 Bolzano quite clearly faced the problem of how to get from these immediate perceptual judgments, whose objects are completely “private” phenomena which we usually denote by means of indexicals, to an objective description of our world. His epistemology therefore reminds us in many respects of the discussions concerning protocol sentences among the representatives of phenomenalism and physicalism in the Vienna Circle, and even more of Bertrand Russell’s program in his Inquiry into Meaning and Truth (1940). The highly interesting similarities between Bolzano’s and Russell’s program still await further investigation.