  In “Logik und Erkenntnistheorie,” Schlick thought the most important component of languages are grammatical rules, which are of two kinds. First of all, there are ‘internal rules’, which govern the use of expressions in relation to other expressions, much like the formation and transformation rules of formal logic. In addition, Schlick conceived of a second type of grammatical rule, which he called ‘application-rules’ (Anwendungsregeln), regulating the use of expressions in connection with, or application to, observable extra-linguistic situations. Of course, application-rules govern not only descriptions of observable situations, but the use of indexicals and demonstratives as well, thus legitimizing Schlick’s affirmations by grounding them in grammar. And Schlick conceived grammar with sufficient breadth to encompass the natural languages of everyday life as well as the technical and highly regimented languages of science. Concurring with Carnap’s Principle of Tolerance, Schlick regarded the choice of grammatical rules, the choice of a particular grammar rather than an alternative, as conventional and therefore independent of extra-linguistic matters. And his endorsement of grammatical conventionalism was specifically intended to accommodate choices between languages which differed radically, as demonstrated in his treatment of philosophical pseudo-problems (Oberdan 1996, Sec. 3).