Equivalence of Hypotheses and Relativity of Motion in the “Dynamica”

Abstract

Leibniz’s conception of the relativity of motion has been discussed at length for a very long time. This paper doesn’t aim to give a full solution to this question, but to contribute to the debate by clarifying how the principle of relativity is introduced, justified and used in the “Dynamica”. Four different principles are identified : one purely geometrical, and three (meta) physical principles, which express God’s wisdom : a principle of equivalence of hypotheses linked to the action/reaction principle, a Galilean principle of relativity and a general principle which apply not only to rectilinear motions but also to circular ones. I argue that to appreciate the coherence of Leibniz’ approach, we should distinguish these principles more sharply than he himself did and pay more attention to their status : are they consequences of the definition of motion, consequences of the physical laws or necessary conditions for any physical theory?