  Schlick also contributed a critical essay on Ernst Cassirer’s 1921 work on Einstein’s Theory of Relativity to the prestigious journal Kant-Studien (Cassirer 1921; Schlick 1979a, 322–334). In “Critical or Empiricist Interpretation of Modern Physics?” of 1921, Schlick explained that Cassirer’s argument rested on a false dichotomy. On the one hand, Cassirer’s own Logical Idealism incorporates principles for the ordering and measuring of sensations to constitute physical objects. On the other hand, the only alternative Cassirer considered is a variety of phenomenalistic empiricism founded on “the sensualistic concept of experience”. In other words, Cassirer’s operative assumption is simply that the only possible philosophical frameworks for understanding contemporary science are a strict empiricism or one incorporating constitutive principles. Of course, Schlick regarded his own philosophical framework as a clear counterexample, since it is an empiricist epistemology distinguished by its inclusion of constitutive principles. Thus, Cassirer committed the same error as Reichenbach by blithely ignoring the possibility of constitutive principles which are not synthetic apriori judgments.  Naturally, a combination of empiricism with constitutive principles would fall somewhere between the strict empiricism Cassirer refutes and the Logical Idealism Cassirer defends. At this point, Schlick first used what would eventually become a familiar complaint against Kant and the neo-Kantians among Logical Positivists, especially their characterization of the constitutive principles as synthetic judgments apriori. As Schlick understood constitutive principles, they are certainly not synthetic apriori principles, for they are conventions, which are neither apriori nor synthetic (Schlick 1979a, 322–334). The result of Schlick’s critique was, in Einstein’s words, “truly inspirational” (Einstein 1921).