Verificationism
Verificationism, also known as the verification principle or the verifiability criterion of meaning, is a doctrine in philosophy which asserts that a statement is cognitively meaningful only if it is empirically verifiable or an analytic truth. Typically expressed as a criterion of meaning, it rejects traditional statements of metaphysics, theology, ethics and aesthetics as meaningless in terms of conveying truth value or factual content, reducing them to emotive expressions or "pseudostatements" that are neither true nor false.
Verificationism was the central-most thesis of logical positivism, a philosophical movement, in the empiricist tradition, originating in the Vienna Circle and Berlin Circle of the 1920s and 1930s. The logical positivists sought to formulate a scientifically-oriented theory of knowledge in which ambiguities associated with traditional metaphysical language would be negated or minimised, and empirical testability would be enforced as the paradigm of serious inquiry.
Attempts to define a precise criterion of meaning faced intractable problems from the movement's inception. The earliest versions were found to be too restrictive in that they excluded universal generalizations, such as scientific laws. Various alternative proposals were devised, which distinguished between strong and weak verifiability or between practical and in-principle verifiability, and probabilistic variations. In the 1950s, the § theoretical foundations of verificationism encountered escalating scrutiny through the work of philosophers such as Willard Van Orman Quine and Karl Popper. Widespread sentiment deemed it impossible to formulate a universal criterion that could preserve scientific inquiry while rejecting the metaphysical ambiguities the positivists sought to exclude.
By the 1960s, verificationism had become widely regarded as untenable and its abandonment is cited as a decisive factor in the subsequent decline of logical positivism. Nonetheless, it would continue to influence later post-positivist philosophy and empiricist theories of truth and meaning, including the work of philosophers such as Bas van Fraassen, Michael Dummett and Crispin Wright.
Historical background
This section gives the broad historical context in which verificationism was developed and motivated, whereas details on the development of specific aspects of the theory are given in the sections on those aspects.Conceptual origins
Nineteenth- and early twentieth-century empiricism already contained many of the ingredients of verificationism. Pragmatists such as C. S. Peirce and William James linked the meaning of a concept to its practical and experiential consequences, while the conventionalist Pierre Duhem treated physical theories as instruments for organizing observations rather than as literal descriptions of unobservable reality. Later historians have therefore tended to treat verificationism as a sophisticated heir to this broader tradition of empiricist and pragmatist thought. According to Gilbert Ryle, James's pragmatism was "one minor source of the Principle of Verifiability".At the same time, classical empiricism, especially the work of David Hume, provided exemplars for the idea that meaningful discourse must be tied to possible experience, even if Hume himself did not draw the later positivists' radical conclusions about metaphysics. The positivism of Auguste Comte and Ernst Mach reinforced this orientation by insisting that science should confine itself to describing regularities among observable phenomena, a stance that influenced the early logical empiricists' suspicion of unobservable entities and their admiration for the empirical success of theories such as Einstein's general theory of relativity.
The more explicitly semantic side of verificationism drew on developments in analytic philosophy. Ludwig Wittgenstein's Tractatus was read in the 1920s as offering a picture theory of meaning: a proposition is meaningful only insofar as it can represent a possible state of affairs in the world. Members of what would become the Vienna Circle took over this idea in an explicitly empiricist form, treating the "state of affairs" relevant to meaning as something that must in principle be checked in experience.
Logical positivism
By the mid-1920s these strands converged in the programme of logical positivism. Around Moritz Schlick in Vienna, philosophers and scientists such as Rudolf Carnap, Hans Hahn, Philipp Frank and Otto Neurath sought to develop a "scientific philosophy" in which philosophical statements would be as clear, testable and intersubjective as those of the empirical sciences. The "verifiability principle" emerged in this context as a proposed criterion of cognitive meaning, intended to underwrite the movement's anti-metaphysical stance and its aspiration to unify the special sciences within a single, naturalistic framework of knowledge.In Logical Syntax of Language Rudolf Carnap built on earlier work by Gottlob Frege to develop a formal notion of analyticity that defined mathematics and logic as analytic truths, rendering them compatible with verificationism despite their status as non-empirical truths. Outside the German-speaking world, verificationism reached a wider audience above all through A. J. Ayer's Language, Truth and Logic. Drawing on a period of study in Vienna, Ayer presented the verification principle as the central thesis of logical positivism, and his book effectively became a manifesto for the movement in the English-speaking world, even though its specific formulation of the criterion soon came under pressure from critics and from later work by Carnap and others.
Motivation
For members of the Vienna Circle and Berlin Circle, the proposal of a verifiability criterion was attractive for several reasons. By asking, for any disputed sentence, what observations would count for or against it, verificationists hoped to dissolve many traditional philosophical problems as products of linguistic confusion, while preserving, and clarifying, the empirical content of scientific theories. It seemed to offer a precise way of separating genuine questions from pseudo-questions, to explain why many long-standing disputes in metaphysics appeared irresolvable, and to vindicate the special status of the rapidly advancing natural sciences by taking scientific testability as the model for all serious inquiry. The verification principle thus functioned as a kind of intellectual hygiene: sentences that could not, even in principle, be checked against experience were to be diagnosed as cognitively empty rather than as mysteriously profound. The programme appeared to combine respect for the successes of modern science, the new tools of formal logic inspired by Frege and Wittgenstein, and an appealingly deflationary attitude towards grand metaphysical systems.A much-discussed illustration of this attitude is Rudolf Carnap's critique of Martin Heidegger. In his essay "Überwindung der Metaphysik durch logische Analyse der Sprache" Carnap singled out Heidegger's claim that "Nothingness nothings" from the 1929 lecture Was ist Metaphysik? as a paradigm of a metaphysical pseudo-sentence. Although grammatically well-formed, Carnap argued, such a sentence yields no testable consequences and cannot, even in principle, be confirmed or disconfirmed by experience; on a verificationist view it therefore fails to state any fact at all and belongs, at best, to poetry or the expression of mood rather than to cognitive discourse.
Versions of the criterion
Strong verification
According to the verification principle, a declarative sentence is counted as cognitively meaningful only if it is either verifiable by experience or an analytic truth. The principle was typically expressed as a criterion of cognitive meaning or empiricist criterion of cognitive significance, referring to its purpose in demarcating meaningful from meaningless language, ultimately, to exclude "nonsense" while accommodating of the needs of empirical science. The earliest formulations equated cognitive meaning with the need for strong or conclusive verification. In that case, a non-analytic statement is meaningful only if its truth can be logically deduced from a finite set of observation sentences, which report the presence of the observable properties of concrete objects.Members of the Vienna Circle recognised quickly that the requirement for strong verification was too restrictive. Universal generalizations, such as scientific laws, cannot be derived from any finite set of observations so that a strict reading of the principle would render vital domains of empirical science cognitively meaningless. Difficulties also arose on how non-observational language should be reconciled with verificationism. These shortcomings prompted a sustained program to refine the criterion of meaning.
Divisions emerged between "conservative" and "liberal" wings of the Circle regarding the corrective approach. Moritz Schlick and Friedrich Waismann defended a strict verificationism, exploring methods to reinterpret universal statements as rule-like tautologies, so that they would not conflict with the original criterion. Rudolf Carnap, Otto Neurath, Hans Hahn and Philipp Frank advocated a "liberalization of empiricism", proposing that the criterion should be rendered more permissive. Neurath pronounced a physicalist and coherentist approach to scientific language, in which even basic protocol sentences—traditionally considered an infallible experiential foundation—would be subject to revision.
Weak verification and ''empirical import''
's Language, Truth and Logic responded to these difficulties by weakening the requirement on empirical sentences. Ayer distinguished between strong and weak verification, and between practical and in-principle verifiability, allowing a statement to be meaningful so long as experience could in some way count for or against it, even if not conclusively. He later reformulated the criterion in terms of empirical import: a non-analytic sentence has cognitive meaning only if, together with some set of auxiliary premises, it entails an "experiential proposition" that cannot be derived from the auxiliary premises alone. Correspondingly, he distinguished statements that are directly and indirectly verifiable.Carl Hempel and other critics were quick to respond that, unless carefully constrained, Ayer's proposal would trivialise the distinction between meaningful and meaningless statements in that any sentence, or its negation, can be connected with some observational consequences if one is free to introduce auxiliary assumptions. Thus, any "nonsensical" expression can be made meaningful if embedded in a larger sentence that, itself, satisfies the criterion of meaning. In response, Ayer imposed a recursive restriction—allowing only analytic, directly verifiable, or already indirectly verifiable statements as auxiliaries—avoiding outright triviality. However, Hempel argued that it still renders almost any sentence meaningful, allowing for complex sentences that "smuggle in" meaningless expressions.