Kuhn, Thomas

"Scientific theories cannot be purely empirical; they must contain speculative elements."

"A scientist must believe that the science he practices is valuable."

"The way science is actually practiced is far more complex than textbooks suggest."

"Deep conceptual schemes and values are often shared by entire communities and not easily questioned."

"Once it has achieved the status of paradigm, a scientific theory is declared invalid only if an alternate candidate is available to take its place."

"The presence of crises, the recourse to extraordinary measures, all these changes of gear performed by the community, are characteristically associated with periods in which paradigm shift occurs."

"What scientists think they are doing and what they really do are two different things."

"Competition between segments of the scientific community is the only process known which regularly results in the rejection of standard theories."

"Scientific training is the inculcation of a very particular constellation of mental habits and predispositions."

"Progress is not a permanent feature of science, nor does it occur in every field."

"The scientist does not ask nature in general; he has learned to ask very particular concrete questions with every expectation of getting precise answers."

"Observation and experience can and must drastically restrict the range of admissible beliefs, else there would be no science."

"A field of science dominated by one paradigm develops in a very different way from one which has learned to live with competing paradigms."

"What is the mechanism by which a new paradigm finally supplants its predecessor?"

"The scientific enterprise as a whole does progress, and we do not mistake that sense of progress for a mere bias."

"Anomalies are not simply ignored; they are the stuff of which scientific revolutions are made."

"The pre-paradigm period is often characterized by schools of thought rather than unified scientific effort."

"Science is not a progression of absolute or cumulative truths but rather a succession of paradigm shifts."

"The decision to employ a new paradigm involves a comparison of both paradigms with nature and with the problem they came to solve."

"What has been seen once or twice can always be seen again—but not necessarily by the same observational route."

"Kuhnian revolutions are not metaphorical but literal overturnings of conceptual worlds."

"The vocabulary of science is not value-free; it embeds assumptions about reality."

"A scientific community unified by one paradigm is more productive than one fractured by competing schools."

"The problems that emerge during the crisis stage are those that the existing paradigm can neither adequately define nor solve."

"For many decades Einstein's equations were treated as axiomatic, yet they were derived, not revealed."

"An anomaly appears only against the background of an expectation."

"Scientists are not engaged in discovering the world as it is in itself; they are engaged in solving puzzles."

"Conceptual revolutions often seem sudden because what changes is not so much the data as the way in which the data is interpreted."

"It is as if the professional community had committed itself to playing a game in which only certain moves are legal."

"A successful theory can be superseded not because it is falsified but because something better comes along."