http://dx.doi.org/10.5007/1808-1711.2012v16n1p99 This paper presents a possible but controversial characterization of two periods in Rudolf Carnap’s work: foundationalism and anti-foundationalism. I will argue that even with the identification of two periods, it is possible to argue in favor of the unity of Carnap’s work concerning the unity of science and the principle of linguistic tolerance. To do so, I will count on the analysis of some revisionist views advocated by Friedman and Uebel. Therefore I intend to contribute to a discussion that, (...) since the second half of the twentieth century, seemed to have been overcome, but that, at the end of that century is resumed due to the importance of issues such as the unity of science, observability and interpretation of the scientific language for the philosophy of science. (shrink)