A plea for a correct translation of Newton’s law of inertia

Abstract

The formulations of Newton’s law of inertia in university-level textbooks usually follow the Motte–Cajori translation of Newton’s Principia. The rich content of Newton’s law of inertia as a causality principle for mechanics is partly hidden by Motte’s mistranslation of the Latin phrase nisi quatenus as unless instead of except insofar as. One effect of this error is a tendency to isolate from the law some of the ‘‘Definitions’’ that precede Newton’s statement of the three laws of motion. These definitions, when taken together with the laws, provide the basis for Newton’s quantitative and qualitative elaboration of the coupled concepts of mass and force.