Copernicus saw as counter instances what most of Ptolemy's other successors had seen as puzzles in the match between observation and theory. Anomalies are usually not considered counter-instances but rather simply puzzles. New paradigms come from people new to the field or young or both. Once it has achieved the status of a paradigm a scientific theory is declared invalid only if an alternative candidate is available to take its place. Scientific revolutions are inaugurated by a growing sense, again often restricted to a narrow subdivision of the scientific community that an existing paradigm has ceased to function adequately in the exploration of an aspect of nature to which the paradigm itself had previously led the
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