Carnap's theories of confirmation
The first theory of confirmation that Carnap developed in detail is to be found in "Testability and Meaning". In this paper, he addressed the issue of a definition of empiricism, several years after abandoning the quest for a unique and universal logical framework supposed to be the basis of a clear distinction between the meaningful sentences of science and the pseudo-sentences of metaphysics. The principle of tolerance (according to which everyone is free to build up his own form of language as he wishes) had been adopted near the end of 1932, at a time when it was already obvious to Carnap that a strictly verificationist criterion of meaning was inadequate. He therefore considered a variety of empiricisms and a variety of choices for the language of science. As Carnap put it, "there are many different possibilities in framing an empiricist language" and, correspondingly, several degrees of liberalization of the criterion of meaning. It was in this context that Carnap provided both a logical (syntactical) and an empirical analysis of confirmation (and of testing), before distinguishing requirements of different strengths which served the purpose of defining several versions of empiricism.
Wagner, P. (2011)., Carnap's theories of confirmation, in D. Dieks, S. Hartmann, T. Uebel, M. Weber & W. J. González (eds.), Explanation, prediction, and confirmation, Dordrecht, Springer, pp. 477-486.
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