The essay re-examines the detailed arguments by Ludwik Antoni Birkenmajer (1855–1929) and Curtis Wilson (1921–2012) about how Copernicus’s rejection of Ptolemy’s solution to the problem of the non-uniform motions of the planets and the Moon led him to his first version of the heliocentric theory. The essay then acknowledges the speculative character of their reconstructions, the problem of anachronism in both accounts, and the mistakes that Copernicus himself made. By following their basic insights, however, readers can understand how the inconsistency in Ptolemy’s preservation of the axiom of uniform motion motivated Copernicus – first, to seek an alternative solution, and, second, to question eccentrics, which, in turn, led him to investigate epicycles. The concluding section complements their accounts, leading to an original interpretation of Copernicus’s reliance on medieval Polish developments in dialectical reasoning and on a comment in one of the books (now at Uppsala) that he annotated to develop his new vision and to construct the postulates near the beginning of Commentariolus (ca. 1510).

The essay re-examines the detailed arguments by Ludwik Antoni Birkenmajer (1855–1929) and Curtis Wilson (1921–2012) about how Copernicus’s rejection of Ptolemy’s solution to the problem of the non-uniform motions of the planets and the Moon led him to his first version of the heliocentric theory. The essay then acknowledges the speculative character of their reconstructions, the problem of anachronism in both accounts, and the mistakes that Copernicus himself made. By following their basic insights, however, readers can understand how the inconsistency in Ptolemy’s preservation of the axiom of uniform motion motivated Copernicus – first, to seek an alternative solution, and, second, to question eccentrics, which, in turn, led him to investigate epicycles. The concluding section complements their accounts, leading to an original interpretation of Copernicus’s reliance on medieval Polish developments in dialectical reasoning and on a comment in one of the books (now at Uppsala) that he annotated to develop his new vision and to construct the postulates near the beginning of Commentariolus (ca. 1510).