This post is in memory of Prof. Hilary Putnam who died 4 days ago at the age of 89.
Thomas Kuhn’s first edition book, Structure of Scientific Revolutions is a very famous book, and it has caused quite a stir among philosophers of science since its first publication in 1962. Kuhn introduced the idea of a paradigm; a paradigm governs, in the first instance, not a subject matter but rather a group of practitioners. What do members of an isolated community of specialists share that accounts for the relative fullness of their professional communication and the relative unanimity of their professional judgment? To that question, the 1962 Structure licenses the answer, a paradigm or set of paradigms. Scientists would say they share a theory or set of theories.
However, there seemed to be philosophical problems with several themes and concepts in Kuhn’s 1962 work, especially with the “incommensurability thesis”. The thesis of incommensurability of scientific theories is such a controversial thesis in the philosophy of science and it has been criticized and challenged by many philosophers of science since 1962 (the year Kuhn had presented it). The initially heated debate about the concept of a paradigm has considerably cooled down because already in the postscript to the second edition of the Structure Kuhn suggested corrections to his original concept.
In the postscript Kuhn suggests a new term disciplinary matrix: disciplinary because it refers to the common possession of the practitioners of a particular discipline; “matrix” because it is composed of ordered elements of various sorts, each requiring further specification. Kuhn’s 1962 paradigms are constituents of the disciplinary matrix, and as such, they form a whole and function together. “Two groups, the members of which have systematically different sensations on receipt of the same stimuli, do in some sense live in different worlds”. There is no neutral algorithm for theory-choice, no systematic decision procedure which, properly applied, must lead each individual in the group to the same decision. Two men who perceive the same situation differently but nevertheless employ the same vocabulary in its discussion must be using words differently. They speak, that is, from incommensurable viewpoints.
In 1991, Kuhn explained that good reasons for belief could be supplied only by neutral observers, observers which are independent of influences of both beliefs and theories. These provide the stable Archimedean platform required to determine the truth or the probability of the particular belief, law, or theory to be evaluated (judgments). We cannot stand outside the theory and see the world as it is, i.e. compares our theories about the world with reality, the independent world. Only a fixed, rigid Archimedean platform can supply a base from which to measure the distance between current belief and true belief. However, we cannot connect our world of experience to the independent world, because the Archimedean platform outside of history, outside of time and space, is gone beyond recall. Hence, we have no neutral place to stand to evaluate whether or not our statements and propositions correspond to facts that obtain in the independent world.
Critics argued: Kuhn thinks that in order to be in a position to compare theories from older and more recent periods of normal science one needs a perspective external to each and indeed any era of science, but we never are able to escape from our current perspective.
Hilary Putnam argues that human beings are not in a position to judge whether or not our statements correspond to the independent world. To single out a correspondence between two domains, one needs some independent access to both domains. Kuhn talks as if each theory does refer-namely, to its own “world” of entities.
In 1988, in Dubbing and Redubbing Kuhn explained that a historian reading an out-of-date scientific text characteristically encounters passages that make no sense. Kuhn had this experience with Aristotle. It has been standard to ignore such passages or to dismiss them as the products of error, ignorance, or superstition, and that response is occasionally appropriate. Kuhn claims that the troublesome passages result in a different diagnosis. The apparent textual anomalies are artifacts, products of misunderstanding.
The historian has been understanding words and phrases in the text as he or she would if they had occurred in contemporary discourse. Through much of the text that way of reading proceeds without difficulty; most terms in the historian’s vocabulary are still used as they were by the author of the text. But some sets of interrelated terms are not, and it is the failure to isolate those terms and to discover how they were used that has permitted the passages in question to seem anomalous. Apparent anomaly is thus ordinary evidence of the need for local adjustment of the lexicon, and it often provides clues to the nature of the adjustment as well.
In his 1962 Structure Kuhn considered a pair of successive theories in the same historical line, Incommensurability meant that there was no common language into which both could be fully translated. Some statements constitutive of the older theory could not be stated in any language adequate to express its successor and vice versa. Incommensurability thus equals untranslatability, but what incommensurability bars is not quite the activity of professional translators. Kuhn adopts translation of that sort of Quine, Quine’s arguments for indeterminacy of translation: language is not universal. One must give up the assumption that anything expressible in one language, or by using one lexicon, can be expressed also in any other. Meaning must be abandoned. Anything that can be said in one language can, with sufficient imagination and effort, be understood by a speaker of another. What is a prerequisite to such understanding, however, is not a translation but language learning. Quine’s radical translator is, in fact, a language learner. Kuhn is suggesting that the problems of translating a scientific text, whether into a foreign tongue or into a later version of the language in which it was written, are far more like those of translating literature than has generally been supposed. In both cases the translator repeatedly encounters sentences that can be rendered in several alternative ways, none of which captures them completely. The content of alternative theories is unable to be compared due to the meaning variance of the terms employed by the theories. This leads to the reference problem: Different theories seem to employ the same terms to refer to different things. If reference remains stable through variation of conceptual content, no problem of theory comparison arises, since the reference is preserved even though terms may be associated with divergent conceptual content in the context of alternative theories.
Such a refined version of incommensurability was a target for attack. If it is impossible to compare theories either with respect to content or by means of common standards, then it is unclear how a decision between such theories may be made on an objective, rational basis. Such discontinuity in the transition between successive theories (discontinuity in reference), so that no term of a later theory refers to any entity referred to by an earlier theory, conflicts with scientific realism. The realist holds that successive theories in the same domain typically provide alternative descriptions of the same entities and that progress in science consists in an increase in truths known about a common set of entities. But if later theories refer to none of the same entities as earlier theories, then the realist account of scientific progress as an increase of truth about a common set of entities is untenable. The realist holds that the entities to which the terms of a theory refer exist independently of the theory, and that the world investigated by natural science is an objective reality which exists independently of human thought. But such assumption may not be shared by those anti-realist philosophers for whom the objects of reference and the world investigated by science depend in some way on human thought. Some anti-realist philosophers hold that the world and the objects it contains are constituted, either in whole or in part, by our theories, concepts or language. Such philosophers may deny that the terms of conceptually variant theories refer to the same objects since such theories constitute their own domains of reference. Hence, the question of whether later theories refer to the same entities as earlier theories raises metaphysical questions of a kind that tend to divide realism from anti-realism in the philosophy of science.
Critics have attacked Kuhn’s notion of semantic incommensurability. If we do take theories to be potential descriptions of the world, involving reference to worldly entities, kind, and properties, then the problems raised by incommensurability largely evaporate. Critics noted that causal theories of reference permit continuity of reference even through fairly radical theoretical change. Of course, the referentialist response shows only that reference can be retained. Consequently, it is only a partial defense of realism against semantic incommensurability. A further component of the defense of realism against incommensurability must be an epistemic one. For referentialism shows that a term can retain reference and hence that the relevant theories may be such that the later constitutes a better approximation to the truth than the earlier. Nonetheless, it may not be possible for philosophers or others to know that there has been such progress.
Hilary Putnam’s criticism against Kuhn’s semantic incommensurability is embodied in the following notable fable from 1975. Putnam imagines our world has a Doppelgänger twin Earth, a planet just like our own. Let us suppose that somewhere in the galaxy there is a planet which we can call Twin Earth. Twin Earth is very much like Earth. People on Twin Earth speak English. People on Twin Earth who speak English, i.e. the ones who call themselves “Americans”, “Canadians”, “Englishmen” etc. There are a few differences regarding the standard English language on the earth. These differences themselves depend on some of the peculiarities of Twin Earth. One of the differences on Twin Earth compared to the conditions on Earth is that the liquid called “water” is not H2O but a different liquid with a very long and complicated chemical formula abbreviated xyz, indistinguishable from Water H2O at normal temperature and pressure. When Twin Earthians are thirsty they drink xyz. Water xyz tastes like water and it quenches thirst in the same way as Water H2O. The oceans and lakes, rivers and seas of Twin Earth contain water xyz and rain is consisted of the same liquid. The first contact of the Earthians with Twin Earth will produce a report: The word “water” has the same meaning on Earth and on Twin Earth. After the discovery that the liquid called “water” on Twin Earth is not H2O but xyz, the Earthians would correct their description: “On Twin Earth the word ‘water’ means xyz”. Hence the word “water” has two different meanings: on Twin Earth, what we call “water” (consisting of H2O molecules) simply isn’t water.
Let us return to the time when chemistry was not developed on Earth and on Twin Earth. Somewhere about the year 1750. The average Earthian (Oscar) did not know that water consisted of hydrogen and oxygen. The Twin Earthian (Twin-Oscar) did not know that “water” consisted of xyz. Hence, they would conclude that water and “water were the same and in 1750 no one on either Earth or Twin Earth could have distinguished water from “water”. Therefore, if Oscar and Twin-Oscar are not chemically or metallurgically educated, then there may be no difference at all in their psychological state when they use the word water and “water”.
Let us suppose we have a Doppelgänger on Twin Earth who is molecule for molecule identical to me. My Doppelgänger thinks the same verbalized thoughts as I do. In addition, he has the same sense data, the same dispositions, etc. Therefore, I and my Doppelgänger are in the same psychological state: It is absurd to claim that my Doppelgänger’s psychological state is one bit different from mine. My Doppelgänger cannot tell an elm from a beech tree. He means ‘beech’ when he says ‘elm’, and I on Earth mean elm when I say elm. Putnam concludes: “Cut the pie any way you like, “meanings” [that determine the extension of a term] just ain’t in the head! Hence, the psychological state of my Doppelgänger on Twin Earth and of myself on Earth cannot determine the extension (the group of things the term refers to) of any term.
According to Putnam, if we take into account only the individual psychological or cognitive state of Oscar and Twin-Oscar then water refers to “water” for Twin-Oscar. We do not have to rearrange in different ways the term water for Twin-Oscar. From a cognitive point of view, water is being understood by Oscar and Twin-Oscar as the same thing. Kuhn disagreed with Putnam.
Kuhn replied to Putnam: the report the visitors from Earth send home should not be about language but about chemistry. It must take some form like: “back to the drawing board! Something is badly wrong with the chemical theory, and that theory is incompatible with the existence of a substance with properties very nearly the same as water but described by an elaborate chemical formula. Such substance would be too heavy to evaporate at normal terrestrial temperatures. Its discovery and presence would demonstrate the fundamental errors in the chemical theory that gives meanings to compound names like H2O”.
In articles written between the late 1980s and early 1990s, Kuhn offered a new account of incommensurability, which localized meaning change to a restricted class of kind terms. These kind terms, together with their interconnections, form taxonomy that classifies the entities studied in a particular scientific field (taxonomic incommensurability). During a taxonomic change, some kind terms from the old taxonomy are preserved. But at the same time, some new kind terms are added, some old ones are deleted, and many others are rearranged in different ways. Meaning change happens only in a very restricted class of terms and there always exist unchanged concepts that may be used as the basis for rational comparison between rival paradigms. Through the localization of incommensurability, Kuhn hoped to deflect the charge of relativism. In 1993, Ian Hacking related this taxonomy to the world-change thesis: after a revolution, the world of individuals remains as it was, but scientists now work in a world of new kinds.
In 1983 and 1991, Kuhn redrew the picture of scientific revolutions. Changes in taxonomy capture the revolutionary features of paradigm shifts and the most important changes during scientific revolutions can now be conceptualized as taxonomic shifts. The role of taxonomy is not simply linguistic, but also cognitive and psychological. From a cognitive point of view, a taxonomy is a specific structure in the conceptual field defined by a frame. Kuhn sought to distinguish between translating a language (water into “water) and understanding it. Kuhn reasoned that while one might fail to translate from a foreign language into one’s own, it need not follow that one must fail to understand the other language. The combination of these two points yields a refined version of semantic incommensurability, on which translation failure is restricted to specialized vocabularies with a language, which is capable of being understood by rival theories.
Putnam thought that in particular, the individual psychological state of a person does not fix the extension or reference of a term; it is only the sociolinguistic state of the collective linguistic group to which the individual belongs that fixes the extension. Every linguistic community possesses at least some terms that are known only to a subset of the speakers who acquire the terms, and whose use by the other speakers depends upon a structured cooperation between them and the speakers in the relevant subsets.
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