1132913-L

The Moral Philosophy of T.H. Green

It’s been some 25 years since my chum Geoff Thomas’ book was published. It holds the unusual distinction of being one of the very few Phds to be recommended to the OUP committee to publish as a book and it stands the test of time. The recommendation came from none other than Tony Quinton.

Examining Thomas Hill Green’s moral philosophy, Thomas defends a radically new perception of Green as an independent thinker rather than a devoted partisan of Kant or Hegel. Green’s moral philosophy, argues Thomas, includes a widely misunderstood defense of free will, an innovative model of deliberation that rejects both Kantian and Humean conceptions of practical reason, a barely recognized theory of character, and an account of moral objectivity that involves no dependence on religion–all of which yield a coherent body of moral philosophy that raises important problems neglected in contemporary ethics.

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A Note on the Influence of Mach’s Psychology in the Sensory Order

Here are a couple of extracts from Giandomenica Becchio’s paper:

In the Preface of The Sensory Order, Hayek stated that this book was based on his readings in psychology during 1919–1920, when he was still a young student in Vienna interested in both psychology and economics. Among many others, Hayek explicitly cited Mach’s influence on him. Hayek’s contacts with the lively Viennese milieu during the 1920s and 1930s had a fundamental role in the story of the use of Mach in Hayek’s book. As Hayek himself explained, Mach had a great influence on Viennese students and scholars until the 1930s, because he represented ‘‘the only source of arguments against a metaphysical and nebulous attitude’’ that was spreading among scientists (Blackmore, Itagaki, & Tanaka, 2001, p. 124). The use of Mach’s philosophy as a tool against any metaphysical attitude was particularly strong inside the Vienna Circle, where scholars like Otto Neurath and Rudolph Carnap had founded the Ernst Mach Society (Verein Ernst Mach, 1927) to support their movement and to link Mach’s empiricism to their philosophical approach,which they later named ‘‘logical positivism’’ (Blumberg & Feigl, 1931). Hayek strongly criticized the Vienna Circle’s philosophical approach: he mainly rejected Neurath’s physicalism (the belief that all science ultimately reduces to the laws of physics, Neurath, 1931; Caldwell, 2004), even if he showed some interest in Carnap’s logical system (Carnap, 1928). When Hayek introduced the system of multiple classification in The Sensory Order, he cited Carnap as the one who provided ‘‘a somewhat similar statement of the problems of the order of sensory qualities’’ (Hayek, 1952, p. 51). Nevertheless, in the mid-1930s, when Carnap officially subscribed to Neurath’s physicalism, it culminated in the project of the unification of science (Stadler, 2001).1 Hayek’s aversion arose: From the fact that we shall never be able to achieve more than an ‘explanation of the principle’ by which the order of mental events is determined, it also follows that we shall never achieve a complete ‘unification’ of all sciences in the sense that all phenomena of which it treats can be described in physical term. (Hayek, 1952, p. 191)

And in the following footnote he specifically named both Carnap and Neurath: their physical language, since it refers to the phenomenal or sensory qualities of the objects, is not ‘‘physical’’ at all. Their use of this term rather implies a metaphysical belief in the ‘‘ultimate reality’’ and constancy of the phenomenal world for which there is little justification. (ibid.) In this passage Hayek accused them of having dropped their original antimetaphysical attitude – mediated through Mach – to propose a new form a metaphysical belief, based on the reduction of any reality to the empirical realm. Hayek’s j’accuse is significant: for 30 years the philosophers of the Vienna Circle claimed Mach’s philosophy as one of the main sources of their aversion to metaphysics and a pillar of their philosophical approach based on a new form of positivism.2 In the International Encyclopedia of Unified Science, Joergensen explained the three common traits between ‘‘Mach’s positivism’’ and the Vienna Circle philosophy: the idea that ‘‘human knowledge is a biological phenomenon’’; the rejection of any form of ‘‘thing-in-itself’’ (and for that matter, of any form of Kantianism) and the overlap between physical reality and physical elements (Joergensen, 1951, p. 853). To explain the link between Mach and Hayek on the one hand and Hayek’s aversion to the logical positivism (apparently and ‘‘officially’’ rooted in Mach’s philosophy) on the other hand, we need to consider what Hayek meant when he mentioned Mach’s influence in The Sensory Order.

As Hayek himself stated in the Preface of The Sensory Order, psychology is essentially ‘‘dealing with the problems of the methods of the social sciences [a] concern with the logical character of social theory’’ (Hayek, 1952, p. v). From a broader perspective, Hayek’s aversion to reductionism can be seen as the reverse side of the struggle for individualism he started in the late 1930s with the publication of ‘‘Economics and Knowledge’’ and culminated in Individualism and Economic Order (1949), which was published just few years before his decision to revise and finally publish The Sensory Order. During the early 1950s while working on The Sensory Order, Hayek composed ‘‘Within Systems and About Systems,’’ which dealt with the possible knowledge of our mental processes and with the relationship between knowledge and the external environment.

In the early 1930s, Hayek edited Carl Menger’s Collected Works (in German): he also wrote a well-known presentation of Menger’s thought and work. It was published in Economica, and it represented the introduction of Menger to the English-speaking world (Hayek, 1934). In this essay, Hayek stressed the centrality of individualism in Menger’s approach when he had described how markets work and how economic agents behave when they make an economic decision. In the same period Hayek started to work on the link between economic choice and individual knowledge, which culminated in his well-known paper Economics and Knowledge.

From Economics and Knowledge onward, Hayek introduced psychology into economics to explain the dynamics of a society in an individualistic perspective. In this view, Hayek’s decision to work back on revise and publish The Sensory Order can be regarded as the final step of his research project on the nature of individual choice.

After having described the role of knowledge in individual plans and the following mechanism of the market, as well as the use of knowledge in a competition as a discovery process, Hayek described the nature of human mind. The Sensory Order can be seen as Hayek’s tool to show how people know the internal and external reality, how they form their knowledge and how they can share it to make their own plans and coordinate them.

From Hayek’s presentation of Menger’s thought as a stronghold of individualism (1934) to the publication of The Sensory Order (1952), Hayek’s work can be regarded as a tentative to investigate how society works from an individualistic point of view and how the human mind knows from an antireductionist perspective; in opposition to a new kind of holistic and reductionist approach, supported by the predominant position inside the Vienna Circle, mainly by Neurath and Carnap.

The role of Mach in this story is important. Both Hayek and Neurath/Carnap considered Mach the most influential anti-metaphysical thinker. Nevertheless, Neurath/Carnap accepted Mach’s reductionism in psychology as well as his final philosophical approach as a direct development of his psychology. Furthermore, the unity between physics and psychology (between physical and sensorial orders) in Mach’s thought also opened the way to the Vienna Circle’s ideal of a unified science (from physics to social sciences), never accepted by Hayek.

Mach’s influence on Hayek is more complex, though.

Hayek started from Mach’s psychological inquiry, which was influenced by Kant’s research on the nature of knowledge; but, as Mach had refused the final stage of Kantism (the Dich an sich as a metaphysical residuals), Hayek refused the final stage of Machian philosophy (the isomorphism between physical and mental realm as a form of reductionism). Hayek refused Mach’s destruction of ‘‘the conception of elementary and constant sensations as ultimate constituents of the world’’ and he restored ‘‘the necessity of a belief in an objective physical world which is different from that presented to us by our senses’’ (Hayek, 1952, p. 176, 8.37). In a certain sense, Hayek went back to a sort of Kantian dualism, without introducing a negative concept, like Ding an sich. Hayek wrote: The conclusion towhich our theory leads is thus that to us not onlymind as a whole but also all individual mental processes must forever remain phenomena of a special kind, which. Although produced by the same principles which we know to operate in the physical world, we shall never be able fully to explain in terms of physical laws. (Hayek, 1952, p. 191)

It will derive its statements about some mental processes from its knowledge about other mental process, but it will never be able to bridge the gap between the realm of the mental and the realm of the physical. Such a verstehende psychology, which starts from our given knowledge of mental processes, will, however, never be able to explain why we must think thus and not otherwise, why we arrive at particular conclusions (Hayek, 1952, p. 192).

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Hayek’s Post-Positivist Empiricism: Experience Beyond Sensation

Here is Jan Willem Lindemans‘ intro and conclusion to his chapter:

The philosophical foundations of Hayek’s works are not beyond dispute (Caldwell, 1992; Gray, 1984; Hutchison, 1992; Kukathas, 1989): was Hayek a rationalist or an empiricist; did he follow Kant or Hume, Mises or Popper? Difficulties arise because these questions touch upon social theory, political philosophy, methodology, and epistemology. Moreover, on different occasions, Hayek (intentionally) gave different definitions and evaluations of already complicated views such as ‘‘rationalism’’ and ‘‘empiricism.’’

In this chapter, I try to shed some light on the rationalism/empiricism issue by focusing on epistemology, where this issue really belongs. The debate there is mainly about the sources of knowledge (e.g., Markie, 2008). Empiricists argue that experience is the source of all our knowledge. This view was held by John Locke (1632–1704) and David Hume (1711–1776), but its roots go back to Francis Bacon (1561–1626) and even further to the ancient Greek Empiricist school in medicine (founded in the third century B.C. by Philinos of Kos or Serapion of Alexandria) and Aristotle (384–322 B.C.). In contrast with his teacher Plato, Aristotle believed in the ‘‘induction’’ (epago¯ge¯) of general knowledge from particular observations.

I will not have the space here to relate Hayek’s ideas to this long history of empiricism. But I will try to refer to David Hume now and then, because Hayek was a great admirer of Hume’s social and political philosophy and Hayek’s “Humeanism” is extensively discussed. I will also get back to the less well-known Empiricist school in medicine, because it has a very special conception of “experience,” which I believe to be useful to the discussion.

In contrast with empiricism, rationalism or “apriorism” is the idea that some knowledge is independent of experience or “a priori.” Traditionally, this meant that knowledge is based on rational intuition or embedded in our rational nature or the structure of the mind. If knowledge is embedded in our mind or nature, it is “innate,” which is why philosophers speak of “innatism” or ‘‘nativism.’’ Since this was Immanuel Kant’s (1724–1804) view, it is often called ‘‘Kantianism.’’ I will also use the term ‘‘Kantianism’’ rather than ‘‘rationalism’’ because Hayek most often defines the latter as the false view that social phenomena are rationally designed, which is a completely different issue. Kantianism goes back to the ‘‘innate ideas’’ of Rene´ Descartes (1596–1650) and the anamnesis of ideas in Plato’s philosophy (429–347 B.C.).

Many scholars have tried to position Hayek in the Kantianism/empiricism debate. Most scholars would probably agree with Connin (1990, p. 301) that ‘‘Hayek’s theory of knowledge is undoubtedly Kantian’’ (see also Feser, 2006, p. 300).However,many also understand that there is more to it (Caldwell, 2004, p. 273). Since ‘‘experience’’ is undeniably a basic concept in Hayek’s epistemology, some believe that his epistemology is a kind of synthesis between Kantianism and Humean empiricism (Horwitz, 2000, p. 25). De Vecchi (2003, p. 152) is less optimistic and says that ‘‘there is an unresolved tension between empiricism and anti-empiricism within the theory of the process of the formation of knowledge set out in The Sensory Order.’’ Moreover, some have made the link with ‘‘evolutionary epistemology’’ (Bartley, 1987, p. 21;Dempsey, 1996; Gray, 1984; Kukathas, 1989; Vanberg, 2002).

However, scholars have rarely wondered how Kantianism, empiricism, and evolutionism can be reconciled, and, more importantly, what ‘‘empiricism’’ and ‘‘experience’’ mean in such a context. Just as there are as many ‘‘rationalisms’’ as there are interpretations of the term ‘‘reason,’’ there are as many ‘‘empiricisms’’ as there are interpretations of the term ‘‘experience.’’ In this chapter, I will reconstruct Hayek’s epistemology based on a careful reading of The Sensory Order and some related writings. I will argue that Hayek’s epistemology is best characterized as a type of ‘‘post-positivist empiricism.’’

In the first paragraph, I review Hayek’s neurophysiological explanation of the mind in The Sensory Order. Hayek shows how the nervous system can perform the acts of classification characteristic of the working of the mind. Because the synaptic connections embody a kind of knowledge independent of ‘‘sense experience,’’ Hayek is not a ‘‘sensationalist empiricist.’’ The second paragraph discusses Hayek’s theory of the formation of synaptic connections. Connections are formed on the basis of what I will call ‘‘Hayek’s learning rule,’’ which boils down to the familiar idea that neurons that fire together wire together. Since this means that the knowledge embodied in the synaptic connections is in a sense the result of ‘‘experience,’’ be it ‘‘pre-sensory experience’’ rather than ‘‘sense experience,’’ Hayek is an empiricist after all, but one of the ‘‘post-positivist’’ kind. In the third paragraph, I analyze Hayek’s views on the evolution of the nervous system and the behavior it generates. There appear to be two kinds of ‘‘experience’’ Hayek’s Post-Positivist Empiricism: Experience Beyond Sensation at the basis of the synaptic connections: ‘‘experience of the individual’’ and ‘‘experience of the race.’’ Because Hayek denies that all knowledge is due to ‘‘experience of the individual,’’ he is not an ‘‘individualist empiricist.’’ However, since ‘‘experience of the race’’ is also ‘‘experience,’’ he is again an empiricist in the wider sense.

What Hayek failed to notice is that experience of the race is ‘‘postsensory’’ rather than ‘‘pre-sensory’’ and also in other aspects very different from individual experience. I will call it a kind of ‘‘selective experience,’’ which I contrast with ‘‘inductive experience.’’ Some links with Donald Campbell’s ‘‘evolutionary epistemology’’ are explored. In the last paragraph, I consider Campbell’s idea that all increases in knowledge are due to selection and make some suggestions for future research.

Very much like Campbell and Popper, Hayek should be read as an empiricist going beyond traditional empiricism, sensationalism, and positivism: with Hume beyond Hume. Rather than summarizing the whole argument from ‘‘sense experience’’ to ‘‘pre-sensory experience,’’ and from ‘‘individual experience’’ as ‘‘inductive experience’’ to ‘‘racial experience’’ as ‘‘selective experience,’’ I want to end, first, by taking Campbell’s evolutionary epistemology beyond Hayek and, second, by suggesting some possible lines of research. Hayek’s broad empiricism holds that knowledge is based on experience in the wider sense in which it includes individual sense experience, individual pre-sensory experience, and racial experience. However, from an evolutionary epistemological point of view, this empiricism is perhaps too broad.

Evolutionary epistemologists focus on the growth of knowledge and thus the source of increases in knowledge. The ‘‘Basic Selectionist Dogma’’ of Campbell’s ‘‘1960 model’’ (Campbell, 1997, p. 8) states that ‘‘A blindvariation- and-selective-retention process is fundamental to all inductive achievements, to all genuine increases in knowledge, to all increases in fit of system to environment’’ (Campbell, 1960, p. 380). The reason for this radical selectionism is that ‘‘real gains must have been the products of explorations going beyond the limits of foresight or prescience, and in this Learning rule + co-occurring impulses sense blind,’’ since ‘‘if such expansions had represented only wise anticipations, they would have been exploiting full or partial knowledge already achieved’’ (pp. 380–381). This basically means that ‘‘selective experience’’ is the source of all (increases in) knowledge. Hence, ‘‘evolutionary empiricism,’’ though also ‘‘post-positivist,’’ would be much stricter than Hayek’s broad empiricism.

Of course, this does not imply that Hayek’s pre-sensory experience based on the learning rule is nonsense from Campbell’s point of view. The second part of Campbell’s (1960, p. 380) Basic Selectionist Dogma says that ‘‘The many processes which shortcut a more full blind-variation-and-selectiveretention process are in themselves inductive achievements, containing wisdom about the environment achieved originally by blind variation and selective retention.’’ The evolution of Hayek’s learning rule itself is an ‘‘inductive achievement,’’ a ‘‘genuine increase in knowledge.’’ Hayek never reflects much on the fact that the learning rule is itself the result of the ‘‘experience of the race’’ and thus contains knowledge about (the regularity of) the environment. In contrast with the learning rule, the new connections that are the deterministic result of the learning rule are not (completely) ‘‘genuine increases in knowledge’’ since the knowledge was already achieved at the moment the learning rule evolved. Hence, the pre-sensory experience of the individual is still not the most fundamental kind of experience. The ‘‘experience of the race’’ that the learning rule works is a ‘‘pre-pre-sensory experience.’’

The empiricism/rationalism debate is not only about the sources of our beliefs and concepts but also about the justification of our knowledge. It is not only about how people do in fact acquire beliefs about the world but also about how they ought to acquire beliefs. Unfortunately, in The Sensory Order, Hayek was not particularly interested in the question whether knowledge ought to be based on experience. In contrast, Campbell’s evolutionary epistemology is clearly normative. While he sides with the skeptics against traditional epistemologists (Campbell, 1997, p. 12) and holds that ‘‘justification’’ is never complete (p. 13), he does construct a theory of ‘‘justification’’ on the basis of ‘‘Plausible co-selection of belief by referent’’ (p. 9). According to this theory, a belief – or a behavioral disposition other than a belief (cf. supra) – is ‘‘as justified as can be’’ if it is plausible that the belief has been systematically co-selected by the beliefindependent reality to which it refers. For instance, the beliefs we form about objects on the basis of seeing objects are justified if it is plausible that these objects were part of the environment that has selected the eye and the neural system that processes information coming from this eye. Campbell  calls this ‘‘competence of reference’’ selection (p. 10). If there is no such a plausible scenario, or if other co-selectors have probably been more influential, the belief is not justified. Campbell’s idea of co-selection by the belief-independent reality nicely illustrates that ‘‘selective experience’’ must be ‘‘immediate’’ (cf. supra).

Given what has been said, we can redefine ‘‘knowledge’’ as a behavioral disposition that has competence of reference because it was systematically coselected by its referent. Campbell’s theory is an externalist theory of justification because the knower does not necessarily have access to the grounds of justification. Campbell himself relates it to Alvin Goldman’s causal theory of knowledge (p. 9). Indeed, the referent causes the ‘‘belief’’ to survive. More specifically, Campbell’s theory is reliabilist because it claims that ‘‘competence of reference’’ selection processes are reliable sources of truth. Hence, Campbell also relates it to Goldman’s reliabilist theory of justification.

I believe that Campbell’s normative evolutionary epistemology is a welcome complement to Hayek’s epistemological ideas. Refining Hayek’s concept of ‘‘experience’’ and specifying the way in which we can call him an ‘‘empiricist’’ as well as what kind of empiricist he could have been are only the first steps, though. In this chapter, I have restricted the analysis to Hayek’s ‘‘empiricist’’ epistemology, that is, the theory of how people in general (should) acquire knowledge. The next step is to apply this epistemology to two specific classes of individuals, which are very important to Hayek: entrepreneurs and scientists. These are some questions that could be raised: What is the role of ‘‘experience’’ in Hayek’s market economics? Do (or should) entrepreneurs acquire knowledge on the basis of experience? What kind of experience? Can we use the concept of ‘‘selective experience’’ to justify entrepreneurial action? On the other hand, what is the role of ‘‘experience’’ in Hayek’s philosophy of science? Do (or should) scientists – psychologists as well as economists – acquire knowledge on the basis of experience? What kind of experience? Can we use the concept of ‘‘selective experience’’ to justify scientific theories? In that sense, I hope that this chapter is only the beginning.

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Hayek’s Post-Positivist Empiricism: Experience Beyond Sensation

The intro from Jan Willem Lindemans’ paper:

The philosophical foundations of Hayek’s works are not beyond dispute (Gray, 1984, Kukathas, 1989, Caldwell, 1992, Hutchison, 1992): was Hayek a rationalist or an empiricist; did he follow Kant or Hume, Mises or Popper? Difficulties arise because these questions touch upon social theory, political philosophy, methodology and epistemology. Moreover, on different occasions, Hayek (intentionally) gave different definitions and evaluations of already complicated views such as ‘rationalism’ and ‘empiricism’. In this paper, I try to shed some light on the rationalism/empiricism issue by focusing on epistemology, where this issue really belongs. The debate there is mainly about the sources of knowledge (e.g., Markie, 2008). Empiricists argue that experience is the source of all our knowledge. This view was held by John Locke (1632-1704) and David Hume (1711-1776) but its roots go back to Francis Bacon (1561-1626) and even further to the ancient Greek Empiricist school in medicine (founded in the third century B.C. by Philinos of Kos or Serapion of Alexandria) and Aristotle (384-322 B.C.). In contrast with his teacher Plato, Aristotle believed in the ‘induction’ (epagōgē) of general knowledge from particular observations. I will not have the space here to relate Hayek’s ideas to this long history of empiricism. But I will try to refer to David Hume now and then, because Hayek was a great admirer of Hume’s social and political philosophy and Hayek’s ‘Humeanism’ is extensively discussed. I will also get back to the less well known Empiricist school in medicine, because it has a very special conception of ‘experience’ which I believe to be useful to the discussion. In contrast with empiricism, rationalism or ‘apriorism’ is the idea that some knowledge is independent of experience or ‘a priori’. Traditionally, this meant that knowledge is based on rational intuition, or embedded in our rational nature or the structure of the mind. If knowledge is embedded in our mind or nature, it is ‘innate’, which is why philosophers speak of ‘innatism’ or ‘nativism’. Since this was Immanuel Kant’s (1724-1804) view, it is often called ‘Kantianism’. I will also use the term ‘Kantianism’ rather than ‘rationalism’ because Hayek most often defines the latter as the false view that social phenomena are rationally designed, which is a completely different issue. Kantianism goes back to the ‘innate ideas’ of René Descartes (1596-1650) and the anamnesis of ideas in Plato’s philosophy (429-347 B.C.). Many scholars have tried to position Hayek in the Kantianism/empiricism debate. Most scholars would probably agree with Connin (1990, p. 301) that “Hayek’s theory of knowledge is undoubtedly Kantian” (see also Feser, 2006, p. 300). However, many also understand that there is more to it (Caldwell, 2004, p. 273). Since ‘experience’ is undeniably a basic concept in Hayek’s epistemology, some believe that his epistemology is a kind of synthesis between Kantianism and Humean empiricism (Horwitz, 2000, p. 25). De Vecchi (2003, p. 152) is less optimistic and says that “there is an unresolved tension between empiricism and anti-empiricism within the theory of the process of the formation of knowledge set out in The Sensory Order”. Moreover, some have made the link with ‘evolutionary epistemology’ (Bartley, 1987, p. 21; Gray, 1984; Kukathas, 1989; Dempsey, 1996; Vanberg, 2002). However, scholars have rarely wondered how Kantianism, empiricism and evolutionism can be reconciled, and, more importantly, what ‘empiricism’ and ‘experience’ mean in such a context. Just as there are as many ‘rationalisms’ as there are interpretations of the term ‘reason’, there are as many ‘empiricisms’ as there are interpretations of the term ‘experience’. In this paper, I will reconstruct Hayek’s epistemology based on a careful reading of The Sensory Order and some related writings. I will argue that Hayek’s epistemology is best characterized as a type of ‘post-positivist empiricism’. In the first paragraph, I review Hayek’s neurophysiological explanation of the mind in The Sensory Order. Hayek shows how the nervous system can perform the acts of classification characteristic of the working of the mind. Because the synaptic connections embody a kind of knowledge independent of ‘sense experience’, Hayek is not a ‘sensationalist empiricist’. The second paragraph discusses Hayek’s theory of the formation of synaptic connections. Connections are formed on the basis of what I will call ‘Hayek’s learning rule’, which boils down to the familiar idea that neurons that fire together wire together. Since this means that the knowledge embodied in the synaptic connections is in a sense the result of ‘experience’, be it ‘pre-sensory experience’ rather than ‘sense experience’, Hayek is an empiricist after all, but one of the ‘post-positivist’ kind. In the third paragraph, I analyze Hayek’s views on the evolution of the nervous system and the behavior it generates. There appear to be two kinds of ‘experience’ at the basis of the synaptic connections: ‘experience of the individual’ and ‘experience of the race’. Because Hayek denies that all knowledge is due to ‘experience of the individual’, he is not an ‘individualist empiricist’. However, since ‘experience of the race’ is also ‘experience’, he is again an empiricist in the wider sense. What Hayek failed to notice is that experience of the race is ‘post-sensory’ rather than ‘pre-sensory’ and also in other aspects very different from individual experience. I will call it a kind of ‘selective experience’, which I contrast with ‘inductive experience’. Some links with Donald Campbell’s ‘evolutionary epistemology’ are explored. In the last paragraph, I consider Campbell’s idea that all increases in knowledge are due to selection and make some suggestions for future research.

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A Note on the Influence of Mach’s Psychology in the Sensory Order

Here is the intro to Giandomenica Becchio’s paper:

In the Preface of The Sensory Order, Hayek stated that this book was based on his readings in psychology during 1919–1920, when he was still a young student in Vienna interested in both psychology and economics. Among many others, Hayek explicitly cited Mach’s influence on him. Hayek’s contacts with the lively Viennese milieu during the 1920s and 1930s had a fundamental role in the story of the use of Mach in Hayek’s book. As Hayek himself explained, Mach had a great influence on Viennese students and scholars until the 1930s, because he represented ‘‘the only source of arguments against a metaphysical and nebulous attitude’’ that was spreading among scientists (Blackmore, Itagaki, & Tanaka, 2001, p. 124). The use of Mach’s philosophy as a tool against any metaphysical attitude was particularly strong inside the Vienna Circle, where scholars like Otto Neurath and Rudolph Carnap had founded the Ernst Mach Society (Verein Ernst Mach, 1927) to support their movement and to link Mach’s empiricism to their philosophical approach,which they later named ‘‘logical positivism’’ (Blumberg & Feigl, 1931). Hayek strongly criticized the Vienna Circle’s philosophical approach: he mainly rejected Neurath’s physicalism (the belief that all science ultimately reduces to the laws of physics, Neurath, 1931; Caldwell, 2004), even if he showed some interest in Carnap’s logical system (Carnap, 1928). When Hayek introduced the system of multiple classification in The Sensory Order, he cited Carnap as the one who provided ‘‘a somewhat similar statement of the problems of the order of sensory qualities’’ (Hayek, 1952, p. 51). Nevertheless, in the mid-1930s, when Carnap officially subscribed to Neurath’s physicalism, it culminated in the project of the unification of science (Stadler, 2001).1 Hayek’s aversion arose: From the fact that we shall never be able to achieve more than an ‘explanation of the principle’ by which the order of mental events is determined, it also follows that we shall never achieve a complete ‘unification’ of all sciences in the sense that all phenomena of which it treats can be described in physical term. (Hayek, 1952, p. 191)

And in the following footnote he specifically named both Carnap and Neurath: their physical language, since it refers to the phenomenal or sensory qualities of the objects, is not ‘‘physical’’ at all. Their use of this term rather implies a metaphysical belief in the ‘‘ultimate reality’’ and constancy of the phenomenal world for which there is little justification. (ibid.) In this passage Hayek accused them of having dropped their original antimetaphysical attitude – mediated through Mach – to propose a new form a metaphysical belief, based on the reduction of any reality to the empirical realm. Hayek’s j’accuse is significant: for 30 years the philosophers of the Vienna Circle claimed Mach’s philosophy as one of the main sources of their aversion to metaphysics and a pillar of their philosophical approach based on a new form of positivism.2 In the International Encyclopedia of Unified Science, Joergensen explained the three common traits between ‘‘Mach’s positivism’’ and the Vienna Circle philosophy: the idea that ‘‘human knowledge is a biological phenomenon’’; the rejection of any form of ‘‘thing-in-itself’’ (and for that matter, of any form of Kantianism) and the overlap between physical reality and physical elements (Joergensen, 1951, p. 853). To explain the link between Mach and Hayek on the one hand and Hayek’s aversion to the logical positivism (apparently and ‘‘officially’’ rooted in Mach’s philosophy) on the other hand, we need to consider what Hayek meant when he mentioned Mach’s influence in The Sensory Order.