 Foundationalism, in the Cartesian tradition of secure basis, took the beliefs in these terms held by the subject to be infallible, or not requiring verification, as well as the sole empirical source of epistemic warrant—or credibility—for all other beliefs. Descartes’s foundationalism is based on a priori knowledge; Carnap’s presentation of the empirical basis instantiates a more modest version. Still a controversial issue among Carnap scholars, Carnap’s kind of foundationalism would be characterized within one structure as a relation to its basis rather than foundationalism, as in Hume or Descartes, regarding one privileged basis over others. In 1932 Carnap acknowledged that he had adopted a ‘refined form of absolutism of the ur-sentence (“elementary sentence”, “atomic sentence”)’ (1932/1987, 469).