Boris Hessen’s ‘The Social and Economic Roots of Newton’s Principia’ (see https://doi.org./10.1163/1569206X-00002041) is considered a pioneering work in the historiography of the natural sciences. For some, it marks the founding moment of the ‘externalist’ approach to this field of study. Previously, Hessen published another paper on Newton entitled ‘Preface to Articles by A. Einstein and J.J. Thomson’, which, some maintain, bears a stronger resemblance to works in the ‘internalist’ camp of the historiography of the natural sciences. For decades, scholars have (...) puzzled over why Hessen chose to argue for, seemingly, diametrically opposed positions. In this paper, however, I argue that Hessen does not advance two different historiographical methods, but a single, dialectical-materialist approach that accounts for the ‘unity in opposition’ of the external and internal dimensions of natural-scientific theory. I draw from Hessen’s two papers on Newton, his previously untranslated writings, as well as selections from the secondary literature. (shrink)