According to the conventionalist doctrine of space elaborated by the French philosopher-scientist Henri Poincaré in the 1890s, the geometry of physical space is a matter of definition, not of fact. Poincaré's Hertz-inspired view of the role of hypothesis in science guided his interpretation of the theory of relativity (1905), which he found to be in violation of the axiom of free mobility of invariable solids. In a quixotic effort to save the Euclidean geometry that relied on this axiom, Poincaré extended (...) the purview of his doctrine of space to cover both space and time. The centerpiece of this new doctrine is what he called the "principle of physical relativity," which holds the laws of mechanics to be covariant with respect to a certain group of transformations. For Poincaré, the invariance group of classical mechanics defined physical space and time (Galilei spacetime), but he admitted that one could also define physical space and time in virtue of the invariance group of relativistic mechanics (Minkowski spacetime). Either way, physical space and time are the result of a convention. (shrink)

This paper offers an interpretation of Poincaré's conventionalism, distinguishing it from the Duhem–Quine thesis, on the one hand, and, on the other, from the logical positivist understanding of conventionalism as a general account of necessary truth. It also confronts Poincaré's conventionalism with some counter-arguments that have been influential: Einstein's (general) relativistic argument, and the linguistic rejoinders of Quine and Davidson. In the first section, the distinct roles played by the inter-translatability of different geometries, the inaccessibility of space to direct observation, (...) and general holistic considerations are identified. Together, they form a constructive argument for conventionalism that underscores the impact of fact on convention. The second section traces Poincaré's influence on the general theory of relativity and Einstein's ensuing ambivalence toward Poincaré. Lastly, it is argued that neither Quine nor Davidson has met the conventionalist challenge. (shrink)

According to the conventionalist doctrine of space elaborated by the French philosopher-scientist Henri Poincaré in the 1890s, the geometry of physical space is a matter of definition, not of fact. Poincaré’s Hertz-inspired view of the role of hypothesis in science guided his interpretation of the theory of relativity (1905), which he found to be in violation of the axiom of free mobility of invariable solids. In a quixotic effort to save the Euclidean geometry that relied on this axiom, Poincaré extended (...) the purview of his doctrine of space to cover both space and time. The centerpiece of this new doctrine is what he called the ‘‘principle of physical relativity,’’ which holds the laws of mechanics to be covariant with respect to a certain group of transformations. For Poincaré, the invariance group of classical mechanics defined physical space and time (Galilei spacetime), but he admitted that one could also define physical space and time in virtue of the invariance group of relativistic mechanics (Minkowski spacetime). Either way, physical space and time are the result of a convention. (shrink)