Kuhn, T. S. (1970). The Structure of Scientific
Revolutions. Chicago, University of Chicago Press.
The idea of "development by accumulation" seems not to work for
historians. Ideas from past eras don't simply fit seamlessly into the next
one. There is an historical integrity to a given scientific era that is
often ignored in textbooks.
Early development stages in most sciences is marked by competition between
a number of distinct schools, ultimately resulting in the adoption of one
school as a paradigm. Normal science proceeds between paradigm shifts.
p. 5 "Normal science, the activity which most scientists spend almost
all their time, is predicated on the assumption that the scientific community
knows what the world is like" Usually, normal science supresses alternative
views. However sometimes anomalies that can't be satisfactorily explained
by normal science . p. 6 "and when it does -- when, that is the profession
can no longer evade anomalies that subvert the existing tradition of scientific
practice -- then begin the extraordinary investigations that lead the profession
at last to a new set of commitments, a new basis for the practice of science".
These extraordinary episodes are scientific revolutions.
Scientific revolutions don't merely add another fact but completely destroy
previous conceptual understandings. Scientific fact and theory are not
p. 7 "That is why the unexpected discovery is not simply factual in
its import and why the scientist's world is qualitatively transformed as
well as quantitatively enriched by fundamental novelties of either fact
Section II: The Route to Normal Science
Normal science is "research firmly based upon one or more past scientific
achievements, achievements that some particular scientific community acknowledges
for a time as supplying the foundation for further practice" p. 10
Often these advances are described in textbooks, which rewrite previous
theories to seem that they have logically and inevitably led to the current
"The study of paradigms ... is what mainly prepares the student for
membership in the particular scientific community with which he will later
Once a paradigm emerges people either convert, get ignored, or eventually
retire and leave the profession. Eventually a consensus is reached on what
to believe and how to practice in the field, which is taught to new students
and re-enacted through journals, conferences, etc.
Normal science progresses fastest when there is a strong paradigm, because
everyone knows what the rules are and the criteria for evaluation. Most
new knowledge is found in journal articles, with textbooks primarily used
for paradigm socialization of newcomers. Only in the pre-paradigm stages
are textbooks seen as influential.
III. The Nature of Normal Science
p. 23 "Paradigms gain their status because they are more successful
than their competitors in solving a few problems that the group of practioners
has come to recognize as acute". Normal science is a "mopping
up" exercise of theory refinement and extension.
IV. Normal Science as Puzzle Solving
Normal research doesn't aim to produce novelities.
"...one of the things a scientific community acquires with a paradigm
is a criterion for choosing problems that, while the paradigm is taken for
granted, can be assumed to have solutions" p. 37 "One of the
reasons why normal science seems to progress so rapidly is that its practioners
concentrate on problems that only their own lack of ingenuity should keep
them from solving". p. 37 The paradigm dictates the rules of the
V. The priority of paradigms
A paradigm doesn't have to be consensually articulated or understood for
it to influence research.
p. 47 "as the student proceeds from his freshman course to and through
his doctoral dissertation, the problems assigned to him become more complex
and less completely precedented. But they continue to be closely modeled
on previous achievements as are the problems that normally occupy him during
his subsequent independent career".
Paradigms often proceed the formal articulation of rules.
p. 50 "What (quantum mechanics" means to each of them depends
on what courses he has had, what texts he has read, and which journals he
VI. Anomaly and the Emergence of Scientific Discoveries
p. 52 "Discovery commences with the awareness of anomaly, i.e., with
the recognition that nature has somehow violated the paradigm-induced expectations
that goven normal science. It then continues with a more or less extended
exploration of the area of anomaly. And it closes only when the paradigm
theory has been adjusted so that the anomalous ha become the expected".
"In the development of any science, the first received paradigm is
usually felt to account quite successfully for most of the observations
and experiments easily accessible to that science's practitioners. Further
development, therefore, ordinarily calls for the construction of elaborate
equipment, the development of an esoteric vocabulary and skills, and a refinement
of concepts that increasingly lessens their resemblence to their usual common-sense
prototypes. That professionalization leads, on the one hand, to an immense
restriction of the scientist's vision and ao a considerable resistance to
paradigm change. The science has become increasingly rigid. On the other
hand, within those areas to which the paradigm directs the attention of
the group, normal science leads to a detail of information and to a precision
of the observation-theory match that could be achieved in no other way.
.... Anomaly appears only against the background provided by the paradigm".
Normal science "prepares the way for its own change".
VII. Crisis and The Emergence of Scientific Theories
p. 67 "Because it demands large-scale paradigm destruction and major
shifts in the problems and techniques of normal science, the emergence of
new theories is generally proceded by a period of pronounced professional
insecurity". The new anomalies start to produce a crisis in the
current paradigm, leading to an collective acceptance to consider new theoretical
ideas. Until then paradigm-challenging ideas will gain little consideration
VIII. The response to crisis
p. 77 "...a scientific theory is declared invalid only if an alternate
candidate is available to take it's place" "The decision to reject
one paradigm is always simultaneously the decision to accept another, and
the judgment leading to that decision involves the comparison of both paradigms
with nature and with each other".
Initially scientists will develop ad hoc explanations to anomalies based
on the current paradigm. Over time the persistance of anomalies will spur
rival theory development. Most anomalies actually do with time become understood
within the existing paradigm. There are always discrepancies with any paradigm.
"persistent and recognized anomaly doesn't always induce crisis"
If the anomaly persists and becomes a focus of research for the field, it
has the potential for inducing a paradigm shift. p. 84 "All crises
begin with the blurring of a paradigm and the consequent loosening of the
rules for normal research".
The new paradigm causes a "reconstruction of the field from new fundamentals"
p. 85 "When the transition is complete, the profession will have changed
its view of the field, its methods, and its goals". p. 85
"Almost always the men who achieve these fundamental inventions of
a new paradigm have been either very young or very new to the field whose
paradigm they change". p. 90 These are the men "being little
commited by prior practice to the traditional rules of normal science, are
particularily likely to see that those rules no longer define a playable
game and to conceive another set that can replace them".
IX. The nature and necessity of scientific revolutions
Note that the "issue of paradigm choice is not settled by logic and
experiment alone". New paradigms make different predictions and emphasize
different things. People argue from different paradigms. Usually the problem
is that paradigms extend "to areas and to degress of precision for
which there is no full precedent" p. 100 Paradigm shifts occur cognitively
p. 109 "In particular, our most recent examples show that paradigms
provide scientists not only with a map but also with some of the directions
essential for map-making. In learning a paradigm the scientist acquires
theory, methods, and standards together, usually in an inextricable mixture.
Therefore, when paradigms change, there are usually significant shifs in
the criteria determining the legitimacy both of problems and of proposed
X. Revolutions as changes of world view
"Led by a new paradigm, scientists adopt new instruments and look in
new places. Even more important, during revolutions scientists see new and
different things when looking with familiar instruments in places they have
looked before". p. 111 Hanover's study with upside-down glasses is
a nice example of getting used to a new perspective.
Once scientists make the shift they can't go back.
XI. The invisibility of revolutions
Most textbooks disguise scientific revolutions as accumulated knowledge.
"...the whole network of fact and theory that the textbook paradigm
fits to nature has shifted". p. 141 They change the previous information
into facts that weren't actually present in prior paradigm.
XII. The resolution of revolutions
Sometimes one paradigm is proven, sometimes the prior one is falsified.
It's hard because people in both paradigms see and define and evaluate
priorities differently. Mostly the new paradigm succeeds because is solves
the crisis in the prior paradigm.
Xiii. progress through revolutions
The parade of normal science punctuated by paradigm shifts is actually a
good way of making progress.