The Structure of Scientific Revolutions

by Thomas S. Kuhn

exemplar, a very best and most instructive example.

Discovery comes not when something goes right but when something is awry, a novelty that runs counter to what was expected.

We have a tendency to see what we expect, even when it is not there. It often takes a long time for an anomaly to be seen for what it is, something contrary to the established order.

If one theory says the sentence is true and another says it is false, there is no contradiction, for the sentence expresses different statements in the two theories, and they cannot be compared.

“paradigms.” These I take to be universally recognized scientific achievements that for a time provide model problems and solutions to a community of practitioners.

historians confront growing difficulties in distinguishing the “scientific” component of past observation and belief from what their predecessors had readily labeled “error” and “superstition.”

If these out-of-date beliefs are to be called myths, then myths can be produced by the same sorts of methods and held for the same sorts of reasons that now lead to scientific knowledge.

If, on the other hand, they are to be called science, then science has included bodies of belief quite incompatible with the ones we hold today.

The extraordinary episodes in which that shift of professional commitments occurs are the ones known in this essay as scientific revolutions.

the tradition-shattering complements to the tradition-bound activity of normal science.

they can also be retrieved from the study of many other episodes that were not so obviously revolutionary.

there can be a sort of scientific research without paradigms,

In the absence of a paradigm or some candidate for paradigm, all of the facts that could possibly pertain to the development of a given science are likely to seem equally relevant.

early fact-gathering is a far more nearly random activity

a paradigm is rarely an object for replication.

it is an object for further articulation and specification under new or more stringent conditions.

Mopping-up operations are what engage most scientists throughout their careers.

normal science.

No part of the aim of normal science is to call forth new sorts of phenomena;

those that will not fit the box are often not seen at all.

has drastically restricted vision.

those restrictions, born from confidence in a paradigm, turn out to be essential to the development of science.

detail and depth

the range of anticipated, and thus of assimilable, results is always small compared with the range that imagination can conceive.

the project whose outcome does not fall in that narrower range is usually just a research failure, one which reflects not on nature but on the scientist.

Even the project whose goal is paradigm articulation does not aim at the unexpected novelty.

the conviction that, if only he is skilful enough, he will succeed in solving a puzzle that no one before has solved or solved so well.

That scientists do not usually ask or debate what makes a particular problem or solution legitimate tempts us to suppose that, at least intuitively, they know the answer. But it may only indicate that neither the question nor the answer is felt to be relevant to their research.

Normal science can proceed without rules only so long as the relevant scientific community accepts without question the particular problem-solutions already achieved.

Normal science does not aim at novelties of fact or theory and, when successful, finds none.

Discovery commences with the awareness of anomaly, i.e., with the recognition that nature has somehow violated the paradigm-induced expectations that govern 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 has become the expected.

consciously or not, the decision to employ a particular piece of apparatus and to use it in a particular way carries an assumption that only certain sorts of circumstances will arise.

Paradigm procedures and applications are as necessary to science as paradigm laws and theories, and they have the same effects. Inevitably they restrict the phenomenological field accessible for scientific investigation at any given time.

theory-induced.

during pre-paradigm periods and during the crises that lead to large-scale changes of paradigm, scientists usually develop many speculative and unarticulated theories that can themselves point the way to discovery. Often, however, that discovery is not quite the one anticipated by the speculative and tentative hypothesis.

Only as experiment and tentative theory are together articulated to a match does the discovery emerge and the theory become a paradigm.

novelty emerges only with difficulty, manifested by resistance, against a background provided by expectation.

Initially, only the anticipated and usual are experienced even under circumstances where anomaly is later to be observed.

Further acquaintance, however, does result in awareness of something wrong or does relate the effect to somet...

That awareness of anomaly opens a period in which conceptual categories are adjusted until the initially anoma...

At this point the discovery has be...

Without the special apparatus that is constructed mainly for anticipated functions, the results that lead ultimately to novelty could not occur.

even when the apparatus exists, novelty ordinarily emerges only for the man who, knowing with precision what he should expect, is able to recognize that something has gone wrong.

Anomaly appears only against the background provided by the paradigm. The more precise and far-reaching that paradigm is, the more sensitive an indicator it provides of anoma...

resistance guarantees that scientists will not be lightly distracted and that the anomalies that lead to paradigm change will penetrate existing knowledge to the core.

So long as the tools a paradigm supplies continue to prove capable of solving the problems it defines, science moves fastest and penetrates most deeply through confident employment of those tools.

retooling is an extravagance to be reserved for the occasion that demands it.

the act of judgment that leads scientists to reject a previously accepted theory is always based upon more than a comparison of that theory with the world.

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.

By themselves they cannot and will not falsify that philosophical theory, for its defenders will do what we have already seen scientists doing when confronted by anomaly. They will devise numerous articulations and ad hoc modifications of their theory in order to eliminate any apparent conflict.