Under the category of case we understand the change of form of a noun to denote its grammatical relations to other parts of communication.
The number of cases varies in different languages { two in English (common and Genitive), 7 (including the Vocative case) in Russian). It depends upon the morphological structure of the language and its development.
In Old English cases corresponded to the syntactical positions of nouns. The Nominative represented a subject or a predicative, the Accusative represented direct object, the Dative stood for a indirect object, the Genitive stood for an attribute, the Vocative denoted a direct address. In the course of time the number of cases got reduced , the inflexions died out, and the relations of nouns to other parts of communication came to be expressed by word order, prepositions and two cases – the Common and the Genitive.