There are three cases in English: the Nominative, the Possessive, and the Objective.
The NOMINATIVE CASE; the form used in address and as the subject of a verb.
The OBJECTIVE CASE; the form used as the object of a verb or a preposition. It is always the same in form as is the nominative.
Since no error in grammar can arise in the use of the nominative or the objective cases of nouns, no further discussion of these cases is here needed.
The POSSESSIVE CASE; the form used to show ownership. In the forming of this case we have inflection.