¹ Wittgenstein [1].

² I use this geographical designation because of lack of a suitable name for the movement itself represented by this Circle. It has sometimes been called Logical Positivism, but I am afraid this name suggests too close a dependence upon the older Positivists, especially Comte and Mach. We have indeed been influenced to a considerable degree by the historical positivism, especially in the earlier stage of our development. But today we would like a more general name for our movement, comprehending the groups in other countries which have developed related views (see: Congress [1], [2]). The term ‘Scientific Empiricism’ (proposed by Morris [1] p. 285) is perhaps suitable. In some historical remarks in the following, concerned chiefly with our original group I shall however use the term ‘Vienna Circle’.

³ Schlick [1] p. 150, and [4]; Waismann [1] p. 229.

⁴ Reichenbach [1] and earlier publications; [3].

⁵ Popper [1].

⁶ Lewis [2] has given the most detailed analysis and criticism of the requirement of verifiability.

⁷ Nagel [1].

⁸ Stace [1].

⁹ Schlick [4].

¹⁰ Comp.: Erkenntnis 2, p. 461.

¹¹ Comp.: Carnap [6] p. 32, 34.

¹² Comp.: Carnap [4] §45.—About the indefinite character of the concepts ‘analytic’ and ‘contradictory’ comp.: Carnap [7] p. 163, or: [4b] §34^a and 34^d.

¹³ “Erschüttert,” Neurath [6].

¹⁴ Popper [1].

¹⁵ Lewis [2] p. 137, note 12: “No verification of the kind of knowledge commonly stated in propositions is ever absolutely complete and final.”

¹⁶ Nagel [1] p. 144f.

¹⁷ Reichenbach [1].

¹⁸ Lewis [2] p. 133.

¹⁹ Reichenbach [2] p. 271 ff.; [3] p. 154 ff.

²⁰ Popper [1] Chapter VIII; for the conventional nature of the problem compare my remark in “Erkenntnis” vol. 5, p. 292.

²¹ Lewis [2], especially p. 133.

²² Morris [1], [2].

²³ Here I can give no more than some rough indications concerning the material and the formal idioms. For detailed explanations compare Carnap [4]. Ch. V. A shorter and more easily understandable exposition is contained in [5] p. 85–88.—What I call the formal and the material idioms or modes of speech, is not the same as what Morris ([1], p. 8) calls the formal and the empirical modes of speech. To Morris's empirical mode belong what I call the real object-sentences; and these belong neither to the formal nor to the material mode in my sense (comp. Carnap [4], §74, and [5], p. 61). The distinction between the formal and the material idioms does not concern the usual sentences of science but chiefly those of philosophy, especially those of epistemology or methodology.

²⁴ Lewis [2], p. 127–128.

²⁵ Lewis [2], p. 138.

²⁶ For more exact explanations of these terms see Carnap [4]; some of them are explained also in [5].

²⁷ Compare Hilbert [1] p. 13.

²⁸ In contradistinction to the term ‘atomic sentence’ or ‘elementary sentence’ as used by Russell or Wittgenstein.

²⁹ Carnap [4] §51.

³⁰ Compare Carnap [4] §59.

³¹ Compare Hilbert [1] p. 13; Carnap [4b] §34b, RR 2.

³² Comp. Neurath [1], [2], [3]; Carnap [2], [8].

³³ Compare Carnap [4] §3.