In this paper, we argue for an approach to grammatical case that treats case-marking not as the passive realisation of other morpho-syntactic properties of a construction, but as bringing its own independent contribution to the construal of a clause, through inference over possibly underspecified semantic content of a case-marker in context. We take as case studies two instances of Differential Case-Marking: the partitive alternation in Estonian and differential uses of the marker ko in Hindi/Urdu. For Estonian, it is argued that the partitive case is semantically partitive even in alternation in grammatical contexts with nominative and genitive. From this assumption, we derive the various construals of the partitive as indicating indefinite quantity or imperfective aspect and show how other uses of the case, including after negation, may be traced to the basic partitive interpretation. We also argue that the completive interpretations of nominative and genitive derive from contrast with the partitive reading, rather than as being encoded in the case marking itself. With Hindi/Urdu ‘dative’ maker ko, we argue how pragmatic inference can operate also over grammatical levels to explain the uses of the marker with human direct objects, to specify definiteness of inanimate direct objects and, in alternation with ergative ne, deontic modality.