III.

Logical Positivists

The name “logical positivists” was attached to a group of philosophers and scientists meeting in Vienna during the 1920s and 1930s. They were influenced by the work of Bertrand Russell, and by the Tractatus Logico-Philosophicus (1921; trans. 1922) of Ludwig Wittgenstein. Chief among them were Moritz Schlick, Rudolph Carnap, Otto Neurath, and Friedrich Waismann, As a young man, A. J. Ayer attended meetings of the Vienna Circle and enthusiastically promulgated their views in his Language, Truth and Logic (1936).

The chief doctrine for which the logical positivists were known was the verification principle, according to which any utterance that could not be confirmed or disconfirmed by experience was rejected as meaningless. Much traditional philosophy and theology was adjudged to fail the test. Truths of logic and mathematics were held to owe their truth to linguistic conventions rather than giving any genuine information about the world.

On the face of it, there are statements that cannot be directly tested by observation, but that are meaningful (for example, talk about electrons). Initially, such statements were granted meaning on the basis of being able to be fully reduced to observational statements. Later, however, the logical positivists took a more relaxed position and held that it was enough if theoretical statements had some observational consequences. Despite placing great importance on observation statements, members of the Vienna Circle disagreed among themselves as to the exact character of these statements. Carnap and Neurath believed that observation statements must refer to physical objects; Schlick and Ayer believed they should refer to sense data.

Although logical positivism was influential for a while, in Britain it gave way to the concerns raised in Wittgenstein’s later philosophy. Criticisms of the verification criterion were not successfully answered. In addition, W. V. O. Quine mounted an influential attack on the analytic-synthetic distinction, which the logical positivists had relied on in their account of logical and mathematical truths.