 According to Schlick, Poincaré’s conventions combine conceptual definitions and coordinations. Given the fact that both expressions are completely foreign to Poincaré’s style, how should one understand Schlick’s claim? In fact, Schlick’s expressions designate two different aspects of Poincaré’s structural approach, which pay attention to the fact that Poincaré is not an ante rem structuralist (the ante rem structuralist takes the pattern to exist independently of any systems that exemplify it). At first glance he seems to be an ontological realist with respect to relational universals (but not with respect to individuals (relata)), despite his predicativist attitude. As Elie Zahar emphasizes, such a position is not naturally compatible with classical semantics (logic) because this latter “seems unable to interpret relations except through their relata”: one cannot confirm \(R(a,b)\) without determining