BOOK VI - Page 4

 Kuhn’s Linguistic Analysis of Incommensurability

Philosophers of science such as Feyerabend typically start with linguistic analysis.  But Kuhn was a historian of science, and he firstly wrote his interpretative description in history of science.  Only after many years did he attempt any language analysis to explain and defend his thesis of semantic incommensurability, even though it is a thesis in philosophy of language.  In the years following Structure of Scientific Revolutions his incommensurability thesis evolved considerably, but Kuhn never repudiated it, because it is the keystone for his philosophy of science, without which his metatheory collapses.  It is the keystone that separates and supports his correlative ideas of normal and revolutionary science together with all their philosophical, methodological, and sociological concomitants.  Pull away this keystone and his normal-revolutionary dichotomy would differ only in degree without the discontinuity that incommensurability supplies, thus collapsing his distinctive thesis of scientific revolution. 

Kuhn’s attempts at language analysis expressed in his later papers have been collected and published as a volume titled The Road Since Structure (2000), and in the chapter titled “Afterwords” he states that his efforts to revise and refine his incommensurability thesis have been his primary and increasingly obsessive concern for thirty years, during the last five of which (since 1987) he has made what he calls a rapid series of “significant breakthroughs”. Thus it is in his later papers that his definitive statements are to be found.  But Kuhn seems not to have been comfortable with philosophers’ linguistic analysis.  The knowledgeable reader of Road Since Structure will find himself struggling through Kuhn’s lengthy, laborious, loquacious successive re-inventions of his incommensurability thesis, much as Kuhn himself struggled with language analysis to recast, revise and rescue his semantic incommensurability thesis.

In his autobiographical interview in 1999 he reports that he took the idea of incommensurability from mathematics, where he firstly encountered it in high school while studying calculus and specifically while pondering the proof for the irrationality of the square root of the number two. In another statement of the idea set forth in his “Commensurability, Comparability, Communicability” (1987) reprinted in Road Since Structure he gives other common examples of incommensurability from mathematics: The hypotenuse of an isosceles right triangle is incommensurable with its side; the circumference of a circle is incommensurable with its radius.  He notes that these cases are incommensurable because there is no unit of length contained without residue an integral number of times in each member of the pair.  Mathematicians say these magnitudes have no common integer divisor except the number one.  In mathematics “incommensurability” means there is no common measure, and for his semantic incommensurability Kuhn substitutes “no common language” for “no common measure” for metaphorical use in his Structure of Scientific Revolutions.

Initially in Structure of Scientific Revolutions Kuhn’s discussions of incommensurability were vague.  He reports that he relied on intuition and metaphor, on the double sense – visual and conceptual – of the verb “to see.” In his “Commensurability, Comparability, Communicability” he noted that his view of revolutionary change has been increasingly modified.  He said that his concept of a scientific revolution originated in his discovery that to understand any part of the science of the past, the historian must first learn the language in which it was written, and that the language-learning process is interpretative.  And he maintains that success in interpretation is achieved in large chunks involving the sudden recognition of the new patterns or gestalts, and that the historian experiences revolutions. In the autobiographical interview he noted that in Structure of Scientific Revolutions he had very little to say about meaning change, and instead following Russell Hanson he relied on the idea of gestalt switch, but now (as of the time of the 1999 interview) he says that incommensurability is all language [italics in the editor’s text], and also that it is associated with change of values since values are learned with language.  Early reviewers of Structure of Scientific Revolutions understood Kuhn’s use of “incommensurability” to mean that it is not possible to define any of the terms of one theory into those of the other.  And Kuhn admits that careful reading of Structure of Scientific Revolutions reveals nothing other than this wholistic view, because he explicitly rejected the positivist theory-neutral observation language thesis, and incommensurability strategically precludes any neutral, i.e., theory-independent, observation language. 

But as critics noted in Criticism and the Growth of Knowledge, the wholistic interpretation makes both scientific communication and scientific criticism insolubly problematic.  In response to these criticisms in Criticism and the Growth of Knowledge Kuhn announced his thesis of partial or “local” incommensurability, which enables continuity, comparability, and partial communication between theories outside the area of incommensurability in episodes of revolutionary change.  In the “Postscript” to his “Possible Worlds in History of Science” reprinted in Road Since Structure he explicitly denies in response to a later critic that the change from one theory to another is a discontinuous change, and he says that he has since reformulated his past view which had invoked discontinuity.

Kuhn believes that historians dealing with old scientific texts can and must use modern language to identify the referents of the out-of-date terms.  In “Metaphor in Science” reprinted in Road Since Structure he explained the referential determination that offers continuity with his “causal theory of reference”.  The causal theory of reference denies that proper names have definitions or are associated with definite descriptions.  Instead a proper name is merely a label or a tag, and to identify the individual, one must point it out ostensively, or use some contingent fact about it, or locate its lifeline.  Kuhn extends this theory to naming natural kinds by adding that multiple ostensions (examples) are needed instead of just one, in order to see similarities and contrasts with other individuals.  Illustrating his thesis again in the Copernican revolution he says the techniques of dubbing and of tracing lifelines permit astronomical individuals, e.g., the earth, and the moon, Mars, and Venus, to be traced through episodes of theory change.  The lifelines of these four individuals were continuous, but they were differently distributed among natural families as a result of that change.

Kuhn does not further elaborate the causal theory of reference, and in his autobiographical interview he said that the causal theory of reference does not work for common nouns, but it has some survivals in his philosophy of meaning.  Thus in “Afterwords” he says that one of the characteristics of “kind words” is that they are learned in use by being shown multiple examples of the referent that supply expectations of things and general concepts of properties of the world.  He acknowledges many philosophers maintain that reference is not possible without using concepts to characterize the referent.

Later he further elaborates his theory of referential determination in his “Commensurability, Comparability, and Communicability” reprinted in Road Since Structure, where he distinguishes reference determination from translation.  He says that “no common language” means that there is no language for which either theory in a revolutionary transition can be translated into the other.  While most of the terms common to the successive theories function in the same way for both theories, such that their meanings are preserved and admit to translation, there is a small group of mutually interdefined terms that are incommensurable.  The terms that preserve their meanings across a revolutionary transition provide a sufficient basis for discussions of differences and for comparisons for theory choice.  But he acknowledges that it is not clear that incommensurability can be restricted to a local region of discourse, because the distinction between terms that change meaning and terms that preserve meaning is difficult to explicate. 

He then attempts to evade this problem with his thesis of coreferencing discussed below, but he does not solve it.  In “The Trouble with the Historical Philosophy of Science” reprinted in Road Since Structure he states that the rationality for the scientist’s conclusions requires only that the observations invoked be neutral for or shared by the members of the group making the decision, and for them only at the time the decision is being made.  This thesis offers a neutral language of preserved meanings, which supplies historical continuity and is neutral relative to the time of the revolutionary transition and for the affected scientific group.  But he says that this neutral language is not the same as the positivist observation language, and he rejects the existence of any “Archimedean platform outside space and time”.  In “Afterwords” he states that it is “kind words” that enable identification of referents, things that between their origin and demise have a lifeline through space and time.  “Kind” words constitute the “lexicon” that is strategic to his thesis of incommensurability.

Kuhn offers two reasons for incommensurability. The first reason is stated in his rejection of translatability stated in his “Commensurability, Comparability, Communicability”, where he defines translation as something done by a person who knows two languages, and who systematically substitutes words or strings of words in one language into the other, in order to produce an equivalent text – i.e., salva veritate.  He denies that the two successive theories in a scientific revolution can be translated into one another.  This is obviously true in the sense that the two theories make contrary claims, but Kuhn’s reason is not contrariety but rather incommensurability, and the thrust of his thesis is that one theory cannot even be expressed in the vocabulary of its successor nor vice versa.  Kuhn maintains that the new theory must be “interpreted”, which in his terminology means “learned.”  The interpreter needs to know only one language, and he confronts another language as unintelligible noises and inscriptions.  Quine’s radical translator in Word and Object is not a translator but an interpreter, because successful interpretation is learning a new language.  The interpreter must learn to recognize distinguishing features initially unknown to him, and for which his own language supplies no descriptive terminology.  Thus incommensurability is due to semantics that is unavailable in one language but available in another.

Kuhn attempts to illustrate this kind of incommensurability in the transition from the phlogiston theory of combustion to the modern oxygen theory.  In the phlogiston theory the phrase “dephlogisticated air” can mean either oxygen or oxygen-enriched air, while the phrase “phlogisticated air” means air from which oxygen has been removed.  In the phrase “phlogiston is emitted during combustion”, the term “phlogiston” refers to nothing, although in some cases it refers to hydrogen.  Kuhn maintains that for the historian of science incommensurability in this case is dealt with by learning the meanings in the old texts by reference determination.  He agrees that historians dealing with old scientific texts can and must use modern language to identify referents of out-of-date terms.  Like the native’s pointing out “gavagai” referents in the radical translation situation described by Quine in his Word and Object, such reference determinations may provide concrete examples from which the historian can hope to learn the meanings of problematic expressions in the old texts.  Presumably in the case of “phlogiston” the reference situation is a repetition of the eighteenth-century chemists’ experiments and the comparison of the old language and the modern one describing the observable experimental outcomes. 

But there are some difficulties with this example as described by Kuhn, because he says that translation is impossible since phlogiston is nonexistent, an approach that is nominalist, while Kuhn accepts concepts and rejects nominalism with its purely referential theory of meaning.  The existence of a referent is neither the same as nor a condition for meaningfulness, and Kuhn says that he joins Hesse in maintaining that any extensional theory of meaning is “bankrupt.”  Furthermore translation is not relevant, since the new and old theories express contrary claims and cannot both be true.  But the issue is expressibility, for which both referenceable existence and truth are irrelevant.  The expressibility problem due to incommensurability is that the semantical resources needed for the modern theory are not available in the older one.  Kuhn does not discuss this first reason for incommensurability again after this paper, which was initially delivered at the Philosophy of Science Association annual meeting in 1982.

Kuhn’s second reason is that incommensurability is due to semantical or “lexicon restructuring”.  Kuhn’s initial statement of this reason is found in his “Commensurability, Comparability, Communicability” in the section titled “The Invariants of Translation.”  Here he distinguishes and describes two characteristics of language:

1. Coreferencing.  This means that two users of the same language can employ different criteria for identifying the referents of its descriptive terms.  Coreferencing requires that each user associate each descriptive term with a “cluster of criteria” including contrast sets of terms.  He adds that the sets of terms must be learned together by interpretation, and that this having to learn together is the “holistic” aspect essential to local incommensurability.

2. Structures of criteria.  For each language user a referencing term is a node in a lexical network, from which radiate labels for the criteria he uses in identifying the referents of the nodal term.  Those criteria tie some terms together and at the same time distance them from other terms, thus building a multidimensional structure within the lexicon.  That structure mirrors aspects of the structure of the world, which the lexicon can be used to describe, and it also simultaneously limits the phenomena that can be described with the lexicon.  If anomalous phenomena arise, their description and possibly even their recognition will require altering some part of the language, thus restructuring previously constitutive linkages between terms.

In discussing translation Kuhn says that “homologous” structures mirroring the same world may be fashioned using different sets of criterial linkages.  What such homologous structures preserve is the “taxonomic categories” of the world and the similarity/difference relationships between them.  Different languages impose different structures on the world, and what members of the same language community share is homology of lexical structures, in which the “taxonomic structures” match.  The invariants of translation are matching co-referential expressions and identical lexical structures.  Translation is impossible if taxonomy cannot be preserved, to provide both languages shared categories and relationships.  And when translation is impossible, interpretation, i.e., language acquisition, is required. Finally revolutionary developments in science are those that require taxonomic change, i.e., change in lexical taxonomic structure thus producing incommensurability. 

In his “The “Road Since Structure” also reprinted in Road Since Structure Kuhn states that the “lexical taxonomy” might be called a “conceptual scheme”, which is not a set of beliefs, but rather an “operating mode” of a “mental module” prerequisite to having beliefs, a module that supplies and bonds what is possible to conceive.  He also says that the taxonomic module is prelinguistic and possessed by animals.  In this respect he calls himself a “post-Darwinian Kantian”, because like the Kantian categories the lexicon supplies preconditions of possible experience, while unlike Kantianism the lexicon can and does change.  And he adds that underlying these changes there must be something stable and permanent that is located outside space and time, and like Kant’s Ding an sich is ineffable, inscrutable, and indiscernible.

In “Road Since Structure” and in “Afterwords” Kuhn elaborates further on his idea of lexicon with his thesis of “kind words” or “taxonomic terms”, the vocabulary terms contained in the lexicon.  He states that they have two properties: 1) they are identifiable by their lexical characteristics, notably their occurrence with an indefinite article, and 2) they are subject to Kuhn’s “no-overlap” principle, which is that no two terms with the kind label may overlap in their referents, unless they are related as species to genus, e.g., “male” and “horse” may overlap, but not “horse” and “cow.”

Kuhn illustrates his thesis of taxonomic terms and his principle of no overlap in the language of the Copernican revolution.  He says that the content of the Copernican statement “planets travel around the sun” cannot be expressed in a statement that invokes the celestial taxonomy of the Ptolemaic statement “planets travel around the earth”, and that the difference between the two statements is not simply a matter of fact.  The term “planet” appears in both statements as a kind term, and the two kind terms overlap in membership without either containing all the celestial bodies contained in the other (a genus-species relation), such that there is a change in taxonomic categories that is fundamental.  Kuhn believes that such overlap could not endure, and says that a redistribution of individuals among natural kinds with its consequent alteration of features salient to reference, is the central feature of the episodes he calls revolutions. 

Kind words supply the categories prerequisite to description of and generalization about the world.  Periods in which a speech community deploys overlapping kind words end in one of two outcomes: 1) one meaning entirely displaces the other or 2) the community divides into two groups.  In the resolution of scientific revolutions the former outcome occurs as a result of the crisis phase.  And in the specialization and speciation of new disciplines the latter outcome occurs.  The lexicon of various members of a speech community may vary in the expectations that the lexicons induce, but they must all have the same structure or else mutual incomprehension and breakdown of communication will result.  What is involved in incommensurability – different lexical structure – can only be exhibited ostensively by pointing out examples; it cannot be articulated, i.e., expressed linguistically.

The term “incommensurability” is also central to the philosophy of Paul Feyerabend, and neither he nor Kuhn had claimed priority for its use.  In his autobiographical interview Kuhn claims to have used it independently.  In his “Commensurability, Comparability, Communicability” Kuhn relates his use of the term to Feyerabend’s.  He stated that his use of “incommensurability” was broader than Feyerabend’s, while Feyerabend’s claims are more sweeping.  Kuhn noted that each was led to use the term by problems encountered in interpreting scientific texts, that both were concerned to show that the meanings of scientific terms and concepts such as “force”, “mass”, “element” and “compound”, often changed with changes in the theories that contained them, and that when such theory changes occur it is not possible to define all the terms of one theory into the vocabulary of the other.  In a footnote Kuhn adds that he restricted incommensurability to a few specific terms.  Kuhn said Feyerabend restricted incommensurability to language, while Kuhn initially spoke also of differences in methods, problem-field, and standards of solution.  Later in comparing his views with Feyerabend’s, Kuhn modified his original idea of incommensurability with his thesis of “local incommensurability.”

Kuhn’s Philosophy of Science

Although a historian of science, Kuhn said that he had intended his Structure of Scientific Revolutions for philosophers of science, and that he was disappointed to find that they did not receive it sympathetically. In response to the philosophers he modified and rather awkwardly evolved his philosophy several times over succeeding decades.  But while the sociologists have been smitten with his consensus-conformist criterion, the incommensurability thesis is a semantical thesis, and Kuhn was out of his depth for the linguistic analysis demanded by philosophers.

Of the four basic questions in philosophy of science the most radical aspect of Kuhn’s philosophy is his idea of the aim of science due to his view on scientific criticism and his thesis of semantic incommensurability.  His historical thesis is twofold: In the “normal” science phase the consensus paradigm, which he later identifies with articulate theory, assumes institutional status, such that scientists aim to conform to the consensus view.  Thus conformism is the criterion for scientific criticism, and by ignoring anomalies the empirical criterion is subordinated to this institutionalized criterion of conformism to the prevailing paradigm.  “Scientific progress” therefore is understood as uncritical extension of the consensus paradigm. 

On the other hand in the revolutionary phase, which is an unintended outcome of the conformist-consensus aim of science, semantic incommensurability between old and new successive theories makes the revolutionary transition such that the empirical criterion for theory choice cannot operate.  In response to critics’ questions about the decidability of scientific criticism of revolutionary new theories he later developed his thesis of “local incommensurability”, which permits incommensurable theories to be compared conceptually and empirically by means of the common vocabulary that somehow falls outside of the range of incommensurability. However, within the area of incommensurable vocabulary the language of the new theory must be learned by multiple ostensive demonstrations and/or by approximate paraphrase. 

In response to philosophers’ demand that he supply a linguistic analysis explaining his incommensurability thesis, he had evolved his position substantially over the thirty years following Structure of Scientific Revolutions.  Throughout his life, however, he continued to defend his semantic incommensurability thesis.  He gave two reasons for incommensurability: The first is that the language of the new theory contains descriptive semantics incorporating features of the world not recognized by the earlier preceding theory.  The second is that the contextual determination of the descriptive terms in the statements of a theory results in a restructuring of the semantics of those terms, the “lexicon” of “kind words” i.e., common nouns, when those same terms are carried into the context of the new succeeding theory.

Kuhn says little about the topic of scientific discovery.  He says that he disagrees with Hanson’s thesis that there is a logic for scientific discovery, and Kuhn prefers to speak of the circumstances of discovery.  He makes no comments about the nature of scientific explanation.  Consider next Feyerabend’s philosophy of science and specifically his theses of meaning variance and semantic incommensurability.


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NOTE: Pages do not corresponds with the actual pages from the book