 By recognizing Poincaré’s heritage as a structural point of view, Schlick insists on the conventional aspect of his structuralism. He sees in Poincaré’s conventions a third type of definition between the implicit definitions of the axiomatic method and the concrete or ostensive definitions of physical objects. These conventions are, as Friedman observes “crucial for an understanding of how we achieve a coordination between concepts and empirical reality in the mathematical exact sciences” (2007: 100). As Schlick explains: