Logical positivism (also called logical empiricism and neo-positivism) is a school of philosophy that combines empiricism – the idea that observational evidence is indispensable for knowledge of the world – with a version of rationalism incorporating mathematical and logico-linguistic constructs and deductions in epistemology.[1]
Logical positivism grew from the discussions of a group called the "First Vienna Circle" which gathered at the Café Central before World War I. After the war Hans Hahn, a member of that early group, helped bring Moritz Schlick to Vienna. Schlick's Vienna Circle, along with Hans Reichenbach's Berlin Circle, propagated the new doctrines more widely in the 1920s and early 1930s. It was Otto Neurath's advocacy that made the movement self-conscious and more widely known. A 1929 pamphlet written by Neurath, Hahn, and Rudolf Carnap summarized the doctrines of the Vienna Circle at that time. The doctrines included the opposition to all metaphysics, especially ontology and synthetic a priori propositions; the rejection of metaphysics not as wrong but as having no meaning; a criterion of meaning based on Ludwig Wittgenstein's early work; the idea that all knowledge should be codifiable in a single standard language of science; and above all the project of "rational reconstruction," in which ordinary-language concepts were gradually to be replaced by more precise equivalents in that standard language.
In the early 1930s, the Vienna Circle dispersed, mainly because of political upheaval and the untimely deaths of Hahn and Schlick. The most prominent proponents of logical positivism emigrated to United Kingdom and United States, where they considerably influenced American philosophy. Until the 1950s, logical positivism was the leading school in the philosophy of science. During this period of upheaval, Carnap proposed a replacement for the earlier doctrines in his "Logical Syntax of Language". This change of direction and the somewhat differing views of Reichenbach and others led to a consensus that the English name for the shared doctrinal platform, in its American exile from the late 1930s, should be "logical empiricism."
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The chief influences on the early logical positivists were the positivist Ernst Mach and the young 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 Logico-Philosophicus was a text of great importance for the positivists. The Tractatus introduced many doctrines which later influenced logical positivism, including the conception of philosophy as a "critique of language," and the possibility of drawing a theoretically principled distinction between intelligible and nonsensical discourse. The Tractatus also adhered to a correspondence theory of truth which the positivists adopted, although some, like Otto Neurath, preferred a form of coherentism. Wittgenstein's influence is further evident in certain formulations of the verification 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 "To state the circumstances under which a proposition is true is the same as stating its meaning."[2] The tractarian doctrine that the truths of logic are tautologies was widely held among the logical positivists. Wittgenstein also influenced the logical positivists' interpretation of probability. According to Neurath, some logical positivists disliked the Tractatus, since they thought it was full of metaphysics.[3]
Contemporary developments in logic and the foundations of mathematics, especially Bertrand Russell and Alfred North 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.[4]
Immanuel Kant also had an important influence on the positivists, both positive and negative. On the negative side, Kant was often treated by the positivists as something of a punching bag in their early debates, and Kant's doctrine of synthetic a priori truths was the doctrine they most wished to overthrow. On the positive side, Kant's views about the nature of physical objects pervaded the "protocol sentence" debate,[5] and Kantian views about the relationship between philosophy and science were shared by the positivists to some degree.[6]
Positivism in Germany is thought to have risen in response to Hegelian and neo-Hegelian metaphysics, which was the dominant philosophical view in Germany.[7] Hegelian successors such as F.H. Bradley attempted to explain reality by postulating metaphysical entities that did not have any empirical basis.[7] Logical positivists in response wanted to stop such metaphysical entities from being used as an explanation.
Another, less well-known factor that triggered logical positivism was the urgency of solving new philosophical issues raised by new scientific developments. The Vienna Circle under the influence of Moritz Schlick and the Berlin Circle under the influence of Reichenbach consisted of scientists, mathematicians, and scientists turned philosophers, who shared a common goal of solving newly raised problems in philosophy of science.
Although the logical positivists held a wide range of views on many matters, they were all interested in science and skeptical of theology and metaphysics. Early on, most logical positivists took the view that all knowledge is based on logical inference from simple "protocol sentences" grounded in observable facts. Many logical positivists supported forms of materialism, metaphysical naturalism, and empiricism.
Perhaps the view for which the logical positivists are best known is the verifiability criterion of meaning, or verificationism. In one of its earlier and stronger formulations, this is the doctrine that a proposition is "cognitively meaningful" only if there is a finite procedure for conclusively determining whether it is true or false.[8] An intended consequence of this view, for most logical positivists, is that metaphysical, theological, and ethical statements fall short of this criterion, and so are not cognitively meaningful.[9] They distinguished cognitive from other varieties of meaningfulness (e.g. emotive, expressive, figurative), and most authors concede that the non-cognitive statements of the history of philosophy possess some other kind of meaningfulness. The positive characterization of cognitive meaningfulness varies from author to author. It has been described as the property of having a truth value, corresponding to a possible state of affairs, naming a proposition, or being intelligible or understandable in the sense in which scientific statements are intelligible or understandable.[10]
Another characteristic feature of logical positivism is the commitment to "Unified Science"; that is, the development of a common language or, in Neurath's phrase, a "universal slang" in which all scientific propositions can be expressed.[11] The adequacy of proposals or fragments of proposals for such a language was often asserted on the basis of various "reductions" or "explications" of the terms of one special science to the terms of another, putatively more fundamental one. Sometimes these reductions took the form of set-theoretic manipulations of a handful of logically primitive concepts;[12] sometimes these reductions took the form of allegedly analytic or a priori deductive relationships.[13] A number of publications over a period of thirty years would attempt to elucidate this concept.
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 universal claims ("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, 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.
Logical positivists' response to the first criticism was 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."
Many commentators (including the preceding section) 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.
Karl Popper was a well-known critic of logical positivism, who published the book Logik der Forschung in 1934 (translated by himself as The Logic of Scientific Discovery, published 1959). In it he argued that the positivists' criterion of verifiability was too strong a criterion for science, and should be replaced by a criterion of falsifiability. Popper thought that falsifiability was a better criterion because it did not invite the philosophical problems inherent in verifying an induction, and it allowed statements from the physical sciences which seemed scientific but which did not meet the verification criterion.
Popper's concern was not with distinguishing meaningful from meaningless statements, but distinguishing scientific from metaphysical statements. Unlike the positivists, he did not hold that metaphysical statements must be meaningless; he also held that a statement which was "metaphysical" and unfalsifiable in one century (like the ancient Greek philosophy about atoms) could, in another century, be developed into falsifiable theories that have the metaphysical views as a consequence, and thus become scientific.
Popper denied that science need rely on inductive reasoning, or that inductive reasoning actually exists, although most philosophers think it obvious that science does rely on it.[14]
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.
According to Hilary Putnam, a former student of Hans Reichenbach and Rudolf Carnap, making an observational/theoretical distinction is meaningless. The "received view" operates on the correspondence rule that states "The observational terms are taken as referring to specified phenomena or phenomenal properties, and the only interpretation given to the theoretical terms is their explicit definition provided by the correspondence rules."[7] Putnam argues that introducing this dichotomy of observational terms and theoretical terms is the problem to start from.[15] Putnam demonstrates this with four objections:
Subsequent philosophy of science tends to make use of certain aspects of both of these approaches. W. V. O. Quine criticized the distinction between analytic and synthetic statements and the reduction of meaningful statements to immediate experience. Work by Thomas Kuhn has claimed 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 spread throughout almost the entire western world. It was disseminated throughout the European continent. It was spread to Britain by the influence of A. J. Ayer. And later, it was brought to American universities by members of the Vienna Circle after they fled Europe and settled in the United States during and after WWII.
Logical positivism was essential to the development of early analytic philosophy. 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.
In the mid-twentieth century, logical positivism (logical empiricism) dominated a great deal of philosophy in America and elsewhere in the English-speaking world. The usage of the name in academia declined in the mid-1960s and has been seldom used in new work since the late 1970s. The decline has been attributed to a range of factors, including changes in the school of language philosophy brought about by Ludwig Wittgenstein, stress from W.V. Quine's holism, issues arising from logical positivism's notably positive stance on inductive logic, growing respect for fields such as the history of science that take over much of logical positivism's earlier roles, the rise of instrumentalism, and "eventually there was pressure from scientific realism."[16] There was also a growing awareness of the difficulty of evading theory-ladenness of observation statements, as implied in Hilary Putnam's objection. Perhaps more important, however, has been the incorporation of its ideas into the mathematical and logical formalisms developed in many fields without always citing their historical legacy.
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