Osiander’s Epistemology of Astronomy

Abstract

Andreas Osiander’s Ad lectorem, attached to Copernicus’ De revolutionibus, had for long been considered a classical expression of the instrumentalist view of science. The main point of this short anonymous text is that Copernicus’ thesis (i.e. that “the earth moves while the sun is at rest in the center of the universe”) is, like all other astronomical models, only a mathematical “hypothesis”, which enables the calculation of the positions of heavenly bodies but does not reflect the physical reality of the universe. The author puts Osiander’s text in the context of the standard 16th century epistemological demands for scientific explanation and argues that Osiander is not an instrumentalist in the modern sense of the term. Osiander’s epistemology of astronomy is not the result of the instrumentalist view of science in general, but a reflection of the astronomer’s impossibility to decide – on the basis of observations from the earth – which models of the real heavenly spheres present the actual causes of the movement of the heavenly bodies.