Twentieth-century philosophical movement that used a strict principle of verifiability to reject as meaningless the non-empirical statements of metaphysics, theology, and ethics. Under the influence of Hume, Russell, and the early Wittgenstein, the logical positivists regarded as meaningful only statements reporting empirical observations, taken together with the tautologies of logic and mathematics. Prominent logical positivists included members of the Vienna Circle and Ayer.
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.