Logical positivism
Logical positivism, later called logical empiricism, and both of which together are also known as neopositivism, is a movement whose central thesis is the verification principle (also known as the verifiability criterion of meaning).[1] This theory of knowledge asserts that only statements verifiable through direct observation or logical proof are meaningful in terms of conveying truth value, information or factual content. Starting in the late 1920s, groups of philosophers, scientists, and mathematicians formed the Berlin Circle and the Vienna Circle, which, in these two cities, would propound the ideas of logical positivism.
Flourishing in several European centres through the 1930s, the movement sought to prevent confusion rooted in unclear language and unverifiable claims by converting philosophy into "scientific philosophy", which, according to the logical positivists, ought to share the bases and structures of empirical sciences' best examples, such as Albert Einstein's general theory of relativity.[2] Despite its ambition to overhaul philosophy by studying and mimicking the extant conduct of empirical science, logical positivism became erroneously stereotyped as a movement to regulate the scientific process and to place strict standards on it.[2]
After World War II, the movement shifted to a milder variant, logical empiricism, led mainly by Carl Hempel, who, during the rise of Nazism, had emigrated to the United States. In the ensuing years, the movement's central premises, still unresolved, were heavily criticised by leading philosophers, particularly Willard van Orman Quine and Karl Popper, and even, within the movement itself, by Hempel. The 1962 publication of Thomas Kuhn's landmark book The Structure of Scientific Revolutions dramatically shifted academic philosophy's focus. In 1967 philosopher John Passmore pronounced logical positivism "dead, or as dead as a philosophical movement ever becomes".[3]
Origins[edit]
Logical positivists picked from Ludwig Wittgenstein's early philosophy of language the verifiability principle or criterion of meaningfulness. As in Ernst Mach's phenomenalism, whereby the mind knows only actual or potential sensory experience, verificationists took all sciences' basic content to be only sensory experience. And some influence came from Percy Bridgman's musings that others proclaimed as operationalism, whereby a physical theory is understood by what laboratory procedures scientists perform to test its predictions. In verificationism, only the verifiable was scientific, and thus meaningful (or cognitively meaningful), whereas the unverifiable, being unscientific, were meaningless "pseudostatements" (just emotively meaningful). Unscientific discourse, as in ethics and metaphysics, would be unfit for discourse by philosophers, newly tasked to organize knowledge, not develop new knowledge.
Definitions[edit]
Logical positivism is sometimes stereotyped as forbidding talk of unobservables, such as microscopic entities or such notions as causality and general principles,[4] but that is an exaggeration. Rather, most neopositivists viewed talk of unobservables as metaphorical or elliptical: direct observations phrased abstractly or indirectly. So theoretical terms would garner meaning from observational terms via correspondence rules, and thereby theoretical laws would be reduced to empirical laws. Via Bertrand Russell's logicism, reducing mathematics to logic, physics' mathematical formulas would be converted to symbolic logic. Via Russell's logical atomism, ordinary language would break into discrete units of meaning. Rational reconstruction, then, would convert ordinary statements into standardized equivalents, all networked and united by a logical syntax. A scientific theory would be stated with its method of verification, whereby a logical calculus or empirical operation could verify its falsity or truth.
Development[edit]
In the late 1930s, logical positivists fled Germany and Austria for Britain and the United States. By then, many had replaced Mach's phenomenalism with Otto Neurath's physicalism, whereby science's content is not actual or potential sensations, but instead consists of entities that are publicly observable. Rudolf Carnap, who had sparked logical positivism in the Vienna Circle, had sought to replace verification with simply confirmation. With World War II's close in 1945, logical positivism became milder, logical empiricism, led largely by Carl Hempel, in America, who expounded the covering law model of scientific explanation. Logical positivism became a major underpinning of analytic philosophy,[5] and dominated philosophy in the English-speaking world, including philosophy of science, while influencing sciences, but especially social sciences, into the 1960s. Yet the movement failed to resolve its central problems,[6][7][8] and its doctrines were increasingly criticized, most trenchantly by Willard Van Orman Quine, Norwood Hanson, Karl Popper, Thomas Kuhn, and Carl Hempel.
Roots[edit]
Language[edit]
Tractatus Logico-Philosophicus, by the young Ludwig Wittgenstein, introduced the view of philosophy as "critique of language", offering the possibility of a theoretically principled distinction of intelligible versus nonsensical discourse. Tractatus adhered to a correspondence theory of truth (versus a coherence theory of truth). Wittgenstein's influence also shows in some versions of the verifiability principle.[9][10] In tractarian doctrine, truths of logic are tautologies, a view widely accepted by logical positivists who were also influenced by Wittgenstein's interpretation of probability although, according to Neurath, some logical positivists found Tractatus to contain too much metaphysics.[11]
Logicism[edit]
Gottlob Frege began the program of reducing mathematics to logic, continued it with Bertrand Russell, but lost interest in this logicism, and Russell continued it with Alfred North Whitehead in their Principia Mathematica, inspiring some of the more mathematical logical positivists, such as Hans Hahn and Rudolf Carnap.[12] Carnap's early anti-metaphysical works employed Russell's theory of types.[13] Carnap envisioned a universal language that could reconstruct mathematics and thereby encode physics.[12] Yet Kurt Gödel's incompleteness theorem showed this impossible except in trivial cases, and Alfred Tarski's undefinability theorem shattered all hopes of reducing mathematics to logic.[12] Thus, a universal language failed to stem from Carnap's 1934 work Logische Syntax der Sprache (Logical Syntax of Language).[12] Still, some logical positivists, including Carl Hempel, continued support of logicism.[12]
Empiricism[edit]
In Germany, Hegelian metaphysics was a dominant movement, and Hegelian successors such as F H Bradley explained reality by postulating metaphysical entities lacking empirical basis, drawing reaction in the form of positivism.[14] Starting in the late 19th century, there was a "back to Kant" movement. Ernst Mach's positivism and phenomenalism were a major influence.[15]
History[edit]
Vienna[edit]
The Vienna Circle, gathering around University of Vienna and Café Central, was led principally by Moritz Schlick. Schlick had held a neo-Kantian position, but later converted, via Carnap's 1928 book Der logische Aufbau der Welt, that is, The Logical Structure of the World. A 1929 pamphlet written by Otto Neurath, Hans Hahn, and Rudolf Carnap summarized the Vienna Circle's positions. Another member of Vienna Circle to later prove very influential was Carl Hempel. A friendly but tenacious critic of the Circle was Karl Popper, whom Neurath nicknamed the "Official Opposition".
Carnap and other Vienna Circle members, including Hahn and Neurath, saw need for a weaker criterion of meaningfulness than verifiability.[16] A radical "left" wing—led by Neurath and Carnap—began the program of "liberalization of empiricism", and they also emphasized fallibilism and pragmatics, which latter Carnap even suggested as empiricism's basis.[16] A conservative "right" wing—led by Schlick and Waismann—rejected both the liberalization of empiricism and the epistemological nonfoundationalism of a move from phenomenalism to physicalism.[16] As Neurath and somewhat Carnap posed science toward social reform, the split in Vienna Circle also reflected political views.[16]
Berlin[edit]
The Berlin Circle was led principally by Hans Reichenbach.
Rivals[edit]
Both Moritz Schlick and Rudolf Carnap had been influenced by and sought to define logical positivism versus the neo-Kantianism of Ernst Cassirer—the then leading figure of Marburg school, so called—and against Edmund Husserl's phenomenology. Logical positivists especially opposed Martin Heidegger's obscure metaphysics, the epitome of what logical positivism rejected. In the early 1930s, Carnap debated Heidegger over "metaphysical pseudosentences".[17]
Export[edit]
As the movement's first emissary to the New World, Moritz Schlick visited Stanford University in 1929, yet otherwise remained in Vienna and was murdered in 1936 at the University by a former student, Johann Nelböck, who was reportedly deranged.[17] That year, a British attendee at some Vienna Circle meetings since 1933, A. J. Ayer saw his Language, Truth and Logic, written in English, import logical positivism to the English-speaking world. By then, the Nazi Party's 1933 rise to power in Germany had triggered flight of intellectuals.[17] In exile in England, Otto Neurath died in 1945.[17] Rudolf Carnap, Hans Reichenbach, and Carl Hempel—Carnap's protégé who had studied in Berlin with Reichenbach—settled permanently in America.[17] Upon Germany's annexation of Austria in 1938, remaining logical positivists, many of whom were also Jewish, were targeted and continued flight. Logical positivism thus became dominant in the English-speaking world.
Principles[edit]
Analytic/synthetic gap[edit]
Concerning reality, the necessary is a state true in all possible worlds—mere logical validity—whereas the contingent hinges on the way the particular world is. Concerning knowledge, the a priori is knowable before or without, whereas the a posteriori is knowable only after or through, relevant experience. Concerning statements, the analytic is true via terms' arrangement and meanings, thus a tautology—true by logical necessity but uninformative about the world—whereas the synthetic adds reference to a state of facts, a contingency.[18][19]
In 1739, David Hume cast a fork aggressively dividing "relations of ideas" from "matters of fact and real existence", such that all truths are of one type or the other.[20][21] By Hume's fork, truths by relations among ideas (abstract) all align on one side (analytic, necessary, a priori), whereas truths by states of actualities (concrete) always align on the other side (synthetic, contingent, a posteriori).[20] Of any treatises containing neither, Hume orders, "Commit it then to the flames, for it can contain nothing but sophistry and illusion".[20]
Thus awakened from "dogmatic slumber", Immanuel Kant quested to answer Hume's challenge—but by explaining how metaphysics is possible. Eventually, in his 1781 work, Kant crossed the tines of Hume's fork to identify another range of truths by necessity—synthetic a priori, statements claiming states of facts but known true before experience—by arriving at transcendental idealism, attributing the mind a constructive role in phenomena by arranging sense data into the very experience space, time, and substance. Thus, Kant saved Newton's law of universal gravitation from Hume's problem of induction by finding uniformity of nature to be a priori knowledge. Logical positivists rejected Kant's synthetic a priori, and adopted Hume's fork, whereby a statement is either analytic and a priori (thus necessary and verifiable logically) or synthetic and a posteriori (thus contingent and verifiable empirically).[20]
Observation/theory gap[edit]
Early, most logical positivists proposed that all knowledge is based on logical inference from simple "protocol sentences" grounded in observable facts. In the 1936 and 1937 papers "Testability and meaning", individual terms replace sentences as the units of meaning.[16] Further, theoretical terms no longer need to acquire meaning by explicit definition from observational terms: the connection may be indirect, through a system of implicit definitions.[16] Carnap also provided an important, pioneering discussion of disposition predicates.[16]
Decline and legacy[edit]
By the late 1960s, logical positivism had become exhausted.[51] In 1976, A. J. Ayer quipped that "the most important" defect of logical positivism "was that nearly all of it was false", though he maintained "it was true in spirit."[52][53] Although logical positivism tends to be recalled as a pillar of scientism,[54] Carl Hempel was key in establishing the philosophy subdiscipline philosophy of science[17] where Thomas Kuhn and Karl Popper brought in the era of postpositivism.[49] John Passmore found logical positivism to be "dead, or as dead as a philosophical movement ever becomes".[52]
Logical positivism's fall reopened debate over the metaphysical merit of scientific theory, whether it can offer knowledge of the world beyond human experience (scientific realism) versus whether it is but a human tool to predict human experience (instrumentalism).[55][56] Meanwhile, it became popular among philosophers to rehash the faults and failures of logical positivism without investigation of them.[57] Thereby, logical positivism has been generally misrepresented, sometimes severely.[58] Arguing for their own views, often framed versus logical positivism, many philosophers have reduced logical positivism to simplisms and stereotypes, especially the notion of logical positivism as a type of foundationalism.[58] In any event, the movement helped anchor analytic philosophy in the English-speaking world, and returned Britain to empiricism. Without the logical positivists, who have been tremendously influential outside philosophy, especially in psychology and other social sciences, intellectual life of the 20th century would be unrecognizable.[17]
Articles by logical positivists
Articles on logical positivism
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