Kepler and the origins of pre-Newtonian mass

Abstract

The technical concept of “mass” is traced from its medieval origins in theology up to, but not including, Newton's Principia. Building on the advances of the Middle Ages, Kepler conceived, albeit in rudimentary form, the fundamental physical ideas of mass, “inertia,” and gravitational “mutual attraction.” These splendid concepts were later developed and carried forward into Newton's era by several 17th-century natural philosophers. Unlike his three planetary laws, Kepler's physics has long gone unappreciated by the scientific community. Nonetheless, it formed the conceptual foundation for much of classical dynamics.