Case marking has long resisted rationalization in terms of language-external systems of cognition, representing a classical illustration in the generative tradition for an apparently purely 'formal' or 'syntactic' aspect of grammatical organization. I argue that this impasse derives from the prevailing absence of a notion of grammatical meaning, i.e. meaning unavailable lexically or in non-linguistic cognition and uniquely dependent on grammatical forms of organization. In particular, propositional forms of reference, contrary to their widespread designation as 'semantic', are arguably not only grammar-dependent but depend on relations designated as structural 'Cases'. I further argue that these fail to reduce to thematic structure, Person, Tense, or Agreement. Therefore, Case receives a rationalization in terms of how lexical memory is made referential and propositional in language. Structural Case is 'uninterpretable' (bereft of content) only if a non-grammatical notion of meaning is employed, and sapiens-specific cognition is (implausibly) regarded as unmediated by language.