The Structure of Scientific Revolutions

'Normal science,' in Kuhn's framework, is puzzle-solving within an accepted paradigm — a shared set of assumptions, methods, and exemplary solved problems that a scientific community treats as settled foundations, not open questions. Anomalies — observations that don't fit the paradigm — accumulate slowly and are usually explained away or set aside rather than treated as immediately fatal to the paradigm. A genuine crisis emerges only when anomalies accumulate past a threshold, and a paradigm shift happens when a new framework emerges that resolves the anomalies by reorganizing the field's basic assumptions, not just adding new facts to the old ones — the switch from Ptolemaic to Copernican astronomy, or Newtonian to Einsteinian physics, are Kuhn's central examples. Crucially, Kuhn argued paradigms are often incommensurable — practitioners on either side of a shift can partly talk past each other, because the shift changes what counts as a relevant fact or a good explanation in the first place, not just which specific claims are believed true.