Version of empiricism applying to the meanings of words or sentences, whereby they have meaning only if there are rules involving sense-experience for applying or verifying them; the rules may also constitute the meaning. (Analytic sentences – that is, roughly, those made true or false by logical considerations – are excepted.)
Akin to, though some say slightly less rigorous than, logical positivism.
Logical positivists culled 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.
Logical positivism is sometimes stereotyped as forbidding talk of unobservables, such as microscopic entities or such notions as causality and general principles, 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.
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 is entities 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, 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, and its doctrines were increasingly criticized, most trenchantly by Willard Van Orman Quine, Norwood Hanson, Karl Popper, Thomas Kuhn, and Carl Hempel.
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. 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.
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 posivists, such as Hans Hahn and Rudolf Carnap. Carnap’s early anti-metaphysical works employed Russell’s theory of types. Carnap envisioned a universal language that could reconstruct mathematics and thereby encode physics. 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. Thus, a universal language failed to stem from Carnap’s 1934 work Logische Syntax der Sprache (Logical Syntax of Language). Still, some logical positivists, including Carl Hempel, continued support of logicism.
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. Starting in the late 19th century, there was a “back to Kant” movement. Ernst Mach’s positivism and phenomenalism were a major influence.
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. 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. 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. As Neurath and somewhat Carnap posed science toward social reform, the split in Vienna Circle also reflected political views