 The celebrated ‘protocol sentence controversy’ in the Vienna Circle was initiated by Carnap’s syntactic analysis of observation sentences, or ‘protocols’ (Carnap 1932a). The salient feature of Carnap’s analysis was its ‘syntacticism’, the idea that meaning is wholly a function of the serial arrangements of symbols. Naturally, syntacticism precludes any effort to explain protocols by their relation to ‘experiences’, ‘sensory impressions’, or ‘observations’. Otto Neurath criticized Carnap’s analysis, arguing that protocols should be understood physicalistically, as sentences of the physical language, and their origins and grounds are to be explicated naturalistically, by means of behaviorist psychology (Uebel 2007, Ch. 8). But Schlick recoiled at the very idea that the relation between observation sentences and what they describe should be explicated by any means other than philosophical analysis. So, in his classic 1934 essay, “On the Foundations of Knowledge,” he introduced so-called ‘affirmations’ (Konstatierungen) in the effort to explicate the relation between physicalistic protocols and the experiences on which they are grounded (Schlick 1979b, 370–387). Otto Neurath responded, in his 1934 essay “Radical Physicalism and the ‘Real World’”, condemning Schlick’s view as just so much metaphysics, while Carnap regarded affirmations as protocols of a phenomenal language, along the lines of one of the alternatives he had outlined in his 1932 paper, “On Protocol Sentences” (Neurath 1983, 66; Carnap 1932b, 458–463). Still, Carnap objected that, unless Schlick could explain how affirmations might be translated into sentences of the physical language, then affirmations violated the thesis of physicalism. Schlick responded that affirmations, like “Here now white”, were the responses of investigators when asked about their personal experiences in experimental situations. Thus construed, the demonstrative character of affirmations ensures their incorrigibility (Schlick 2009, 661–674). Although their demonstrative character prevents them from being regarded as proper physicalistic sentences, they are obviously translatable into statements of the physical language. But then, even though they lose their distinctive epistemic character, for they are no longer incorrigible or indubitable, they still convey epistemic warrant to their physicalistic translations. 