A verificationist is someone who adheres to the verification principle proposed by A.J. Ayer in Language, Truth and Logic (1936), a principle and criterion for meaningfulness that requires a non-analytic, meaningful sentence to be empirically verifiable. The term can also, more rarely, refer to a person believing in an altered form, such as the falsification principle. It was hotly disputed amongst verificationists whether the empirical verification itself must be possible in practice or merely in principle, for example, a claim that the world came into existence a short time ago exactly as it is today (with misleading apparent traces of a longer past), would be judged meaningless by a verificationist because it is neither an analytic claim nor a verifiable claim. Ayer distinguished between strong and weak verification.
Strong verification refers to statements which are directly verifiable, that is, a statement can be shown to be correct by way of empirical observation. For example, 'There are human beings on Earth.'
Weak verification refers to statements which are not directly verifiable, for example 'Yesterday was a Monday'. The statement could be said to be weakly verified if empirical observation can render it highly probable.
Historically, the verificationist criterion for meaning had the effect of rendering meaningless many philosophical debates, due to their positing of unverifiable statements or concepts. Notoriously, verificationism has been used to rule out as meaningless religious, metaphysical, and ethical sentences. However, not all verificationists have found sentences of these types to be unverifiable. The classical pragmatists, for example, saw verificationism as a guide for doing good work in religion, metaphysics, and ethics.
All of the empiricists back to Locke could be treated as verificationists. The basic tenet of empiricism is that experience is our only source of knowledge and verificationism might be seen as simply a consequence of this tenet. Empiricists held that our ideas are either simple sense-perceptions or compilations and mixtures of these basic sense-perceptions. Reading this empiricist account, there does not seem to be any way for an idea to get into our heads without being connected to our perceptions and, thus, being connected to a means of verification.
The empiricists did not directly put forth a criterion of meaningfulness, but one could be seen as equivalent to the empiricists' claim that ideas not connected to experience are "empty". It is worth noting, however, that verificationism need not be a position about meaning. It is simply the position that unverifiable sentences are defective in some way that is similar to how false sentences and meaningless sentences are defective. Empiricists could therefore be read as asserting that unverifiable sentences are defective not because they are meaningless, but because they contain terms standing for ideas/concepts that we cannot possibly possess. Or, the empiricist could be read as asserting the semantic position that unverifiable sentences are meaningless precisely because they contain terms standing for ideas/concepts that we cannot possibly possess.
Auguste Comte put forth a semantic position not about the meaninglessness of unverifiable sentences, but rather about the pointlessness of considering them since they cannot be verified. This sort of rejection of unverifiable sentences as useless rather than meaningless would reoccur in the work of the classical pragmatists alongside their semantic verificationism. Comte was a rather extreme verificationist, rejecting everything we cannot have direct experience of. This included statements about the past, universal generalizations, as well as abstract objects like universals.
The verification principle is most associated with the logical positivist movement which had its roots in inter-war Vienna.
Despite pre-dating logical positivism, pragmatism had very little influence on the logical positivists and most attention paid to verificationism has been directed to the positivists. This is mostly because logical positivism, unlike pragmatism, held the possibility of dismissing whole disciplines like metaphysics, morality, and ethics. The pragmatists differed from the logical positivists in their hospitality to areas of knowledge that the positivists hoped their principle would undermine. The pragmatists did not want to rule out metaphysics, religion, or ethics with the verification principle; they wanted to provide a standard for conducting good metaphysics, religion, and ethics.
William James coined the famous verificationist motto: "A difference that makes no difference is no difference".
It is commonly believed that Karl Popper rejected the requirement that meaningful sentences be verifiable, demanding instead that they be falsifiable. However, Popper later claimed that his demand for falsifiability was not meant as a theory of meaning, but rather as a methodological norm for the sciences. Often, and to Popper's dismay, he is grouped as together with the verificationists rather than as a critic of verificationism.
Quine and the Dogmas of Empiricism (1951)
Verificationists need not be logical positivists. Willard Van Orman Quine is a famous example of a verificationist who does not accept logical positivism, on grounds of semantic holism. He suggests that, for theoretical sentences as opposed to observation sentences, meaning is "infected by theory". That theoretical sentences are reducible to observation sentences is one of the ‘dogmas of empiricism’ he rejects as incompatible with semantic holism.
Wittgenstein and the Private Language Argument (1953)
Some interpretations of the Private Language argument see it as a form of verificationism. So for example, Misak claims that:
To say that P is a sentence in a private language is to say that there does not have to be any public consequences if P is true [....] But then 'P seems right to me' will always be a sufficient condition for 'P is right'. There is nothing that would count as evidence for or against the private linguist's claim that she is using a term in the same way or that she is picking out the same property by the term. Nothing would count as evidence to an observer and nothing would count as evidence to the speaker herself.
As we have seen, a crucial part is played in the private-language argument by Wittgenstein's advice 'Always get rid of the idea of the private object in this way: assume that it constantly changes, but that you do not notice the change because your memory constantly deceives you.' This advice has a verificationist ring, and some philosophers have thought that the private-language argument depends, in the last analysis, on verificationist premises. But Wittgenstein's advice is not meant to be followed by the question 'How would you ever find out?' but by the question 'What possible difference would it make?' The private-language argument does indeed depend on premises carried forward from Wittgenstein's earlier philosophy; but they are not peculiar to the verificationist period of the 1930s but date back to the time of the picture theory of the proposition in the 1910s[.]
Bas van Fraassen and Constructive Empiricism (1980)
After the fall of logical positivism, verificationism and empiricism more generally lost many adherents. This trend was stopped and in large part reversed in 1980 with the publication of van Fraassen's The Scientific Image. Constructive empiricism states that scientific theories do not aim at truth, but to be empirically adequate and that their acceptance involves a belief only that they are empirically adequate. A theory is empirically adequate if and only if everything that it says about observable entities is "true" (or well-established). Constructive empiricism therefore rejects unverifiable positions not because they lack truth or meaning, but because they go beyond what is needed to be empirically adequate.
Arthur Fine and the Natural Ontological Attitude (1986)
In 1986, Arthur Fine offered an important alternative to van Fraassen's constructive empiricism with what he decided to playfully entitle the Natural Ontological Attitude (NOA). Fine holds that scientific anti-realists like van Fraassen beg the question against scientific realists when they assume that in theory selection there do not exist reasons to select theories that go beyond what is needed to be empirically adequate. Fine argues that we can avoid this mistake by taking note of what antirealists and realists will both agree to: the reliability of our scientific theories. This recognition of common ground brings Fine to argue that instead of aiming at true scientific theories (as the realist does) or empirically adequate theories (as the constructive empiricist does), we should aim for scientific theories that are reliable for our purposes. Fine's position has an advantage over van Fraassen constructive empiricism in that a NOAer has a ready-made explanation for why there is no reason to select theories that go beyond what is reliable for our purposes; namely, that such theories are irrelevant to our purposes. For this reason Fine is similar to the classical pragmatists from whom he takes inspiration.
It is frequently argued that the verification principle is self-refuting, in that its axioms are neither empirically verifiable nor tautologous.
confirmability in Danish: Verificerbarhedsprincippet
confirmability in German: Verifikationismus
confirmability in Finnish: Verifikationismi
confirmability in Swedish: Verifikationsprincipen