## 1. Life and Career


Thomas Kuhn's academic life started in physics. He then switched to
history of science, and as his career developed he moved over to
philosophy of science, although retaining a strong interest in the
history of physics. In 1943, he graduated from Harvard *summa cum
laude*. Thereafter he spent the remainder of the war years in
research related to radar at Harvard and then in Europe. He gained his
master's degree in physics in 1946, and his doctorate in 1949, also in
physics (concerning an application of quantum mechanics to solid state
physics). Kuhn was elected to the prestigious Society of Fellows at
Harvard, another of whose members was W. V. Quine. At this time, and
until 1956, Kuhn taught a class in science for undergraduates in the
humanities, as part of the General Education in Science curriculum,
developed by James B. Conant, the President of Harvard. This course
was centred around historical case studies, and this was Kuhn's first
opportunity to study historical scientific texts in detail. His
initial bewilderment on reading the scientific work of Aristotle was a
formative experience, followed as it was by a more or less sudden
ability to understand Aristotle properly, undistorted by knowledge of
subsequent science. 


 This led Kuhn to concentrate on history of science and in due
course he was appointed to an assistant professorship in general
education and the history of science. During this period his work
focussed on eighteenth century matter theory and the early history of
thermodynamics. Kuhn then turned to the history of astronomy, and in
1957 he published his first book, *The Copernican
Revolution*.


 In 1961 Kuhn became a full professor at the University of
California at Berkeley, having moved there in 1956 to take up a post
in history of science, but in the philosophy department. This enabled
him to develop his interest in the philosophy of science. At Berkeley
Kuhn's colleagues included Stanley Cavell, who introduced Kuhn to the
works of Wittgenstein, and Paul Feyerabend. With Feyerabend Kuhn
discussed a draft of *The Structure of Scientific Revolutions*
which was published in 1962 in the series "International
Encyclopedia of Unified Science", edited by Otto Neurath and
Rudolf Carnap. The central idea of this extraordinarily
influential--and controversial--book is that the development
of science is driven, in normal periods of science, by adherence to
what Kuhn called a 'paradigm'. The functions of a paradigm
are to supply puzzles for scientists to solve and to provide the tools
for their solution. A crisis in science arises when confidence is lost
in the ability of the paradigm to solve particularly worrying puzzles
called 'anomalies'. Crisis is followed by a scientific
revolution if the existing paradigm is superseded by a rival. Kuhn
claimed that science guided by one paradigm would be
'incommensurable' with science developed under a different
paradigm, by which is meant that there is no common measure for
assessing the different scientific theories. This thesis of
incommensurability, developed at the same time by Feyerabend, rules
out certain kinds of comparison of the two theories and consequently
rejects some traditional views of scientific development, such as the
view that later science builds on the knowledge contained within
earlier theories, or the view that later theories are closer
approximations to the truth than earlier theories. Most of Kuhn's
subsequent work in philosophy was spent in articulating and developing
the ideas in *The Structure of Scientific Revolutions*,
although some of these, such as the thesis of incommensurability,
underwent transformation in the process.


According to Kuhn himself (2000, 307), *The Structure of
Scientific Revolutions* first aroused interest among social
scientists, although it did in due course create the interest among
philosophers that Kuhn had intended (and also before long among a much
wider academic and general audience). While acknowledging the
importance of Kuhn's ideas, the philosophical reception was
nonetheless hostile. For example, Dudley Shapere's review (1964)
emphasized the relativist implications of Kuhn's ideas, and this set
the context for much subsequent philosophical discussion. Since the
following of rules (of logic, of scientific method, etc.) was regarded
as the *sine qua non* of rationality, Kuhn's claim that
scientists do not employ rules in reaching their decisions appeared
tantamount to the claim that science is irrational. This was
highlighted by his rejection of the distinction between discovery and
justification (denying that we can distinguish between the
psychological process of thinking up an idea and the logical process
of justifying its claim to truth) and his emphasis on
incommensurability (the claim that certain kinds of comparison between
theories are impossible). The negative response among philosophers was
exacerbated by an important naturalistic tendency in *The Structure
of Scientific Revolutions* that was then unfamiliar. A
particularly significant instance of this was Kuhn's insistence on the
importance of the history of science for philosophy of science. The
opening sentence of the book reads: "History, if viewed as a
repository for more than anecdote or chronology, could produce a
decisive transformation in the image of science by which we are now
possessed" (1962/1970, 1). Also significant and unfamiliar was
Kuhn's appeal to psychological literature and examples (such as
linking theory-change with the changing appearance of a Gestalt
image).


In 1964 Kuhn left Berkeley to take up the position of M. Taylor
Pyne Professor of Philosophy and History of Science at Princeton
University. In the following year an important event took place which
helped promote Kuhn's profile further among philosophers. An
International Colloquium in the Philosophy of Science was held at
Bedford College, London. One of the key events of the Colloquium was
intended to be a debate between Kuhn and Feyerabend, with Feyerabend
promoting the critical rationalism that he shared with Popper. As it
was, Feyerabend was ill and unable to attend, and the papers delivered
focussed on Kuhn's work. John Watkins took Feyerabend's place in a
session chaired by Popper. The ensuing discussion, to which Popper and
also Margaret Masterman and Stephen Toulmin contributed, compared and
contrasted the viewpoints of Kuhn and Popper and thereby helped
illuminate the significance of Kuhn's approach. Papers from these
discussants along with contributions from Feyerabend and Lakatos, were
published several years later, in *Criticism and the Growth of
Knowledge*, edited by Lakatos and Alan Musgrave (1970) (the fourth
volume of proceedings from this Colloquium). In the same year the
second edition of *The Structure of Scientific Revolutions* was
published, including an important postscript in which Kuhn clarified
his notion of paradigm. This was in part in response to Masterman's
(1970) criticism that Kuhn had used 'paradigm' in a wide
variety of ways; in addition, Kuhn felt that critics had failed to
appreciate the emphasis he placed upon the idea of a paradigm as
an *exemplar* or model of puzzle-solving. Kuhn also, for the
first time, explicitly gave his work an anti-realist element by
denying the coherence of the idea that theories could be regarded as
more or less close to the truth.


A collection of Kuhn's essays in the philosophy and history of
science was published in 1977, with the title *The Essential
Tension* taken from one of Kuhn's earliest essays in which he
emphasizes the importance of tradition in science. The following year
saw the publication of his second historical monograph *Black-Body
Theory and the Quantum Discontinuity*, concerning the early
history of quantum mechanics. In 1983 he was named Laurence
S. Rockefeller Professor of Philosophy at MIT. Kuhn continued
throughout the 1980s and 1990s to work on a variety of topics in both
history and philosophy of science, including the development of the
concept of incommensurability, and at the time of his death in 1996 he
was working on a second philosophical monograph dealing with, among
other matters, an evolutionary conception of scientific change and
concept acquisition in developmental psychology.


## 2. The Development of Science


 In *The Structure of Scientific Revolutions* Kuhn paints a
picture of the development of science quite unlike any that had gone
before. Indeed, before Kuhn, there was little by way of a carefully
considered, theoretically explained account of scientific
change. Instead, there was a conception of how science ought to
develop that was a by-product of the prevailing philosophy of science,
as well as a popular, heroic view of scientific progress. According to
such opinions, science develops by the addition of new truths to the
stock of old truths, or the increasing approximation of theories to
the truth, and in the odd case, the correction of past errors. Such
progress might accelerate in the hands of a particularly great
scientist, but progress itself is guaranteed by the scientific
method.


In the 1950s, when Kuhn began his historical studies of science,
the history of science was a young academic discipline. Even so, it
was becoming clear that scientific change was not always as
straightforward as the standard, traditional view would have it. Kuhn
was the first and most important author to articulate a developed
alternative account. Since the standard view dovetailed with the
dominant, positivist-influenced philosophy of science, a non-standard
view would have important consequences for the philosophy of
science. Kuhn had little formal philosophical training but was
nonetheless fully conscious of the significance of his innovation for
philosophy, and indeed he called his work 'history for philosophical
purposes' (Kuhn 2000, 276).


 According to Kuhn the development of a science is not uniform but
has alternating 'normal' and 'revolutionary'
(or 'extraordinary') phases. The revolutionary phases are
not merely periods of accelerated progress, but differ qualitatively
from normal science. Normal science does resemble the standard
cumulative picture of scientific progress, on the surface at
least. Kuhn describes normal science as 'puzzle-solving'
(1962/1970a, 35-42). While this term suggests that normal
science is not dramatic, its main purpose is to convey the idea that
like someone doing a crossword puzzle or a chess problem or a jigsaw,
the puzzle-solver expects to have a reasonable chance of solving the
puzzle, that his doing so will depend mainly on his own ability, and
that the puzzle itself and its methods of solution will have a high
degree of familiarity. A puzzle-solver is not entering completely
uncharted territory. Because its puzzles and their solutions are
familiar and relatively straightforward, normal science can expect to
accumulate a growing stock of puzzle-solutions. Revolutionary science,
however, is not cumulative in that, according to Kuhn, scientific
revolutions involve a revision to existing scientific belief or
practice (1962/1970a, 92). Not all the achievements of the preceding
period of normal science are preserved in a revolution, and indeed a
later period of science may find itself without an explanation for a
phenomenon that in an earlier period was held to be successfully
explained. This feature of scientific revolutions has become known as
'Kuhn-loss' (1962/1970a, 99-100).


 If, as in the standard picture, scientific revolutions are like
normal science but better, then revolutionary science will at all
times be regarded as something positive, to be sought, promoted, and
welcomed. Revolutions are to be sought on Popper's view also, but not
because they add to positive knowledge of the truth of theories but
because they add to the negative knowledge that the relevant theories
are false. Kuhn rejected both the traditional and Popperian views in
this regard. He claims that normal science can succeed in making
progress only if there is a strong commitment by the relevant
scientific community to their shared theoretical beliefs, values,
instruments and techniques, and even metaphysics. This constellation
of shared commitments Kuhn at one point calls a 'disciplinary
matrix' (1970a, 182) although elsewhere he often uses the term
'paradigm'. Because commitment to the disciplinary matrix
is a pre-requisite for successful normal science, an inculcation of
that commitment is a key element in scientific training and in the
formation of the mind-set of a successful scientist. This tension
between the desire for innovation and the necessary conservativeness
of most scientists was the subject of one of Kuhn's first essays in
the theory of science, "The Essential Tension" (1959). The
unusual emphasis on a conservative attitude distinguishes Kuhn not
only from the heroic element of the standard picture but also from
Popper and his depiction of the scientist forever attempting to refute
her most important theories.


 This conservative resistance to the attempted refutation of key
theories means that revolutions are not sought except under
extreme circumstances. Popper's philosophy requires that a single
reproducible, anomalous phenomenon be enough to result in the
rejection of a theory (Popper 1959, 86-7). Kuhn's view is that during
normal science scientists neither test nor seek to confirm the guiding
theories of their disciplinary matrix. Nor do they regard anomalous
results as falsifying those theories. (It is only speculative
puzzle-solutions that can be falsified in a Popperian fashion during
normal science (1970b, 19).) Rather, anomalies are ignored or explained
away if at all possible. It is only the accumulation of particularly
troublesome anomalies that poses a serious problem for the existing
disciplinary matrix. A particularly troublesome anomaly is one that
undermines the practice of normal science. For example, an anomaly
might reveal inadequacies in some commonly used piece of equipment,
perhaps by casting doubt on the underlying theory. If much of normal
science relies upon this piece of equipment, normal science will find
it difficult to continue with confidence until this anomaly is
addressed. A widespread failure in such confidence Kuhn calls a
'crisis' (1962/1970a, 66-76).


 The most interesting response to crisis will be the search for a
revised disciplinary matrix, a revision that will allow for the
elimination of at least the most pressing anomalies and optimally the
solution of many outstanding, unsolved puzzles. Such a revision
will be a scientific revolution. According to Popper the revolutionary
overthrow of a theory is one that is logically required by an
anomaly. According to Kuhn however, there are no rules for deciding
the significance of a puzzle and for weighing puzzles and their
solutions against one another. The decision to opt for a revision of a
disciplinary matrix is not one that is rationally compelled; nor is
the particular choice of revision rationally compelled. For this
reason the revolutionary phase is particularly open to competition
among differing ideas and rational disagreement about their relative
merits. Kuhn does briefly mention that extra-scientific factors might
help decide the outcome of a scientific revolution--the
nationalities and personalities of leading protagonists, for example
(1962/1970a, 152-3). This suggestion grew in the hands of some
sociologists and historians of science into the thesis that the
outcome of a scientific revolution, indeed of any step in the
development of science, is always determined by socio-political
factors. Kuhn himself repudiated such ideas and his work makes it
clear that the factors determining the outcome of a scientific
dispute, particularly in modern science, are almost always to be found
within science, specifically in connexion with the puzzle-solving
power of the competing ideas.


 Kuhn states that science does progress, even through revolutions
(1962/1970a, 160ff). The phenomenon of Kuhn-loss does, in Kuhn's
view, rule out the traditional cumulative picture of progress. The
revolutionary search for a replacement paradigm is driven by the
failure of the existing paradigm to solve certain important
anomalies. Any replacement paradigm had better solve the majority of
those puzzles, or it will not be worth adopting in place of the
existing paradigm. At the same time, even if there is some Kuhn-loss,
a worthy replacement must also retain much of the problem-solving
power of its predecessor (1962/1970a, 169). (Kuhn does clarify the
point by asserting that the newer theory must retain pretty well all
its predecessor's power to solve quantitative problems. It may however
lose some qualitative, explanatory power [1970b, 20].) Hence we can
say that revolutions do bring with them an overall increase in
puzzle-solving power, the number and significance of the puzzles and
anomalies solved by the revised paradigm exceeding the number and
significance of the puzzles-solutions that are no longer available as
a result of Kuhn-loss. Kuhn is quick to deny that there is any
inference from such increases to improved nearness to the truth
((1962/1970a, 170-1). Indeed he later denies that any sense can
be made of the notion of nearness to the truth (1970a, 206).



Rejecting a teleological view of science progressing towards the
truth, Kuhn favours an evolutionary view of scientific progress
(1962/1970a, 170-3), discussed in detail by Wray (2011) (see
also Bird 2000 and Renzi 2009). The evolutionary development of an
organism might be seen as its response to a challenge set by its
environment. But that does not imply that there is some ideal form of
the organism that it is evolving towards. Analogously, science
improves by allowing its theories to evolve in response to puzzles and
progress is measured by its success in solving those puzzles; it is
not measured by its progress towards to an ideal true theory. While
evolution does not lead towards ideal organisms, it does lead to
greater diversity of kinds of organism. As Wray explains, this is the
basis of a Kuhnian account of specialization in science, an account
that Kuhn was developing particularly in the latter part of his
career. According to this account, the revolutionary new theory that
succeeds in replacing another that is subject to crisis, may fail to
satisfy all the needs of those working with the earlier theory. One
response to this might be for the field to develop two theories, with
domains restricted relative to the original theory (one might be the
old theory or a version of it). This formation of new specialties
will also bring with it new taxonomic structures and so leads to
incommensurability.


## 3. The Concept of a Paradigm


A mature science, according to Kuhn, experiences alternating phases
of normal science and revolutions. In normal science the key theories,
instruments, values and metaphysical assumptions that comprise the
disciplinary matrix are kept fixed, permitting the cumulative
generation of puzzle-solutions, whereas in a scientific revolution the
disciplinary matrix undergoes revision, in order to permit the
solution of the more serious anomalous puzzles that disturbed the
preceding period of normal science.


A particularly important part of Kuhn's thesis in *The Structure
of Scientific Revolutions* focuses upon one specific component of
the disciplinary matrix. This is the consensus on exemplary instances
of scientific research. These exemplars of good science are what Kuhn
refers to when he uses the term 'paradigm' in a narrower
sense. He cites Aristotle's analysis of motion, Ptolemy's
computations of plantery positions, Lavoisier's application of the
balance, and Maxwell's mathematization of the electromagnetic field as
paradigms (1962/1970a, 23). Exemplary instances of science are
typically to be found in books and papers, and so Kuhn often also
describes great texts as paradigms--Ptolemy's *Almagest*,
Lavoisier's *Traite elementaire de
chimie*, and Newton's *Principia Mathematica* and
*Opticks* (1962/1970a, 12). Such texts contain not only the
key theories and laws, but also--and this is what makes them
paradigms--the applications of those theories in the solution of
important problems, along with the new experimental or mathematical
techniques (such as the chemical balance in *Traite
elementaire de chimie* and the calculus in
*Principia Mathematica*) employed in those applications.


In the postscript to the second edition of *The Structure of
Scientific Revolutions* Kuhn says of paradigms in this sense that
they are "the most novel and least understood aspect of this
book" (1962/1970a, 187). The claim that the consensus of a
disciplinary matrix is primarily agreement on paradigms-as-exemplars
is intended to explain the nature of normal science and the process of
crisis, revolution, and renewal of normal science. It also explains
the birth of a mature science. Kuhn describes an immature science, in
what he sometimes calls its 'pre-paradigm' period, as
lacking consensus. Competing schools of thought possess differing
procedures, theories, even metaphysical presuppositions. Consequently
there is little opportunity for collective progress. Even localized
progress by a particular school is made difficult, since much
intellectual energy is put into arguing over the fundamentals with
other schools instead of developing a research tradition. However,
progress is not impossible, and one school may make a breakthrough
whereby the shared problems of the competing schools are solved in a
particularly impressive fashion. This success draws away adherents
from the other schools, and a widespread consensus is formed around
the new puzzle-solutions.


This widespread consensus now permits agreement on
fundamentals. For a problem-solution will embody particular theories,
procedures and instrumentation, scientific language, metaphysics, and
so forth. Consensus on the puzzle-solution will thus bring consensus
on these other aspects of a disciplinary matrix also. The successful
puzzle-solution, now a paradigm puzzle-solution, will not solve all
problems. Indeed, it will probably raise new puzzles. For example, the
theories it employs may involve a constant whose value is not known
with precision; the paradigm puzzle-solution may employ approximations
that could be improved; it may suggest other puzzles of the same kind;
it may suggest new areas for investigation. Generating new puzzles is
one thing that the paradigm puzzle-solution does; helping solve them
is another. In the most favourable scenario, the new puzzles raised by the paradigm
puzzle-solution can be addressed and answered using precisely the
techniques that the paradigm puzzle-solution employs. And since the
paradigm puzzle-solution is accepted as a great achievement, these
very similar puzzle-solutions will be accepted as successful solutions
also. This is why Kuhn uses the terms 'exemplar' and
'paradigm'. For the novel puzzle-solution which
crystallizes consensus is regarded and used as a model of exemplary
science. In the research tradition it inaugurates, a
paradigm-as-exemplar fulfils three functions: (i) it suggests new
puzzles; (ii) it suggests approaches to solving those puzzles; (iii)
it is the standard by which the quality of a proposed puzzle-solution
can be measured (1962/1970a, 38-9). In each case it is similarity to
the exemplar that is the scientists' guide.


That normal science proceeds on the basis of perceived similarity
to exemplars is an important and distinctive feature of Kuhn's new
picture of scientific development. The standard view explained the
cumulative addition of new knowledge in terms of the application of
the scientific method. Allegedly, the scientific method encapsulates
the rules of scientific rationality. It may be that those rules could
not account for the creative side of science--the generation of
new hypotheses. The latter was thus designated 'the context of
discovery', leaving the rules of rationality to decide in the
'context of justification' whether a new hypothesis should,
in the light of the evidence, be added to the stock of accepted
theories. 


Kuhn rejected the distinction between the context of discovery and
the context of justification (1962/1970a, 8), and correspondingly
rejected the standard account of each. As regards the context of
discovery, the standard view held that the philosophy of science had
nothing to say on the issue of the functioning of the creative
imagination. But Kuhn's paradigms do provide a partial explanation,
since training with exemplars enables scientists to see new
puzzle-situations in terms of familiar puzzles and hence enables them
to see potential solutions to their new puzzles. 


More important for Kuhn was the way his account of the context of
justification diverged from the standard picture. The functioning of
exemplars is intended explicitly to contrast with the operation of
rules. The key determinant in the acceptability of a proposed
puzzle-solution is its similarity to the paradigmatic
puzzle-solutions. Perception of similarity cannot be reduced to rules,
and a fortiori cannot be reduced to rules of rationality. This
rejection of rules of rationality was one of the factors that led
Kuhn's critics to accuse him of irrationalism--regarding science
as irrational. In this respect at least the accusation is wide of the
mark. For to deny that some cognitive process is the outcome of
applying rules of rationality is not to imply that it is an irrational
process: the perception of similarity in appearance between two
members of the same family also cannot be reduced to the application
of rules of rationality. Kuhn's innovation in *The Structure of
Scientific Revolutions* was to suggest that a key element in
cognition in science operates in the same fashion.


## 4. Incommensurability and World-Change


The standard empiricist conception of theory evaluation regards our
judgment of the epistemic quality of a theory to be a matter of
applying rules of method to the theory and the evidence. Kuhn's
contrasting view is that we judge the quality of a theory (and its
treatment of the evidence) by comparing it to a paradigmatic
theory. The standards of assessment therefore are not permanent,
theory-independent rules. They are not rules, because they involve
perceived relations of similarity (of puzzle-solution to a
paradigm). They are not theory-independent, since they involve
comparison to a (paradigm) theory. They are not permanent, since the
paradigm may change in a scientific revolution. For example, to many
in the seventeenth century, Newton's account of gravitation, involving
action at a distance with no underlying explanation, seemed a poor
account, in that respect at least, when compared, for example, to
Ptolemy's explanation of the motion of the planets in terms of
contiguous crystalline spheres or to Descartes' explanation in
terms of vortices. However, later, once Newton's theory had become
accepted and the paradigm by which later theories were judged, the lack
of an underlying mechanism for a fundamental force was regarded as no
objection, as, for example, in the case of Coulomb's law of
electrostatic attraction. Indeed, in the latter case the very
similarity of Coulomb's equation to Newton's was taken to be in its
favour.


Consequently, comparison between theories will not be as
straightforward as the standard empiricist picture would have it,
since the standards of evaluation are themselves subject to
change. This sort of difficulty in theory comparison is an instance of
what Kuhn and Feyerabend called
'incommensurability'. Theories are incommensurable when
they share no common measure. Thus, if paradigms are the measures of
attempted puzzle-solutions, then puzzle-solutions developed in
different eras of normal science will be judged by comparison to
differing paradigms and so lack a common measure. The term
'incommensurable' derives from a mathematical use,
according to which the side and diagonal of a square are
incommensurable in virtue of there being no unit that can be used to
measure both exactly. Kuhn stressed that incommensurability did not
*mean* non-comparability (just as the side and diagonal of a
square are comparable in many respects). Even so, it is clear that at
the very least Kuhn's incommensurability thesis would make theory
comparison rather more difficult than had commonly been supposed, and
in some cases impossible.


We can distinguish three types of incommensurability in Kuhn's
remarks: (1) methodological--there is no common measure because
the methods of comparison and evaluation change; (2)
perceptual/observational--observational evidence cannot provide a
common basis for theory comparison, since perceptual experience is
theory-dependent; (3) semantic--the fact that the languages of
theories from different periods of normal science may not be
inter-translatable presents an obstacle to the comparison of those
theories. (See Sankey 1993 for a useful discussion of Kuhn's changing
accounts of incommensurability.)


### 4.1 Methodological Incommensurability


The incommensurability illustrated above whereby puzzle-solutions
from different eras of normal science are evaluated by reference to
different paradigms, is methodological incommensurability. Another
source of methodological incommensurability is the fact that
proponents of competing paradigms may not agree on which problems a
candidate paradigm should solve (1962/1970a, 148). In general the
factors that determine our choices of theory (whether puzzle-solutions
or potential paradigm theories) are not fixed and neutral but vary and
are dependent in particular on the disciplinary matrix within which
the scientist is working. Indeed, since decision making is not
rule-governed or algorithmic, there is no guarantee that those working
within the same disciplinary matrix must agree on their evaluation of
theory (1962/1970a, 200), although in such cases the room for
divergence will be less than when the disputants operate within
different disciplinary matrices. Despite the possibility of
divergence, there is nonetheless widespread agreement on the desirable
features of a new puzzle-solution or theory. Kuhn (1977, 321-2)
identifies five characteristics that provide *the* shared basis
for a choice of theory: 1. accuracy; 2. consistency (both internal and
with other relevant currently accepted theories); 3. scope (its
consequences should extend beyond the data it is required to explain);
4. simplicity (organizing otherwise confused and isolated phenomena);
5. fruitfulness (for further research). Even though these are, for
Kuhn, constitutive of science (1977c, 331; 1993, 338) they cannot
determine scientific choice. First, which features of a theory satisfy
these criteria may be disputable (e.g. does simplicity concern the
ontological commitments of a theory or its mathematical
form?). Secondly, these criteria are imprecise, and so there is room
for disagreement about the degree to which they hold. Thirdly, there
can be disagreement about how they are to be weighted relative to one
another, especially when they conflict.


### 4.2 Perception, Observational Incommensurability, and World-Change


An important focus of Kuhn's interest in *The Structure of
Scientific Revolutions* was on the nature of perception and how it
may be that what a scientist observes can change as a result of
scientific revolution. He developed what has become known as the
thesis of the theory-dependence of observation, building on the work
of N. R. Hanson (1958) while also referring to psychological studies
carried out by his Harvard colleagues, Leo Postman and Jerome Bruner
(Bruner and Postman 1949). The standard positivist view was that
observation provides the neutral arbiter between competing
theories. The thesis that Kuhn and Hanson promoted denied this,
holding that the nature of observation may be influenced by prior
beliefs and experiences. Consequently it cannot be expected that two
scientists when observing the same scene will make the same
theory-neutral observations. Kuhn asserts that Galileo and an
Aristotelian when both looking at a pendulum will see different things
(see quoted passage below).


The theory-dependence of observation, by rejecting the role of
observation as a theory-neutral arbiter among theories, provides
another source of incommensurability. Methodological
incommensurability (SS4.1 above) denies that there are universal
methods for making inferences from the data. The theory-dependence of
observation means that even if there were agreed methods of inference
and interpretation, incommensurability could still arise since
scientists might disagree on the nature of the observational data
themselves. 


Kuhn expresses or builds on the idea that participants in different
disciplinary matrices will see the world differently by claiming that
their worlds are different: 



>  In a sense I am unable to explicate further, the
> proponents of competing paradigms practice their trades in different
> worlds. One contains constrained bodies that fall slowly, the other
> pendulums that repeat their motions again and again. In one, solutions
> are compounds, in the other mixtures. One is embedded in a flat, the
> other in a curved, matrix of space. Practicing in different worlds,
> the two groups of scientists see different things when they look from
> the same point in the same direction (1962/1970a, 150).
> 
> 
> 


Remarks such as these gave some commentators the impression that
Kuhn was a strong kind of constructivist, holding that the way the
world literally is depends on which scientific theory is currently
accepted. Kuhn, however, denied any constructivist import to his
remarks on world-change. (The closest Kuhn came to constructivism was
to acknowledge a parallel with Kantian idealism, which is discussed
below in Section 6.4.)


Kuhn likened the change in the phenomenal world to the
Gestalt-switch that occurs when one sees the duck-rabbit diagram first
as (representing) a duck then as (representing) a rabbit, although he
himself acknowledged that he was not sure whether the Gestalt case was
just an analogy or whether it illustrated some more general truth
about the way the mind works that encompasses the scientific case
too.


### 4.3 Kuhn's Early Semantic Incommensurability Thesis


 Although the theory-dependence of observation plays a significant
role in *The Structure of Scientific Revolutions*, neither it
nor methodological incommensurability could account for all the
phenomena that Kuhn wanted to capture with the notion of
incommensurability. Some of his own examples are rather
stretched--for instance he says Lavoisier saw oxygen where
Priestley saw dephlogisticated air, describing this as a
'transformation of vision' (1962/1970a, 118). Moreover
observation--if conceived of as a form of perception--does not
play a significant part in every science. Kuhn wanted to explain his
own experience of reading Aristotle, which first left him with the
impression that Aristotle was an inexplicably poor scientist (Kuhn 1987). But
careful study led to a change in his understanding that allowed him to
see that Aristotle was indeed an excellent scientist. This could not
simply be a matter of literally perceiving things differently. Kuhn
took the incommensurability that prevented him from properly
understanding Aristotle to be at least partly a linguistic, semantic
matter. Indeed, Kuhn spent much of his career after *The Structure
of Scientific Revolutions* attempting to articulate a semantic
conception of incommensurability.


In *The Structure of Scientific Revolutions* Kuhn asserts
that there are important shifts in the meanings of key terms as a
consequence of a scientific revolution. For example, Kuhn says:



> 
> ... the physical referents of these Einsteinian concepts are
> by no means identical with those of the Newtonian concepts that bear
> the same name. (Newtonian mass is conserved; Einsteinian is
> convertible with energy. Only at low relative velocities may the two
> be measured in the same way, and even then they must not be conceived
> to be the same.) (1962/1970a, 102)
> 
>  


This is important, because a standard conception of the transition
from classical to relativistic physics is that although Einstein's
theory of relativity supersedes Newton's theory, what we have is an
improvement or generalization whereby Newton's theory is a special
case of Einstein's (to a close approximation). We can therefore say
that the later theory is closer to the truth than the older
theory. Kuhn's view that 'mass' as used by Newton cannot
be translated by 'mass' as used by Einstein allegedly
renders this kind of comparison impossible. Hence incommensurability
is supposed to rule out convergent realism, the view that science
shows ever improving approximation to the truth. (Kuhn also thinks,
for independent reasons, that the very ideas of matching the truth and similarity
to the truth are incoherent (1970a, 206).)


Kuhn's view as expressed in the passage quoted above depends upon
meaning holism--the claim that the meanings of terms are
interrelated in such a way that changing the meaning of one term
results in changes in the meanings of related terms: "To make
the transition to Einstein's universe, the whole conceptual web whose
strands are space, time, matter, force, and so on, had to be shifted
and laid down again on nature whole." (1962/1970a, 149). The
assumption of meaning holism is a long standing one in Kuhn's
work. One source for this is the later philosophy of
Wittgenstein. Another not unrelated source is the assumption of holism
in the philosophy of science that is consequent upon the positivist
conception of theoretical meaning. According to the latter, it is not
the function of the theoretical part of scientific language to refer
to and describe unobserved entities. Only observational sentences
directly describe the world, and this accounts for them having the
meaning that they do. Theories permit the deduction of observational
sentences. This is what gives theoretical expressions their
meaning. Theoretical statements cannot, however, be reduced to
observational ones. This is because, first, theoretical propositions
are collectively involved in the deduction of observational
statements, rather than singly. Secondly, theories generate
dispositional statements (e.g. about the solubility of a substance,
about how they would appear if observed under certain circumstances,
etc.), and dispositional statements, being modal, are not equivalent
to any truth-function of (non-modal) observation
statements. Consequently, the meaning of a theoretical sentence is not
equivalent to the meaning of any observational sentence or combination
of observational sentences. The meaning of a theoretical term is a
product of two factors: the relationship of the theory or theories of
which it is a part to its observational consequences and the role that
particular term plays within those theories. This is the
double-language model of the language of science and was the standard
picture of the relationship of a scientific theory to the world when
Kuhn wrote *The Structure of Scientific Revolutions*. Kuhn's
challenge to it lay not in rejecting the anti-realism implicit in the
view that theories do not refer to the world but rather in undermining
the assumption that the relationship of observation sentence to the
world is unproblematic. By insisting on the theory-dependence of
observation, Kuhn in effect argued that the holism of theoretical
meaning is shared by apparently observational terms also, and for this
reason the problem of incommensurability cannot be solved by recourse
to theory-neutral observation sentences.


(Although it is true that Kuhn uses the expression 'physical
referent' in the passage quoted above, this should not be taken
to mean an independently existing worldly entity. If that were the
case, Kuhn would be committed to the worldly existence of both
Newtonian mass and Einsteinian mass (which are nonetheless not the
same). It is implausible that Kuhn intended to endorse such a view. A
better interpretation is to understand Kuhn as taking reference, in
this context, to be a relation between a term and a hypothetical
rather than worldly entity. Reference of anything like the Fregean,
worldly kind plays no part in Kuhn's thinking. Again this may be seen
as a reflection of the influence of one or other or both of the
(later) Wittgensteinian downplaying of reference and of the positivist
view that theories are not descriptions of the world but are in one
way or another tools for the organization or prediction of
observations.)


### 4.4 Kuhn's Later Semantic Incommensurability Thesis


Although Kuhn asserted a semantic incommensurability thesis in
*The Structure of Scientific Revolutions* he did not there
articulate or argue for the thesis in detail. This he attempted in
subsequent work, with the result that the nature of the thesis changed
over time. The heart of the incommensurability thesis after *The
Structure of Scientific Revolutions* is the idea that certain
kinds of translation are impossible. Early on Kuhn drew a parallel
with Quine's thesis of the indeterminacy of translation (1970a, 202;
1970c, 268). According to the latter, if we are translating one
language into another, there are inevitably a multitude of ways of
providing a translation that is adequate to the behaviour of the
speakers. None of the translations is the uniquely correct one, and in
Quine's view there is no such thing as the meaning of the words to be
translated. It was nonetheless clear that Quine's thesis was rather
far from Kuhn's thesis, indeed that they are incompatible. First, Kuhn
thought that incommensurability was a matter of there being no fully
adequate translation whereas Quine's thesis involved the availability
of multiple translations. Secondly, Kuhn does believe that the
translated expressions do have a meaning, whereas Quine denies
this. Thirdly, Kuhn later went on to say that unlike Quine he does not
think that reference is inscrutable--it is just very difficult to
recover (1976, 191). 


Subsequently, Kuhn developed the view that incommensurability
arises from differences in classificatory schemes. This is taxonomic
incommensurability. A field of science is governed by a taxonomy,
which divides its subject matter into kinds. Associated with a
taxonomy is a lexical network--a network of related terms. A
significant scientific change will bring with it an alteration in the
lexical network which in turn will lead to a re-alignment of the
taxonomy of the field. The terms of the new and old taxonomies will
not be inter-translatable.


The problematic nature of translation arises from two
assumptions. First, as we have seen, Kuhn assumes that meaning is
(locally) holistic. A change in the meaning of one part of the lexical
structure will result in a change to all its parts. This would rule
out preservation of the translatability of taxonomies by redefining
the changed part in terms of the unchanged part. Secondly, Kuhn adopts
the 'no-overlap' principle which states that categories in
a taxonomy must be hierarchically organised: if two categories have
members in common then one must be fully included within the other;
otherwise they are disjoint--they cannot simply overlap. This
rules out the possibility of an all-encompassing taxonomy that
incorporates both the original and the changed taxonomies. (Ian
Hacking (1993) relates this 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*.)


Kuhn continued to develop his conceptual approach to
incommensurability. At the time of his death he had made considerable
progress on a book in which he related incommensurability to issues in
developmental psychology and concept acquisition.


## 5. History of Science


 Kuhn's historical work covered several topics in the history of
physics and astronomy. During the 1950s his focus was primarily on the
early theory of heat and the work of Sadi Carnot. However, his first
book concerned the Copernican revolution in planetary astronomy
(1957). This book grew out of the teaching he had done on James
Conant's General Education in Science curriculum at Harvard but also
presaged some of the ideas of *The Structure of Scientific
Revolutions*. In detailing the problems with the Ptolemaic system
and Copernicus' solution to them, Kuhn showed two things. First,
he demonstrated that Aristotelian science was genuine science and that
those working within that tradition, in particular those working on
Ptolemaic astronomy, were engaged in an entirely reasonable and
recognizably scientific project. Secondly, Kuhn showed that Copernicus
was himself far more indebted to that tradition than had typically
been recognized. Thus the popular view that Copernicus was a modern
scientist who overthrew an unscientific and long-outmoded viewpoint is
mistaken both by exaggerating the difference between Copernicus and
the Ptolemaic astronomers and in underestimating the scientific
credentials of work carried out before Copernicus. This mistaken
view--a product of the distortion caused by our current state of
knowledge--can be rectified only by seeing the activities of
Copernicus and his predecessors in the light of the puzzles presented
to them by tradition that they inevitably had to work with. While Kuhn
does acknowledge the influence of causes outside science (such as a
resurgence in Sun worship (1962/70a, 152-3)), he nonetheless
emphasizes the fact that astronomers were responding primarily to
problems raised within science. What appealed to them in
Copernicus' model was its ability to do away with ad hoc devices
in Ptolemy's system (such as the equant), to explain key phenomena in
a pleasing fashion (the observed retrograde motion of the planets),
and to explain away otherwise inexplicable coincidences in Ptolemy's
system (such as the alignment of the Sun and the centres of the
epicycles of the inferior planets).


In the 1960s Kuhn's historical work turned toward the early history
of quantum theory, culminating in his book *Black-Body Theory and
the Quantum Discontinuity*. According to classical physics a
particle could possess any energy in a continuous range and if it
changes energy it does so in a continuous fashion, possessing at some
point in time every energy between the initial and final energy
states. Modern quantum theory denies both these classical
principles. Energy is quantised--a particle may possess only one
of a set of discrete energies. Consequently if it changes in energy
from one value to the next permitted value it does so discontinuously,
jumping straight from one energy to the other without taking any of
the intermediate ('forbidden') values. In order to explain
the distribution of energy within a cavity (black-body radiation),
Planck used the device of dividing up the energy states into multiples
of the unit or 'quantum' *h*n (where n is the
frequency of radiation and *h* is what subsequently became
known as Planck's constant). Planck did this in order to employ a
statistical technique of Boltzmann's whereby the range of possible
*continuous* energies is divided into 'cells' of
similar energies that could be treated together for mathematical
purposes. Kuhn notes that Planck was puzzled that in carrying out his
derivation, only by fixing the cell size at *h*n could he
get the result he wanted--the technique should have worked for any
way of dividing the cells, so long as they were small enough but not
too small. This work of Planck's was carried out in the period 1900-1,
which is the date tradition has accorded to the invention of the
quantum concept. However, argued Kuhn, Planck did not have in mind a
genuine physical discontinuity of energies until 1908, which is after
Albert Einstein and Paul Ehrenfest had themselves emphasized it in
1905-6.


 Many readers were surprised not to find mention of paradigms or
incommensurability. Kuhn later added an Afterword, "Revisiting
Planck", explaining that he had not repudiated or ignored those
ideas but that they were implicit in the argument he gave. Indeed the
whole essay may be seen as a demonstration of an incommensurability
between the mature quantum theory and the early quantum theory of
Planck which was still rooted in classical statistical physics. In
particular the very term 'quantum' changed its meaning
between its introduction by Planck and its later use. Kuhn argues that
the modern quantum concept was introduced first not by Planck but by
Einstein. Furthermore, this fact is hidden both by the continued use
of the same term and by the same distortion of history that has
affected our conception of Ptolemy and Copernicus. As in
Copernicus' case, Planck has been seen as more revolutionary
than in fact he was. In Planck's case, however, this misconception was
also shared by Planck himself later in life.


## 6. Criticism and Influence


Kuhn's work met with a largely critical reception among
philosophers. Some of this criticism became muted as Kuhn's work
became better understood and as his own thinking underwent
transformation. At the same time other developments in philosophy
opened up new avenues for criticism. That criticism has largely
focussed on two areas. First, it has been argued that Kuhn's account
of the development of science is not entirely accurate. Secondly,
critics have attacked Kuhn's notion of incommensurability, arguing
that either it does not exist or, if it does exist, it is not a
significant problem. Despite this criticism, Kuhn's work has been
hugely influential, both within philosophy and outside it. *The
Structure of Scientific Revolutions* was an important stimulus to
what has since become known as 'Science Studies', in particular the
Sociology of Scientific Knowledge (SSK).


### 6.1 Scientific Change


In *The Structure of Scientific Revolutions* periods of
normal science and revolutionary science are clearly distinguished.
In particular paradigms and their theories are not questioned and not
changed in normal science whereas they are questioned and are changed
in revolutionary science. Thus a revolution is, by definition
revisionary, and normal science is not (as regards
paradigms). Furthermore, normal science does not suffer from the
conceptual discontinuities that lead to incommensurability whereas
revolutions do. This gives the impression, confirmed by Kuhn's
examples, that revolutions are particularly significant and reasonably
rare episodes in the history of science.


This picture has been questioned for its accuracy. Stephen Toulmin
(1970) argues that a more realistic picture shows that revisionary
changes in science are far more common and correspondingly less
dramatic than Kuhn supposes, and that perfectly 'normal'
science experiences these changes also. Kuhn could reply that such
revisions are not revisions to the paradigm but to the non-paradigm
puzzle-solutions provided by normal science. But that in turn
requires a clear distinction between paradigmatic and non-paradigmatic
components of science, a distinction that, arguably, Kuhn has not
supplied in any detail.


At the same time, by making revisionary change a necessary
condition of revolutionary science, Kuhn ignores important discoveries
and developments that are widely regarded as revolutionary, such as
the discovery of the structure of DNA and the revolution in molecular
biology. Kuhn's view is that discoveries and revolutions come about
only as a consequence of the appearance of anomalies. Yet it is also
clear that a discovery might come about in the course of normal
science and initiate a 'revolution' (in a non-Kuhnian
sense) in a field because of the unexpected insight it provides and
the way it opens up opportunities for new avenues of research. The
double-helical structure of DNA was not expected but immediately
suggested a mechanism for the duplication of genetic information
(e.g. in mitosis), which had enormous consequences for subsequent
biological research.


### 6.2 Incommensurability


Kuhn's incommensurability thesis presented a challenge not only to
positivist conceptions of scientific change but also to realist ones.
For a realist conception of scientific progress also wishes to assert
that, by and large, later science improves on earlier science, in
particular by approaching closer to the truth. A standard realist
response from the late 1960s was to reject the anti-realism and
anti-referentialism shared by both Kuhn's picture and the preceding
double-language model. 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. As we have seen, Kuhn thinks that we cannot
properly say that Einstein's theory is an improvement on Newton's in
the sense that the latter as deals reasonably accurately
(only) with a special case of the former. Whether or not the key terms
(such as 'mass') in the two theories differ in meaning, a
realist and referentialist approach to theories permits one to say
that Einstein's theory is closer to the truth than Newton's. For truth
and nearness to the truth depend only on reference and not on
sense. Two terms can differ in sense yet share the same reference, and
correspondingly two sentences may relate to one another as regards
truth without their sharing terms with the same sense. And so even if
we retain a holism about the sense of theoretical terms and allow that
revolutions lead to shifts in sense, there is no direct inference from
this to a shift in reference. Consequently, there is no inference to
the inadmissibility of the comparison of theories with respect to
their truth-nearness.


While this referentialist response to the incommensurability thesis
was initially framed in Fregean terms (Scheffler 1967), it received
further impetus from the work of Kripke (1980) and Putnam (1975b),
which argued that reference could be achieved without anything akin to
Fregean sense and that the natural kind terms of science exemplified
this sense-free reference. In particular, causal theories of reference
permit continuity of reference even through fairly radical theoretical
change. (They do not guarantee continuity in reference, and changes in
reference can occur on some causal theories, e.g. Gareth Evans's
(1973). Arguing that they do occur would require more, however, than
merely pointing to a change in theory. Rather, it seems, cases of
reference change must be identified and argued for on a case by case
basis.) Therefore, if taken to encompass terms for quantities and
properties (such as 'mass'), the changes that Kuhn
identified as changes in meaning (e.g. those involved in the shift
from Newtonian to relativistic physics) would not necessarily be
changes that bear on reference, nor, consequently, on comparison for
nearness to the truth. The simple causal theory of reference does
have its problems, such as explaining the referential mechanism of
empty theoretical terms (e.g.caloric and phlogiston) (c.f. Enc
1976, Nola 1980). Causal-descriptive theories (which allow for a
descriptive component) tackle such problems while retaining the key
idea that referential continuity is possible despite radical theory
change (Kroon 1985, Sankey 1994).


Of course, the referentialist response shows only that reference
can be retained, not that it must be. Consequently it is only a
partial defence of realism against semantic incommensurability. A
further component of the defence 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. Methodological
incommensurability in particular seems to threaten the possibility of
this knowledge. 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-what he calls an 'Archimedean platform'
(1992, 14). However, we never are able to escape from our current
perspective. A realist response to this kind of incommensurability may
appeal to externalist or naturalized epistemology. These (related)
approaches reject the idea that for a method to yield knowledge it
must be independent of any particular theory, perspective, or
historical/cognitive circumstance. So long as the method has an
appropriate kind of reliability it can generate knowledge. Contrary
to the internalist view characteristic of the positivists (and, it
appears, shared by Kuhn) the reliability of a method does not need to
be one that must be evaluable independently of any particular
scientific perspective. It is not the case, for example, that the
reliability of a method used in science must be justifiable by a
priori means. Thus the methods developed in one era may indeed
generate knowledge, including knowledge that some previous era got
certain matters wrong, or right but only to a certain degree. A
naturalized epistemology may add that science itself is in the
business of investigating and developing methods. As science develops
we would expect its methods to change and develop also.


### 6.3 Kuhn and Social Science


Kuhn's influence outside of professional philosophy of science may
have been even greater than it was within it. The social sciences in
particular took up Kuhn with enthusiasm. There are primarily two
reasons for this. First, Kuhn's picture of science appeared to permit
a more liberal conception of what science is than hitherto, one that
could be taken to include disciplines such as sociology and
psychoanalysis. Secondly, Kuhn's rejection of rules as determining
scientific outcomes appeared to permit appeal to other factors,
external to science, in explaining why a scientific revolution took
the course that it did.


The status as genuine sciences of what we now call the social and
human sciences has widely been held in doubt. Such disciplines lack
the remarkable track record of established natural sciences and seem
to differ also in the methods they employ. More specifically they
fail by pre-Kuhnian philosophical criteria of sciencehood. On the one
hand, positivists required of a science that it should be verifiable
by reference to its predictive successes. On the other, Popper's
criterion was that a science should be potentially falsifiable by a
prediction of the theory. Yet psychoanalysis, sociology and even
economics have difficulty in making precise predictions at all, let
alone ones that provide for clear confirmation or unambiguous
refutation. Kuhn's picture of a mature science as being dominated by
a paradigm that generated sui generis puzzles and criteria for
assessing solutions to them could much more easily accommodate these
disciplines. For example, Popper famously complained that
psychoanalysis could not be scientific because it resists
falsification. Kuhn's account argues that resisting falsification is
precisely what *every* disciplinary matrix in science does.
Even disciplines that could not claim to be dominated by a settled
paradigm but were beset by competing schools with different
fundamental ideas could appeal to Kuhn's description of the
pre-paradigm state of a science in its infancy. Consequently Kuhn's
analysis was popular among those seeking legitimacy as science (and
consequently kudos and funding) for their new disciplines. Kuhn
himself did not especially promote such extensions of his views, and
indeed cast doubt upon them. He denied that psychoanalysis is a
science and argued that there are reasons why some fields within the
social sciences could not sustain extended periods of puzzle-solving
normal science (1991b). Although, he says, the natural sciences
involve interpretation just as human and social sciences do, one
difference is that hermeneutic re-interpretation, the search for new
and deeper intepretations, is the essence of many social scientific
enterprises. This contrasts with the natural sciences where an
established and unchanging interpretation (e.g. of the heavens) is a
pre-condition of normal science. Re-intepretation is the result of a
scientific revolution and is typically resisted rather than actively
sought. Another reason why regular reinterpretation is part of the
human sciences and not the natural sciences is that social and
political systems are themselves changing in ways that call for new
interpretations, whereas the subject matter of the natural sciences is
constant in the relevant respects, permitting a puzzle-solving
tradition as well as a standing source of revolution-generating
anomalies.


A rather different influence on social science was Kuhn's influence
on the development of social studies of science itself, in particular
the 'Sociology of Scientific Knowledge'. A central claim
of Kuhn's work is that scientists do not make their judgments as the
result of consciously or unconsciously following rules. Their
judgments are nonetheless tightly constrained during normal science by
the example of the guiding paradigm. During a revolution they are
released from these constraints (though not completely). Consequently
there is a gap left for other factors to explain scientific judgments.
Kuhn himself suggests in *The Structure of Scientific
Revolutions* that Sun worship may have made Kepler a Copernican
and that in other cases, facts about an individual's life history,
personality or even nationality and reputation may play a role
(1962/70a, 152-3). Later Kuhn repeated the point, with the additional
examples of German Romanticism, which disposed certain scientists to
recognize and accept energy conservation, and British social thought
which enabled acceptance of Darwinism (1977c, 325). Such suggestions
were taken up as providing an opportunity for a new kind of study of
science, showing how social and political factors external to science
influence the outcome of scientific debates. In what has become known
as social constructivism/constructionism (e.g. Pickering 1984) this
influence is taken to be central, not marginal, and to extend to the
very content of accepted theories. Kuhn's claim and its exploitation
can be seen as analogous to or even an instance of the exploitation of
the (alleged) underdetermination of theory by evidence (c.f. Kuhn
1992, 7). Feminists and social theorists (e.g. Nelson 1993) have
argued that the fact that the evidence, or, in Kuhn's case, the shared
values of science, do not fix a single choice of theory, allows
external factors to determine the final outcome (see Martin 1991 and
Schiebinger 1999 for feminist social constructivism). Furthermore,
the fact that Kuhn identified *values* as what guide judgment
opens up the possibility that scientists ought to employ different
values, as has been argued by feminist and post-colonial writers
(e.g. Longino 1994).


Kuhn himself, however, showed only limited sympathy for such
developments. In his "The Trouble with the Historical Philosophy
of Science" (1992) Kuhn derides those who take the view that in
the 'negotiations' that determine the accepted outcome of
an experiment or its theoretical significance, *all* that
counts are the interests and power relations among the
participants. Kuhn targeted the proponents of the Strong Programme in
the Sociology of Scientific Knowledge with such comments; and even if
this is not entirely fair to the Strong Programme, it reflects Kuhn's
own view that the primary determinants of the outcome of a scientific
episode are to be found within science. External history of science
seeks causes of scientific change in social, political, religious and
other developments of science. Kuhn sees his work as "pretty
straight internalist" (2000: 287). First, the five values Kuhn
ascribes to all science are in his view constitutive of science. An
enterprise could have different values but it would not be science
(1977c, 331; 1993, 338). Secondly, when a scientist is influenced by
individual or other factors in applying these values or in coming to a
judgment when these values are not decisive, those influencing factors
will typically themselves come from within science (especially in
modern, professionalized science). Personality may play a role in the
acceptance of a theory, because, for example, one scientist is more
risk-averse than another (1977c, 325)--but that is still a
relationship to the scientific evidence. Even when reputation plays a
part, it is typically *scientific* reputation that encourages
the community to back the opinion of an eminent scientist. Thirdly,
in a large community such variable factors will tend to cancel out.
Kuhn supposes that individual differences are normally distributed and
that a judgment corresponding to the mean of the distribution will
also correspond to the judgment that would, hypothetically, be
demanded by the rules of scientific method, as traditionally conceived
(1977c, 333). Moreover, the existence of differences of response
within the leeway provided by shared values is crucial to science,
since it permits "rational men to disagree" (1977c, 332)
and thus to commit themselves to rival theories. Thus the looseness
of values and the differences they permit "may . . . appear an
indispensable means of spreading the risk which the introduction or
support of novelty always entails" (Ibid.).


### 6.4 Recent Developments


Even if Kuhn's work has not remained at the centre of the
philosophy of science, a number of philosophers have continued to find
it fruitful and have sought to develop it in a number of
directions. Paul Hoyningen-Huene (1989/1993), as a result of working
with Kuhn, developed an important neo-Kantian interpretation of his
discussion of perception and world-change. We may distinguish between
the world-in-itself and the 'world' of our perceptual and
related experiences (the phenomenal world). This corresponds to the
Kantian distinction between noumena and phenomena. The important
difference between Kant and Kuhn is that Kuhn takes the general form
of phenomena not to be fixed but changeable. A shift in paradigm can
lead, via the theory-dependence of observation, to a difference in
one's experiences of things and thus to a change in one's phenomenal
world. This change in phenomenal world articulates the sense in which
the world changes as a result of a scientific revolution while also
capturing Kuhn's claims about the theory-dependence of observation and
consequent incommensurability (Hoyningen-Huene 1990).


A rather different direction in which Kuhn's thought has been
developed proposes that his ideas might be illuminated by advances in
cognitive psychology. One the one hand work on conceptual structures
can help understand what might be correct in the incommensurability
thesis (Nersessian 1987, 2003). Several authors have sought in
different ways to emphasize what they take to be the Wittgensteinian
element in Kuhn's thought (for example Kindi 1995, Sharrock and Read
2002). Andersen, Barker, and Chen (1996, 1998, 2006) draw in
particular on Kuhn's version of Wittgenstein's notion of family
resemblance. Kuhn articulates a view according to which the extension
of a concept is determined by similarity to a set of exemplary cases
rather than by an intension. Andersen, Barker, and Chen argue that
Kuhn's view is supported by the work of Rosch (1972; Rosch and Mervis
1975) on prototypes; furthermore, this approach can be developed in
the context of dynamic *frames* (Barsalou 1992), which can then
explain the phenomenon of (semantic) incommensurability.


On the other hand, the psychology of analogical thinking and
cognitive habits may also inform our understanding of the concept of a
paradigm. Kuhn himself tells us that "The paradigm as shared
example is the central element of what I now take to be the most novel
and least understood aspect of [*The Structure of Scientific
Revolutions*]" (1970a, 187). Kuhn, however, failed to
develop the paradigm concept in his later work beyond an early
application of its semantic aspects to the explanation of
incommensurability. Nonetheless, other philosophers, principally
Howard Margolis (1987, 1993) have developed the idea that habits of
mind formed by training with paradigms-as-exemplars are an important
component in understanding the nature of scientific development. As
explained by Nickles (2003b) and Bird (2005), this is borne out by
recent work by psychologists on model-based and analogical thinking.


### 6.5 Assessment


Assessing Kuhn's significance presents a conundrum. Unquestionably
he was one of the most influential philosophers and historians of
science of the twentieth century. His most obvious achievement was to
have been a major force in bringing about the final demise of logical
positivism. Nonetheless, there is no characteristically Kuhnian
school that carries on his positive work. It is as if he himself
brought about a revolution but did not supply the replacement
paradigm. For a period in the 1960s and 1970s it looked as if there
was a Kuhnian paradigm 'historical philosophy of science',
flourishing especially in newly formed departments of history and
philosophy of science. But as far as the history of science and
science studies more generally are concerned, Kuhn repudiated at least
the more radical developments made in his name. Indeed part of Kuhn's
fame must be due to the fact that both his supporters and his
detractors took his work to be more revolutionary (anti-rationalist,
relativist) than it really was.


Turning to the philosophy of science, it was clear by the end of
the 1980s that the centreground was now occupied by a new realism, one
that took on board lessons from general philosophy of language and
epistemology, in particular referentialist semantics and a belief in
the possibility of objective knowledge and justification. There is
some irony therefore in the fact that it was the demise of logical
positivism/empiricism that led to the rebirth of scientific realism
along with causal and externalist semantics and epistemology,
positions that Kuhn rejected.


One way of understanding this outcome is to see that Kuhn's
relationship on the one hand to positivism and on the other hand to
realism places him in an interesting position. Kuhn's thesis of the
theory-dependence of observation parallels related claims by
realists. In the hands of realists the thesis is taken to undermine
the theory-observation dichotomy that permitted positivists to take an
anti-realist attitude to theories. In the hands of Kuhn however, the
thesis is taken, in effect, to extend anti-realism from theories to
observation also. This in turn fuels the thesis of
incommensurability. The fact that incommensurability is founded upon a
response to positivism diametrically opposed to the realist response
explains why much of Kuhn's later philosophical work, which developed
the incommensurability thesis, has had little impact on the majority
of philosophers of science.


The explanation of scientific development in terms of paradigms was
not only novel but radical too, insofar as it gives a naturalistic
explanation of belief-change. Naturalism was not in the early 1960s
the familiar part of philosophical landscape that it has subsequently
become. Kuhn's explanation contrasted with explanations in terms of
rules of method (or confirmation, falsification etc.) that most
philosophers of science took to be constitutive of
rationality. Furthermore, the relevant disciplines (psychology,
cognitive science, artificial intelligence) were not then advanced
enough to to support Kuhn's contentions concerning paradigms, or those
disciplines were antithetical to Kuhn's views (in the case of
classical AI). Now that naturalism has become an accepted component of
philosophy, there has recently been interest in reassessing Kuhn's
work in the light of developments in the relevant sciences, many of
which provide corroboration for Kuhn's claim that science is driven by
relations of perceived similarity and analogy. It may yet be that a
characteristically Kuhnian thesis will play a prominent part in our
understanding of science.