What is scientific revolutions?

Thomas Kuhn, answered from the texts and cited to the page.

Thomas Kuhn answers

Scientific revolutions are those non-cumulative developmental episodes in which an older paradigm is replaced in whole or in part by an incompatible new one.¹ The path to revolution runs through crisis. When an anomaly resists solution long enough, more and more of a field's most eminent practitioners come to regard its resolution as the central problem of their discipline — and at that point the field no longer looks quite the same as it had.²

The early attacks on the resistant problem follow paradigm rules closely; but with continuing resistance, the attacks multiply into divergent articulations, increasingly described as ad hoc adjustments, until the rules of normal science become blurred and even formerly standard solutions are called into question.³ The symptoms of this transition are recognizable: a proliferation of competing articulations, willingness to try anything, explicit discontent, recourse to philosophy and debate over fundamentals.⁴

What revolution then effects is not merely a correction of mistakes but a restructuring of the concepts by which terms attach to nature. The Copernican case is the clean illustration: before the transition, the sun and moon were planets and the earth was not; after it, the earth was a planet, the sun a star, the moon a new kind of body, a satellite.⁵

These were not additions to existing knowledge. One cannot get from the old to the new simply by accumulation, nor describe the new in the vocabulary of the old — the compound sentence "In the Ptolemaic system planets revolve about the earth; in the Copernican they revolve about the sun" is, strictly construed, incoherent, because the two occurrences of planet attach to nature differently.⁶

The late work pushed this picture further. I came to see revolutions less as the replacement of one paradigm by another and more as a speciation event: an old way of doing science splinters into newly formed specialties, each developing its own complete structured lexicon, incommensurable not only with the old framework but with the lexicons of the other new disciplines as well.⁷

Incommensurability, on this picture, is not a temporary embarrassment to be overcome by better translation; it is a structural feature of how scientific knowledge differentiates over time.

Sources

1. scientific revolutions are here taken to be those non-cumulative developmental episodes in which an older paradigm is replaced in whole or in part by an incompatible new one.

   The Structure of Scientific Revolutions, pp. 77–79

2. If it still continues to resist, as it usually does not, many of them may come to view its resolution as the subject matter of their discipline. For them the field will no longer look quite the same as it had earlier.

   The Structure of Scientific Revolutions, p. 72

3. Through this proliferation of divergent articulations (more and more frequently they will come to be described as ad hoc adjustments), the rules of normal science become increasingly blurred.

   The Structure of Scientific Revolutions, p. 72

4. The proliferation of competing articulations, the willingness to try anything, the expression of explicit discontent, the recourse to philosophy and to debate over fundamentals, all these are symptoms of a transition from normal to extraordinary research.

   The Structure of Scientific Revolutions, pp. 77–79

5. Before it occurred, the sun and moon were planets, the earth was not. After it, the earth was a planet, like Mars and Jupiter; the sun was a star; and the moon was a new sort of body, a satellite.

   The Road Since Structure, p. 22

6. Consider the compound sentence, 'In the Ptolemaic system planets revolve about the earth; in the Copernican they revolve about the sun.' Strictly construed, that sentence is incoherent. The first occurrence of the term 'planet' is Ptolemaic, the second Copernican, and the two attach to nature differently.

   The Road Since Structure, p. 22

7. He no longer identified scientific revolutions as periods in which a new paradigm replaces an old one, but rather, he saw them as periods in which an old way of doing science effectively splinters into a number of newly formed specialties... each will develop what Kuhn came to call a complete structured lexicon, incommensurable with the structured lexicons of the other disciplines.

   The Last Writings, pp. 27–28