Notes on Kuhn, Chapters 7 and 8
 A crisis occurs when scientists’ awareness of anomaly last so
long and penetrates so deeply that a “period of pronounced
professional insecurity” results from “the persistent failure of
the puzzles of normal science to come out as they should.
 Crises often, but not always, precede paradigm changes.
Paradigm changes that are caused by discoveries of new
phenomena (e.g., X-rays) need not be preceded by crises.
Paradigm changes that involve changes of theory are typically
preceded by crises.
 The increase in the complexity of a theory in response to
anomalies is one factor that leads to crisis. “External factors—
i.e., non-technical factors that are not directly related to
scientists’ success or failure in dealing with anomalies (political
or social pressures, for example)—also contribute to crises.
 Among the paradigm changes that involved theory change
preceded by crisis are
o the replacement of Ptolemy’s geocentric paradigm with
Copernicus’s heliocentric paradigm
o the replacement of the phlogistic paradigm with Lavoisier’s
oxygen theory of combustion
o the replacement of the Newtonian paradigm with Einstein’s
relativistic paradigm
 During a crisis, different versions of the current theory emerge
to deal with troublesome anomalies. The research resulting from
this proliferation of versions of the theory resembles the sort of
activity that occurs in the pre-science phase in which competing
schools vie for dominance.
 Crisis “loosens the rules of normal puzzle-solving in ways that
ultimately permit a new paradigm to emerge.”
 Crises are sometimes necessary for paradigm changes to occur.
For example, Copernicus’s heliocentric theory was proposed
centuries earlier by Aristarchus. However, because at that time
there was no scientific crisis that Aristarchus’s theory would
have resolved, it was ignored.
 Scientists do not renounce paradigms just because they are
confronted with anomalies; paradigms are rejected only when
an alternative paradigm is available to replace it.
o Research in an area of science cannot occur without some
paradigm or other.
o Without anomalies, there is no such thing as research in an
area of science.
 Anomalies, even “stubborn” ones, usually do not lead to crisis
but are rather resolved within normal practice.
 There is probably no general answer to the question of why
some anomalies and not others become the focus of scientists’
attention. Among the reasons are that
1. the anomaly calls into question “explicit and fundamental
generalizations of the paradigm”
2. the anomaly prevents the solution of practical problems that
have special importance (e.g., Ptolemaic astronomy and
calendar reform)
3. the development of normal science may transform the
anomaly into a source of crisis
 As a scientific crisis develops and deepens because of an
anomaly, the existing paradigm undergoes numerous
articulations in order to resolve the anomaly. This process may
advance to the point at which scientists no longer agree what the
paradigm is.
 Crises in science end in one of three ways:
1. The anomalies that precipitated the crisis are handled within
normal science.
2. The problem resists all attempted solutions and is simply
deferred to a later time.
3. A new candidate for paradigm emerges and competes against
the current paradigm.
 In times of crisis, scientists often turn to philosophical analysis
in order to identify and clarify the fundamental assumptions of
their fields and to escape the grip of the normal science tradition
that (they sense) is impeding them from solving the problems at
the heart of the crisis. One way in which they do this is by
conducting thought experiments.
 The difficulty in escaping from the grip of the existing paradigm
is evidenced by the fact that scientists who invent new
paradigms are almost always very young or very new to the
field.
 Extraordinary science is the kind of science that goes on during
a crisis, in which there is a “breakdown in normal scientific
activity.”
 Symptoms of the transition from normal science to
extraordinary science include
1. the proliferation of competing articulations of the existing
paradigm
2. scientists’ willingness to try anything
3. the explicit expression of discontent with the current
paradigm
4. the recourse to philosophy and to debate over fundamentals