co-ordinative definitions

Term used by the German-born American philosopher of science Hans Reichenbach (1891–1953), in The Philosophy of Space and Time (1957), for the co-ordination of a concept of physical theory with an actual physical process. For example, the metre may be co-ordinated with a standard rod in Paris, or in geometry a straight line may be co-ordinated with the path of a light ray, or the path of a light ray in a certain kind of space. Reichenbach thought that since there is no way of knowing whether objects maintain their size when transported to different regions of space, the assumption that they do takes on the status of a convention or definition, and is part of what co-ordinates the concepts with which we measure space with physical space itself.