The article addresses a characterization of the notion of case and in particular the nature of ergative case. We argue that the fundamental oblique case of natural languages (the genitive/dative) corresponds to an elementary inclusion or part-whole predicate, whose internal argument (the whole, or possessor) is the DP which the case embeds, while its external argument is a DP (the part or possessum) coinciding either with the head of a genitive construction or with the theme of a ditransitive verb.