The classical Pragmatists recognized a philosophical significance of the phenomenon of belief.  But belief has taken on a much greater importance in contemporary Pragmatism, where a descriptive discourse believed to be true (what Quine calls the web of beliefs) constitutes a context that controls the semantics of the descriptive terms in the discourse.  This is the contextual or artifactual thesis of the semantics of language.  Thomas Kuhn’s and Paul Feyerabend’s variants of this artifactual thesis of the semantics of language led these two philosophers as well as others to propose new roles for the phenomenon of prejudicial belief in the history and dynamics of scientific development.
           Thomas S. Kuhn (1922-1996) was born in Cincinnati, Ohio.  He received a Bachelor of Science degree summa cum laude from Harvard University in 1943.  His first exposure to history of science came as an assistant to James B. Conant in a course designed to present science to nonscientists.  He received his Ph.D. from Harvard in 1949, and taught history of science at Harvard University, at the University of California at Berkeley (1961), at Princeton University (1964) and at the Massachusetts Institute of Technology (1979). A transcript of an autobiographical interview is reprinted in The Road Since Structure (2000).
          Paul K. Feyerabend (1924-1994) was born in Vienna, Austria.  He was inducted into the Austrian army during World War II, and was wounded in a retreat from the advan­cing Russian army in 1945.  After the war he studied theater at the Wiemar Institute, and then went to the University of Vienna, where he received a Ph.D. in philosophy in 1951.  He then went to England and studied under Popper, whose views he later rejected.  He immigrated to the United States in 1959, and for the remainder of his career taught at University of California at Berkeley.  In 1993 he wrote a brief autobiography titled Killing Time.  The story of the historical approach in twentieth-century philosophy of science, however, begins with Conant.

Conant On Prejudice And The Dynamic View Of Science

          James B. Conant (1883-1978) is the principal influence on the professional thinking of Kuhn.  Kuhn dedicated his popular Structure of Scientific Revolutions to Conant, "Who Started It", and Conant acknowledged Kuhn's contributions to the "Case Histories in Experimental Science" course that Conant started at Harvard University.  Conant received his doctorate in chemistry at Harvard in 1916, and then taught chemistry at Harvard from 1919 to 1933 when he accepted an appointment as the university's president.  In 1953 he resigned his position at Harvard to accept an appointment as U.S. High Commissioner of the Federal Republic of Germany and then later as U.S. Ambassador to Germany.  In 1970 he wrote My Several Lives: Memoirs of A Social Inventor, an autobiography describing the three above-mentioned phases of his profes­sional life.  Conant's views on the history and nature of science are set forth in a series of books.  The earliest is his On Understanding Science: An Historical Approach (1947), which he later expanded into Science And Common Sense (1951).  A year later he published Modern Science And Modern Man (1952), which contains "The Changing Scientific Scene: 1900-1950" in which he elaborates what he calls his skeptical approach to modern quantum theory.  In 1964 he published Two Modes Of Thought, which contains several references to Kuhn's Structure of Scientific Revolutions in context supportive of Kuhn's famous thesis.
          Conant advocates what he calls the dynamic view of science, and he contrasts it with the static view, which he identifies with the Positivist philosophy and specifical­ly with the philosophy set forth by Karl Pearson in the lat­ter's Grammar of Science.  The static view represents science as a systematic body of knowledge, while the dynamic view represents science as an ongoing and continuing activity.  On the dynamic view the present state of knowledge is of importance chiefly as a basis for further research activity.  Conant defines science as an interconnected series of concepts and conceptual schemes that have developed as a result of experimentation, and that are fruitful of further experimentation and observations.  He explicitly rejects the Positivist view that science is a quest for certainty, and he emphasizes that science is a speculative enterprise that is successful only to the degree that it is continuous.
          On his skeptical view microphysical theory does not actually describe reality, but rather is a "policy" that serves as a guide for fruitful future research activity.  He maintains that the wave-particle duality thesis in the quantum theory has changed the attitude of physicists, such that science is now viewed in terms of conceptual schemes, which arise from experiment and are fruitful of more experiments.  The wave-particle duality is one such conceptual scheme, and it justifies his skeptical approach, because this conceptual scheme does not describe what light really is.  Instead modern physics describes the properties of light and formu­lates them on the simplest possible principles.  The history of science is a history of the succession of such conceptual schemes.  Conant references the view of the Harvard Pragmatist philosopher, William James, who maintained that man's intellectual life consists almost wholly in the substitution of a conceptual order for the perceptual order from which experience originally comes.  Different universes of thought arise as concepts and percepts interpenetrate and melt together, impregnate and fertilize each other.  As a result the series of conceptual schemes in the history of science is one in which the conceptual schemes are of increasing adequacy to the perceptions in experimentation.  Conant initially believed that natural sciences have an accumulative character that reveals progress, but following Kuhn's Structure of Scientific Revolu­tions (1962) Conant modified his view of the accumulative nature of science.  He continues to find accumulative progress in the empirical-inductive generalizations in science and also in the practical arts, but he excludes accumulative progress from the theoretical-deductive method, which admits to scientific revolutions.
          Conant identifies the static view with the logical perspective, while he admits the psychological and the sociolo­gical perspectives in his dynamic view.  The sociological perspective reveals that science is a living organization, which can exist due to close communication that enables new ideas to spread rapidly, and that enables discoveries to breed more discoveries.  Scientists pool their information, and by so doing they start a process of cross-fertilization in the realm of ideas.  As a social phenomenon, science is a recent invention starting with the scientific societies of the seventeenth and eighteenth centuries, and then evolving in the universities in the nineteenth century.  Communication was initially through letters, then later through books, and now through journals.  He maintains that historically one of the more important psychological aspects of the development of science is prejudice, a matter toward which he admits he himself has an ambivalent attitude.  On the one hand the traditions of modern science, the instruments, the high degree of specialization, the crowd of witnesses that surround the scientist, all these things exert pressures that make impartiality in matters of science almost automatic.  If the scientist deviates from the rigorous role of impartial experiment or observation, he does so at his peril.  On the other hand Conant says that to put the scientist on a pedestal because he is an impartial inquirer is to misunderstand the historical situation.  This misunderstanding results both from the dogmatic character of textbooks and from the view of Positivist philosophers such as Karl Pearson.  Conant emphasizes the stumbling way in which even the ablest of the scientists of every generation have had to fight through thickets of erroneous observation, misleading generalization, inadequate formulations and unconscious prejudice.  He notes that these problems are rarely appreciated by those who obtain their scientific knowledge from textbooks and by those who expound on the scientific method. 
          Conant exhibits his thesis in his description of the chemical revolution, in which the phlogiston theory of combustion was replaced by the oxygen theory.  He notes that for one hundred fifty years an anomaly to the phlogiston theory, the fact the a calx weighs more than its metal, was known to exist, but that the theory itself was never called into question until a better one was developed to take its place, namely Lavoisier's new conceptual scheme.  In the meanwhile the phlogiston theory was an obstruction to the development of the new conceptual scheme, as scientists attempted to reconcile the anomaly to the phlogiston theory.  Conant also notes that even after the new conceptual scheme was advanced to overthrow the phlogiston scheme, there continued to be debate, and that the proponents of the new conceptual scheme were no more shaken by a few alleged facts contrary to the new scheme, than were the advocates of the old scheme by facts anomalous to the earlier scheme.  Lavoisier pursued his conceptual scheme in spite of embarrassing experimental findings, which only after his death were found to be erroneous findings.  Conant's thesis in this examination of the chemical revolution is that both sides in the controversy had put aside experimental evidence that did not fit into their respective conceptual schemes.  And in his view what is most significant is the frequent fact that subsequent history may show that such arbitrary dismissal of the received truth is quite justified.  He concludes that to suppose that a scientific theory stands or falls on the issue of one experiment is to misunderstand science entirely.  Conant characterizes the first fifty years of the nineteenth century that culminated in the chemists' atomic theory of matter, as a period of the conflict of prejudices.  He notes that one who is not familiar with this episode in the history of science will be amazed to discover that all the relevant ideas and all the basic data for the atomic theory were at hand almost from the outset of the nineteenth century.  An analysis of the arguments, pro and con, shows that certain preconceived ideas then current among scientists blocked its development.  Still, Conant rejects the view that the scientific way of thinking requires the habit of facing reality quite unprejudiced by any earlier conceptions.  In his Science and Common Sense he admits that prejudices are emotional and nonlogical reactions.  Yet he also maintains that every scientist must carry with him the scientific prejudices of his day - the many vague, half-formulated assumptions which to him seem common sense.  Apparently as a result of his acceptance of prejudice as an inevitable fact in the dynamics of science, Conant unabashedly declares that his dynamic view of science is his prejudice, and adds that he makes no attempt to conceal it.
          It may be said that one of the differences between Kuhn and Conant is that the latter regards prejudice as merely an inescapable fact in the history of science, while the former regards it as having a positive function that is inherent in the dynamics of science.  In Kuhn's doctrine of normal science, what Conant calls "prejudice", Kuhn calls by the less pejorative phrase "paradigm consensus".  But unlike Conant, Kuhn does not view prejudice as merely an individual phenomenon with one scientist taking one prejudice and another taking some alternative prejudice.  In Kuhn's view paradigm consensus is a sociological-semantical phenomenon, and this semantical perspective did not come from Conant.  In spite of Conant's dynamic view including reference to William James about percepts being impregnated with concepts, Conant's view of the semantics of language is not dynamic.  His static view of the semantics led him to his skeptical approach, just as it led Bohr to his instrumental view of the formalisms of quantum physics, and for the same reason: without a theory of semantical change, neither Bohr nor Conant could admit a realistic interpretation to the wave-particle duality of the modern quantum theory.  While Conant was a very important influence on Kuhn, Kuhn also has his own formative intellectual experience, which has calls his “Aristotle experience” and which he says is responsible for much that is distinctive and original in his thinking.

Kuhn’s Aristotle Experience

          The twentieth-century philosophers of science who have made influential contributions were inspired by their reflections on the spectacular developments in twentieth-century physics, notably relativity theory and quantum theory.  Kuhn reports that his intellectually formative experience, however, was inspired by his reading Aristotle’s Physics, and he calls this inspiration his Aristotle experience.  His principal account of this experience is published in his “What are Scientific Revolutions?” (1987), and mention is also made in his 1995 autobiographical interview published in Neusis: Journal for the History and Philosophy of Science and Technology (1997), which is also published in an edited version as “A Discussion with Thomas S. Kuhn” in The Road Since Structure (2000) along with a reprint of “What are Scientific Revolutions?”
            Kuhn’s Aristotle experience was occasioned by his reading the physics texts of Aristotle in 1947 as a graduate student in physics at Harvard University in preparation for a case study on the development of mechanics for James B. Conant’s course in science for nonscientists.  Kuhn reports that he approached Aristotle’s texts with the Newtonian mechanics in mind, and that he hoped to answer the question of how much mechanics Aristotle had known and how much he had left for people like Galileo and Newton to discover.  And he states that having brought to the texts the question formulated in that manner, he rapidly discovered that Aristotle had known almost no mechanics at all, and that everything was left for his successors to discover later.  Specifically on the topic of motion Aristotle’s writings seemed to be full of egregious errors, both of logic and of observation.  Kuhn reports that this conclusion was disturbing for him, since Aristotle had been admired as a great logician and was an astute naturalistic observer. 
             Kuhn therefore asked himself whether or not the fault was his rather than Aristotle’s, because Aristotle’s words had not meant to Aristotle and his contemporaries what they mean today to Kuhn and his contemporaries.  Kuhn describes his reconsideration of Aristotle’s Physics: He reports that he continued to puzzle over the text while he was sitting at his desk gazing abstractly out the window of his room with the text of Aristotle’s Physics open before him, when suddenly the fragments in his head sorted themselves out in a new way and fell into place together to present Aristotle as a very good physicist but of a sort that Kuhn had never dreamed possible.  Statements that had previously seemed egregious mistakes afterward seemed at worst near misses within a powerful and generally successful tradition.
            Kuhn then inverts the historical order; his account of scientific revolution describes what Aristotelian natural philosophers required to reach Newtonian ideas instead of what he, a Newtonian reading Aristotle’s text, required to reach those of the Aristotelian natural philosophers.  Thus he maintains that experiences like his Aristotle experience, in which the pieces suddenly sort themselves out and coming together in a new way, is the first general characteristic of revolutionary change in science.  He states that though scientific revolutions leave much mopping up to do, the central change cannot be experienced piecemeal, one step at a time, but that it involves some relatively sudden and unstructured transformation in which some part of the flux of experience sorts itself out differently and displays patterns that had not been visible previously.  Kuhn’s theory of scientific revolutions sparked by his Aristotle experience may be characterized as wholistic (or holistic).  The transition as experienced is synthetic, and Kuhn views it as all of a piece, as it were, denying that it can be understood piecemeal.  In his Structure of Scientific Revolutions he labeled the synthetic character of the revolutionary transitional experience with the phrase “gestalt switch.” But after receiving much criticism from many philosophers of science he eventually attempted a semantical analysis of scientific revolutions. 
            But before Structure of Scientific Revolutions (1962), there was Copernican Revolution, which offers little or no suggestion of his conclusions from his Aristotle experience.  Yet later his examples for semantical analysis routinely come from the Copernican revolution, and seldom come from Aristotle’s texts.

Kuhn on the Copernican Revolution

          Kuhn’s influential and popular Structure of Scientific Revolutions was preceded by his Copernican Revolution: Planetary Astronomy in the Development of Western Thought in 1957.  The earlier work is less philosophical, and it reveals the influence of Conant. The Copernican Revolution contains some ideas that reappear in the Structure of Scientific Revolutions.  One idea is the central feature of scientific revolutions that old theories are replaced by new and incompatible ones.  In the later book this thesis is elaborated in semantical terms, and it is the basis for his describing scientific revolutions as noncumulative episodes in the history of science.  Kuhn says in his autobiographical interview written years later that the noncumulative nature of revolutions was the result of his 1947 Aristotle experience.  However, in the 1957 Copernican Revolution his semantical view is that scientific observations are indifferent to the conceptual schemes that constitute theories, that observations must be distinguished from interpretations of the data that go beyond the data, such that two astronomers can agree perfectly about the results of observation and yet disagree emphatically about issues such as the reality of the apparent motion of the stars.  He states that observations in themselves have no direct consequences for the cosmological theory.  No Positivist would object to these statements.  Later, however, he maintains instead that observations depend on the particular theory held by the scientist, a distinctively post-Positivist thesis.  Thus in his “What are Scientific Revolutions?” (1987) he states that the transition from the Ptolemaic view to the Copernican one involved not only changes in laws of nature as he sees in the development of Boyle’s gas laws, but also involved changes in the criteria by which some terms in the laws attach to nature, i.e. it involved meaning changes, and that the criteria are in part dependent upon the theory containing those terms.  Thus in the Ptolemaic theory the terms “sun” and “moon” refer to planets and “earth” does not, while in the Copernican theory “sun” and “moon” are not referred to as planets and the earth is referred to as a planet like Mars and Jupiter, thereby making the two theories not just incompatible, but what he calls “incommensurable”.  Nonetheless, as he develops his semantical views over the years, he maintains that astronomers holding either theory can pick out the same referents and identify those celestial bodies which are described differently in the two contrary theories.
          A second idea reappearing in the 1962 book is his thesis that the logic of science does not completely control the development of science.  The logic that he has in mind is a stereotype of Popper's view that the occurrence of just one single observation which is incompatible with a theory, dictates that the scientist reject the theory as wrong and abandon it for some other one to replace the wrong one.  Kuhn believes that the incompatibility between theory and observation is the ultimate source for the occurrence of scientific revolutions, but he also maintains that historically the process is never so simple, because scientists do not surrender their beliefs so easily.  What was to Copernicus a stretching and patching to solve the problem of the planets for the two-sphere theory, was to his predecessors a natural process of adaptation and extension.  Kuhn therefore finds in the history of science what he calls "the problem of scientific belief".  That problem is: why do scientists hold to theories despite discrepancies, and then having held to them in these circumstances, why do they later give them up?  The significance that Kuhn gives to this phenomenon reveals the influence of Conant.  The problem of scientific belief is the same as what Conant meant by the phenomenon of prejudice.  Typically historians and philosophers of science did not consider this phenomenon as having any contributing role in the development of science, because it is contrary to the received concept of the aim of science.  And in 1957 Kuhn was clearly as ambivalent in his attitude toward the problem of scientific belief as Conant was toward the phenomenon of prejudice in science.
          In the 1957 book Kuhn locates part of the reason for the problem of scientific belief in the scientist's education, a reason that he also calls "the bandwagon effect".   This reason is carried forward into the 1962 book, where it has a very important place.  In the 1957 book, however, he considers it to be of secondary importance.  The other and more important part of the reason in the 1957 book is the interdependence of other areas of the culture with the scientific specialty.  The astronomer in the time of Copernicus could not upset the two-sphere universe without overturning physics and religion as well.  Fundamental concepts in the pre-Copernican astronomy had become strands for a much larger fabric of thought, and the nonastronomical strands in turn bound the thinking of the astronomers.  The Copernican revolution occurred because Copernicus was a dedicated specialist, who valued mathematical and celestial detail more than the values reinforced by the nonastronomical views that were dependent on the prevailing two-sphere theory.  This purely technical focus of Copernicus enabled him to ignore the nonastronomical consequences of his innovation, consequences which would lead his contemporaries of less restricted vision to reject his innovation as absurd.   In his 1962 book, however, Kuhn does not make the consequences to the nonspecialist an aspect of his general theory of scientific revolutions.  Instead he maintains that scientists persist in their belief in theories with observa­tional discrepancies for reasons that are entirely internal to their specialties.

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