Also known as logical empiricism and scientific empiricism; the ideas and attitude towards philosophy associated with the Vienna circle. This group was founded by Schlick and the mathematician Hans Hahn before the First World War, but entered its most famous period after being reconstituted in 1924. In effect the circle ended with Schlick’s death in 1936 and the dispersal of Austrian intellectuals at that time. Its members included Gustav Bergmann, Rudolf Carnap, Herbert Feigl (1902–88), Otto Neurath, and Friedrich Waismann. Wittgenstein was not a full member of the circle, although closely in touch with its work, maintaining regular meetings with it from 1927 to 1929, and thereafter remaining in contact with Schlick and Waismann. The central interest of the Vienna circle was the unity of science and the correct delineation of scientific method. The idea was that this would act as a final solvent of the disputes of metaphysicians. The task of constructive philosophy became that of analysing the structure of scientific theory and language. The movement can be seen as a development of older empiricist and sensationalist doctrines in the light first of a better understanding of the methodology of empirical science, and secondly of the dramatically increased power of formal logic to permit the definition of abstractions and to describe the structures of permissible inferences. The combination is to some extent foreshadowed in Russell, whose logic and whose concept of a logical construction played a significant role in the doctrines of the movement. The most characteristic doctrine of logical positivism was the verification principle, or denial of literal or cognitive meaning to any statement that is not verifiable: ‘the meaning of a statement is its method of verification.’ The movement gained publicity in the English-speaking world when Ayer published Language, Truth, and Logic in 1936, and maintained some impetus, especially in the philosophy of science, after Carnap and Feigl emigrated to the United States. From 1930 onwards it took over the journal Erkenntnis as the journal of unified science.

Logical positivism retreated under a combination of pressures. First, it shared the traditional problems of radical empiricism, of satisfactorily describing the basis of knowledge in experience (see protocol statements). Secondly, it depended on there being one logic for science, or in other words a confirmation theory with a unique authority, yet no such structure, and certainly no basis for its authority, ever forthcame. These two problems bedevilled accurate formulation of the verification principle, and gradually persuaded philosophers of science that a more holistic and less formal relationship existed between theoretical sentences and the observations supporting them. When this relationship was allowed to be indirect, the despised theses of metaphysics began to look capable of climbing back into respectability. Finally, although logical positivism allowed that science contains statements thought of as logically necessary, its own account of the status of these claims (conventionalism) proved widely unacceptable, and the status of its claims about the basis of meaning in sensation appeared correspondingly doubtful. However, its influence persists in the widespread mistrust of statements for which there are no criteria or assertibility conditions: Wittgenstein’s slogan that meaning is use has frequently been adopted as a rather less forthright invitation to work within the constraints of the principle of verification.