SCHLICK ON THE FOUND A TIO NS OF KNOWLEDGE Risto HILPINEN University of Turku I In the 1930's Moritz Schlick, Rudolf Carnap, Otto Neurath, and other members of the Vienna Circle discussed in the journals Erkenntnis and Analysis problems concerning the criterion of factual truth and the foundation of empirical knowledge. 1 On a superficial analysis, the participants to this discussion can be regarded as representing two main views: Neurath and Carnap seem to accept a version of the coherence theory of truth and knowledge, whereas Schlick seems to be defending a foundationalist account of know­ ledge. In this paper I shall discuss Schlick's foundationalist argu­ ments in detail, and try to show that his view of the empirical basis of knowledge differs in important and interesting respects from the standard foundationalist conception of knowledge. Epistemological foundationalism is usually characterized as a view according to which the system of empirical knowledge (or the system of justified beliefs) has a two-layer structure, and consists of two kinds of beliefs: (i) beliefs which are supported or justified by other beliefs, and (ii) beliefs which support other beliefs, but do not themselves I. Otto Neurath, 'Protokollsatze,' Erkenntnis 3 (1932-33), pp. 204-214; Rudolf Carnap, 'Uber Protokollsatze,' Erkenntnis 3 (1932-33), pp. 215-228; Moritz Schlick, 'Uber das Fundament der Erkenntnis,' Erkenntnis 4 (1934), pp. 79-99; Otto Neurath, 'Radikaler Physikalismus und "Wirkliche Welt,"' Erkenntnis 4 (1934), pp. 346-362; Carl G. Hempel, 'On the Logical Positivists' Theory of Truth,' Analysis 2 (1935), pp. 49-59; Moritz Schlick, 'Facts and Propositions,' Analysis 2 (1935), pp. 65-70; Bela von Juhos, 'Empiricism and Physical ism,' Analysis 2 ( 1935), pp. 81-92; Carl G. Hempel, 'Some Remarks on 'Facts' and Propositions,' Analysis 2 (1935), pp. 93-96. 64 require such support, because they are "self-supporting" or "directly evident" Beliefs of the latter type are said to constitute the foundation or basis of knowledge. This foundation is usually assumed to include, in addition to logical and mathematical truths, propositions which record the immediate experiences of persons without adding any hypothetical content to them, and which are therefore completely free from any uncertainty or doubt and consequently exempt from the requirement of propositional justification. 2 The concept of protocol sentence used by Carnap and Neurath was originally motivated by a foundationalist conception of knowledge: for example, in his paper 'Die physikalische Sprache als Universal­ sprache der Wissenschaft' Carnap takes protocol sentences to be sentences which correspond to "immediately observable states of affairs," and do not require any support from other statements. 3 However, Neurath argued that protocol statements do not have an epistemologically privileged status in t~e system of knowledge, but are subject to revision: empirical knowledge does not possess an in­ corrigible foundation, but every statement, including every observa­ tion statement, can be given up if it turns out to be inconsistent with other propositions in the system. In his paper 'Protokollsatze' Neurath divides the language of science into "protocol sentences" and "non-protocol sentences," but the former are characterized by their form, not by their special epistemic status.4 In the same paper Neurath presents his famous ship metaphor in which he compares the system of knowledge with a ship which the sailors must rebuild in the open sea, without being able to take it to a dry-dock and reconstruct it from new materials. 5 Carnap accepted a similar view: the system of knowledge contains no absolute end-points of justification, and there 2. For a discussion of the main issues concerning foundational theories and coherence theories in epistemology, see Ernest Sosa, 'The Raft and the Pyramid: Coherence versus Foundations in the Theory of Knowledge,' Midwest Studies in Philosophy, Vol. 5 (1980): Studies in Epistemology, ed. by Peter A. French, Theodore E. Uehling, Jr., and Howard K. Wettstein, Minneapolis 1980, pp. 3-25. 3. Erkenntnis 2 (1931-32), pp. 432-465; cf. pp. 437-438. 4. Erkenntnis 3 (1932-33), p. 207. 5. See p. 206. .