Thomas Kuhn used the word ‘incommensurable’ to indicate the fundamental differences between pre- and post-revolutionary paradigms, but he was also much intrigued about why the natural sciences differ from other academic subjects in act consensually in times of normal science. This chapter proposes that impersonal methods of assessing weight, measure, and currency, which were fundamental for establishing commensurable norms in marketplaces, provided the foundation for considering how to apply material commensurability to a knowledge of natural kinds. Once material sameness is defined and accepted, it disappears from the group of issues that are contested. The narrowly focused but powerful activities in biomedicine show how important material commensurability is for creating a scientific field that can include anyone, anywhere. Historical examples are introduced to show how an understanding of medicinal substances (‘drugs’) shifted from personal qualitative experience to impersonal materialistic experiment. The power to materially define and to extract or manufacture globally understood substances illuminates a widely understood version of progress of medicine. Its deep roots in market exchange also point to the limits of biomedicine to better the health of humans without other forms of governance.