophers who are associated to some degree with logical positivism. The Vienna Circle Germany and the Berlin Circle In Germany, members of the Berlin Circle contributed in an essential way to the development of logical positivism: Scandinavia United Kingdom Poland Reactions to Logical Positivism Early critics of logical positivism said that its fundamental tenets could not themselves be formulated in a way that was clearly consistent. The verifiability criterion of meaning did not seem verifiable; but neither was it simply a logical tautology, since it had implications for the practice of science and the empirical truth of other statements. This presented severe problems for the logical consistency of the theory. Another problem was that, while positive existential claims ("there is at least one human being") and negative universals ("not all ravens are black") allow for clear methods of verification (find a human or a non-black raven), negative existential claims and positive universal claims do not allow for verification. Universal claims could apparently never be verified: How can you tell that all ravens are black, unless you've hunted down every raven ever, including those in the past and future? This led to a great deal of work on induction, probability, and "confirmation", which combined verification and falsification. Karl Popper, a well-known critic of logical positivism, published the book Logik der Forschung in 1934 (translated by himself as The Logic of Scientific Discovery published 1959). In it he presented an influential alternative to the verifiability criterion of meaning, defining scientific statements in terms of falsifiability. First, though, Popper's concern was not with distinguishing meaningful from meaningless statements, but distinguishing "scientific" from "metaphysical" statements. He did not hold that metaphysical statements must be meaningless; neither did he hold that a statement that in one century was "metaphysical" while unfalsifiable (like the ancient Greek philosophy about atoms), could not in another century become "falsifiable" and thus "scientific". About psychoanalysis he thought something similar: in his day it offered no method for falsification, and thus was not falsifiable and not scientific. However, he did not exclude it being meaningful, nor did he say psychoanalysts were necessarily "wrong" (it only couldn't be proven either way: that would have meant it was falsifiable), nor did he exclude that one day psychoanalysis could evolve into something falsifiable, and thus "scientific". He was, in general, more concerned with scientific practice than with the logical issues that troubled the positivists. Second, although Popper's philosophy of science enjoyed great popularity for some years, if his criterion is construed as an answer to the question the positivists were asking, it turns out to fail in exactly parallel ways. Negative existential claims ("there are no unicorns") and positive universals ("all ravens are black") can be falsified, but positive existential and negative universal claims cannot. Logical positivists' response to the first criticism is that logical positivism is a philosophy of science, not an axiomatic system that can prove its own consistency (see Gödel's incompleteness theorem). Secondly, a theory of language and mathematical logic were created to answer what it really means to make statements like "all ravens are black". A response to the second criticism was provided by A. J. Ayer in Language, Truth and Logic, in which he sets out the distinction between "strong" and "weak" verification. "A proposition is said to be verifiable, in the strong sense of the term, if, and only if, its truth could be conclusively established by experience." (Ayer 1946:50) It is this sense of verifiable that causes the problem of verification with negative existential claims and positive universal claims. However, the weak sense of verification states that a proposition is "verifiable... if it is possible for experience to render it probable" (ibid.). After establishing this distinction, Ayer goes on to claim that "no proposition, other than a tautology, can possibly be anything more than a probable hypothesis" (Ayer 1946:51), and therefore can only be subject to weak verification. This defense was controversial among logical positivists, some of whom stuck to strong verification, and claimed that general propositions were indeed nonsense. Subsequent philosophy of science tends to make use of certain aspects of both of these approaches. Work by W. V. O. Quine and Thomas Kuhn has convinced many that it is not possible to provide truth conditions for science independent of its historical paradigm. But even this criticism was not unknown to the logical positivists: Otto Neurath compared science to a boat which we must rebuild on the open sea. Logical positivism was essential to the development of early analytic philosophy. It was disseminated throughout the European continent and, later, in American universities by the members of the Vienna Circle. A.J. Ayer is considered responsible for the spread of logical positivism to Britain. The term subsequently came to be almost interchangeable with "analytic philosophy" in the first half of the twentieth century. Logical positivism was immensely influential in the philosophy of language and represented the dominant philosophy of science between World War I and the Cold War. Many subsequent commentators on "logical positivism" have attributed to its proponents a greater unity of purpose and creed than they actually shared, overlooking the complex disagreements among the logical positivists themselves. Footnotes Further Reading To the Icy Slopes of Logic. New York: Cambridge University Press, 2005. People Institutions Other philosophical movements About logical positivism About philosophical subjects pertinent to logical positivism | |||||||
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