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 :::::::Early critics of logical positivism said that its fundamental tenets could not themselves be formulated consistently. The [[verifiability theory of meaning|verifiability criterion of meaning]] did not seem verifiable; but neither was it simply a logical [[Tautology (logic)|tautology]], since it had implications for the practice of science and the empirical truth of other statements.  This presented severe problems for the logical consistency of the theory.{{cite book |first=H. |last=Putnam |year=1985 |title=Philosophical Papers: Volume 3, Realism and Reason |series=Philosophical Papers |publisher=Cambridge University Press |isbn=9780521313940 |lccn=lc82012903 |url=http://books.google.com/books?id=HAjfSA3ir3kC&pg;=PA184 |page=184}}Another problem was that [[universal quantifier|universal]] claims (""[[all ravens are black]]"") are problematic in terms of verification.{{cite web |first=Thomas |last=Uebel |editor=Edward N. Zalta |year=2008 |title=Vienna Circle |work=The Stanford Encyclopedia of Philosophy |edition=Fall 2008 |url=http://plato.stanford.edu/archives/fall2008/entries/vienna-circle/ |quote=''What Carnap later called the “liberalization of empiricism” was underway and different camps became discernible within the Circle... In the first place,  and the return, as it were, to salient aspects of Carnap's 1928 conception.  Schlick (1931) thus followed Wittgenstein's own suggestion to treat them instead as representing rules for the formation of verifiable singular statements. ( is indicated only in Schlick 1936a.) A second element that began to do so soon was the recognition of the problem of the irreducibility of disposition terms to observation terms... A third element was that disagreement arose as to whether the in-principle verifiability or support turned on what was merely logically possible or on what was nomologically possible, as a matter of physical law etc. A fourth element, finally, was that differences emerged as to whether the criterion of significance was to apply to all languages or whether it was to apply primarily to constructed, formal languages. Schlick retained the focus on logical possibility and natural languages throughout, but Carnap had firmly settled his focus on nomological possibility and constructed languages by the mid-thirties. Concerned with natural language, Schlick (1932, 1936a) deemed all statements meaningful for which it was logically possible to conceive of a procedure of verification; concerned with constructed languages only, Carnap (1936-37) deemed meaningful only statements for whom it was nomologically possible to conceive of a procedure of confirmation of disconfirmation.Many of these issues were openly discussed at the Paris congress in 1935. Already in 1932 Carnap had sought to sharpen his previous criterion by stipulating that those statements were meaningful that were syntactically well-formed and whose non-logical terms were reducible to terms occurring in the basic observational evidence statements of science. {{big|{{red|While Carnap's focus on the reduction of descriptive terms allows for the conclusive verification of some statements, his criterion also allowed universally quantified statements to be meaningful, provided they were syntactically and terminologically correct}}}} (1932a, §2). It was not until one of his Paris addresses, however, that {{big|{{red|Carnap officially declared the meaning criterion to be mere confirmability. Carnap's new criterion required neither verification nor falsification}}}} but only partial testability {{big|{{red|so as now to include not only universal statements}}}} but also the disposition statements of science... Though plausible initially, the device of introducing non-observational terms in this way {{big|{{red|gave rise to a number of difficulties which impugned the supposedly clear distinctions between logical and empirical matters and analytic and synthetic statements}}}} (Hempel 1951). Independently, {{big|{{red|Carnap himself (1939) soon gave up the hope}}}} that all theoretical terms of science could be related to an observational base by such reduction chains. {{big|{{red|This admission raised a serious problem for the formulation of a meaning criterion}}}}''': how was one to rule out unwanted metaphysical claims while admitting as significant highly abstract scienti