, Volume 20, Issue 2, pp 373–376

Putting the ‘empiricism’ in ‘logical empiricism’: the director’s cut

Thomas Uebel: Empiricism at the Crossroads: The Vienna Circle’s Protocol-Sentence Debate. Chicago: Open Court Press, 2007, xvii+518 pp, US $89.95 PB


    • Department of PhilosophyHobart and William Smith Colleges
Book Review

DOI: 10.1007/s11016-010-9444-x

Cite this article as:
Frost-Arnold, G. Metascience (2011) 20: 373. doi:10.1007/s11016-010-9444-x

In 1992, Thomas Uebel set the standard for scholarship on both Neurath and the protocol-sentence debate in Overcoming Logical Positivism from Within: The Emergence of Neurath’s Naturalism in the Vienna Circle’s Protocol-Sentence Debate. That book was an in-depth study of the logical empiricists’ protocol-sentence debate, which “concerned the form, content, and status of scientific evidence statements” (1). Put otherwise, this debate addressed how best to understand those scientific activities (including linguistic activities) that make the empirical sciences empirical. The book reviewed here, Empiricism at the Crossroads: The Vienna Circle’s Protocol-Sentence Debate, is a heavily revised and expanded version of that earlier work.

Before delving into the content of the book, let us ask: how does the new version differ from the old? First, there are light revisions throughout, including small expository additions or deletions, and additional citations of primary and secondary sources. Second, there are many entirely new subsections, several of which address developments in the secondary literature since 1992. For example, Uebel engages with Chris Pincock’s ‘reserved reading’ of Carnap’s Aufbau, and when discussing Popper’s interactions with the Vienna Circle, Uebel draws upon Malachi Hacohen’s recent biography. Third, at the macro-level, one old chapter has been deleted (“Beyond Logical Empiricism”), and (roughly) two new chapters have been added. The first covers archival precursors to major articles of the early 1930s (discussed further below), and the second primarily interprets and evaluates Schlick’s puzzling notion of Konstatierungen (‘affirmations’), the supposed evidentiary bedrock of empirical science, including a summary and extension of Uebel’s own recent debate with Thomas Oberdan on this topic.

Despite these many changes great and small, both the general historical narrative and argumentative thrust of Empiricism at the Crossroads are similar to that of the earlier book; Uebel’s fundamental outlook has not undergone radical changes. Many changes involve incorporating further background, or filling in details that were previously omitted. For example, Uebel has increased the space devoted to Carnap, Schlick, and Wittgenstein—Neurath no longer receives the lion’s share of attention.

Let us now turn to more specific content. For those unfamiliar with the 1992 book, a synopsis of Uebel’s project is in order. Although the subtitles of both books refer to the protocol-sentence debate, Uebel’s work is not narrowly focused—far from it. He considers the earlier work of Carnap (especially the Aufbau), Schlick, and Wittgenstein (as well as the Circle’s discussion of it) as antecedents of the protocol-sentence debate. Chapters 2–4 serve as an excellent ‘big picture’ introduction to the state of Logical Empiricism in the late 1920s. Uebel then turns to the protocol-sentence debate proper, providing a ‘slow-motion’ analysis of the debate. Uebel structures the debate into four phases: the first phase is broken into both a right-wing and left-wing camp, the crucial second phase is broken further into three ‘substages,’ each with its own chapter, and the third phase also contains three substages.

For Uebel, the pivotal figure in the debate is (still) Neurath. And the “heart of Neurath’s view of protocol sentences” (411) is an argument against the possibility of a private language (reports of subjective, phenomenal experience) in empirical science. In his Aufbau and afterward, Carnap holds that such a phenomenal (‘solipsist’, ‘autopsychological’) language can play a role in an account of empirical confirmation. (My formulation is intentionally vague, because Carnap’s views change significantly, as Uebel amply shows.) Neurath rejects such phenomenal languages, for the following reason. Suppose yesterday I wrote down what I observed in my laboratory. If I look at that sentence-token in my lab notebook now, to check a hypothesis I formulated today, then I lack first-person, privileged access to the phenomenal consciousness that produced the earlier sentence. Thus, I must treat this sentence the way I would treat another person’s observation report, that is, this sentence is no longer part of my phenomenal language today. Thus, a phenomenal language cannot be used to check hypotheses against observational retrodictions and predictions, and since synchronic observational tests are an essential part of empirical science, a phenomenal language cannot possibly serve as a language for science. Neurath suggests that we should use a “fixed up” version of our everyday language for predictions and observation reports, instead of a phenomenal language (378).

Uebel then considers in detail Popper’s and Schlick’s criticisms of Neurath’s position, Neurathian responses, and how Carnap reacts to all of the above. Uebel deals with many other historical and philosophical issues as well, including whether and to what extent Carnap and Neurath’s apparent differences can be reconciled (short answer: still yes, as in 1992), an interpretation and defense of Neurath’s prima facie puzzling proposal for the correct form of protocol sentences, and (more briefly) how this historical material relates to current philosophical work, e. g. on testimony (Neurath is a local reductionist).

The new material I found most enlightening and fascinating drew upon archival materials that are ancestors of famous publications in the protocol-sentence debate. In particular, Uebel treats at length two early drafts of Carnap’s “Physical Language as the Universal Language of Science” (published in English as The Unity of Science) and “Psychology in Physical Language.” Uebel identifies important changes between the drafts and the final publications and argues convincingly that many of these changes take Carnap closer to Neurath’s views (without complete agreement)—and further from Wittgenstein’s contemporaneous views, primarily as presented to the Circle by Friedrich Waismann. For example, Carnap holds that sentences about the present state of one’s own mind are completely intertranslatable with the physical language, which is the one intersubjective universal language. Previously, Carnap held that phenomenal sentences played a role in verification that could not be filled by the language of observable objects. This brings him closer to Neurath’s views—but they still differ in that Neurath rejects the phenomenal language completely, whereas Carnap does not. What is perhaps most satisfying about these archival materials is that they explain Neurath’s choice of targets in his publications of the early 1930s: the views he attacks are those of Carnap’s earlier unpublished manuscripts (200). That is, if we look only at the published record, Neurath appears to misunderstand or misrepresent his peers; however, he is actually providing arguments against earlier views that were once held, but subsequently changed.

Uebel discusses at length the development of physicalism in Neurath and Carnap. He writes “the ideas of Wittgenstein and their formulation by his emissary Waismann at the beginning of the 1930s, however, constituted an approach that physicalism turned out to be in direct competition with” (169). One might question Uebel’s claim, on the grounds that Wittgenstein claimed that Carnap’s “Psychology in Physical Language” plagiarizes some of Wittgenstein’s ideas, including physicalism (Stern 2007)—since someone who accuses another of plagiarism does not consider their own views to be ‘in direct competition with’ the allegedly plagiarized views. Now, to understand the meaning of Uebel’s claim that the Wittgenstein-Waismann (and later Schlick) camp’s views ‘compete with’ Neurath and Carnap’s physicalism, we need some sense of the meaning of ‘physicalism’ in early 1930s Vienna. Uebel does not explicitly provide a canonical definition, perhaps because the participants’ ideas were in flux. However, Carnap offers the following definition: “physical language is … a language into which every sentence may be translated” (1932/1959, 165). And Neurath, to my knowledge, never provides an explicit definition of ‘physicalism.’

Now, what does Uebel claim are the primary differences between the Wittgenstein-Waismann-Schlick camp, and the Neurath-Carnap one? The former, unlike the latter, hold that there are elementary propositions, which are about phenomena (213), and are unrevisable or un-hypothetical (178, 190). (Actually, Wittgenstein’s views vacillate during this period: in December 1929, he says an epistemically privileged, phenomenal language should be abandoned (86).) However, this is compatible with physicalism, as Carnap defines it: a Carnapian physicalist would only require that these un-hypothetical sentences be translatable into the physical language. So if we understand physicalism according to Carnap’s contemporaneous definition, there is no competition here between the physicalism and the Wittgensteinian camp. However, this Wittgenstein-via-Waismann view is ‘in direct competition’ with what Uebel calls the ‘Neurath principle’, which Carnap shares by 1932 at the latest. This principle finds concrete illumination in Neurath’s parable of the mariner who must rebuild the boat while at sea: even protocol sentences, i.e. observation reports, are hypothetical, and thus the scientific community can revise them. The contradiction here between Wittgenstein-Waismann-Schlick and Neurath-Carnap is clear: the former claim all meaningful statements are hypothetical, i.e. revisable, while the latter deny that claim. However, to repeat, Carnapian physicalism is fully compatible with Wittgenstein-Waismann-Schlick’s denial of the Neurath Principle.

Can we save Uebel’s contention that the two camps clash over physicalism? Here are three possibilities for doing so. First, keep Carnap’s definition above and add the additional premise that these unrevisable, elementary propositions about phenomena cannot be translated into physical language. I know of no texts where Wittgenstein or Waismann articulate this premise; however, Schlick’s Konstatierungen, which Uebel argues are the immediate progeny of the Wittgenstein-Waismann view, do fit the bill. Second, we could replace Carnap’s definition of ‘physicalism’ with one that yields Uebel’s desired conclusion; for example, we could take physicalism to be the denial of the supposed Wittgenstein-Waismann-Schlick claim that every meaningful sentence can be translated or analyzed into elementary sentences in a phenomenal language. Finally, we could define ‘physicalism’ as the denial of the existence or usefulness of a phenomenal language. But which of these three options (if any) Uebel would endorse is not explicit in Empiricism at the Crossroads.

Overall, Empiricism at the Crossroads is a truly impressive achievement. It demonstrates Uebel’s encyclopedic command of primary sources both published and unpublished, and of the full landscape of the burgeoning secondary literature (the 46-page bibliography is a scholarly treasure). Throughout, he makes heavy use of diary entries, letters, and unpublished manuscripts of his protagonists. Uebel’s knowledge of archival material is extraordinary, and I learned an enormous amount about both major and minor figures. For anyone who wishes to learn about the Vienna Circle’s protocol-sentence debate, this book is unquestionably the place to begin. For those already working on the history of logical empiricism, the publication of this new version provides an excellent occasion to revisit Uebel’s erudite treatment of Viennese scientific philosophy.1


I must thank Thomas Uebel for many helpful and insightful discussions regarding some of the material covered in this review.


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© Springer Science+Business Media B.V. 2010