There is no universal point of view as to the case system in English. Different scholars stick to a different number of cases.
1. There are two cases. (limited case theory) The Common one and The Genitive;
2. There are no cases at all, the form `s is optional because the same relations may be expressed by the ‘of-phrase’: the doctor’s arrival – the arrival of the doctor;
3. There are three cases: the Nominative, the Genitive, the Objective due to the existence of objective pronouns me, him, whom;
4. The theory of positional cases.
5. The theory of prepositional cases.