When أَبٌ، أَخٌ، حَمٌ، or فَمٌ is added to ياء المتكلم (“my”), the same surface form remains in all three case roles. With أَبٌ:
جَاءَ أَبِي — my father came.
رَأَيْتُ أَبِي — I saw my father.
مَرَرْتُ بِأَبِي — I passed by my father.
The case role has not disappeared; only the visible form stays أَبِي.
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The Five Nouns: Core Case Forms
When أَبٌ، أَخٌ، حَمٌ، or فَمٌ is added to ياء المتكلم (“my”), the same surface form remains in all three case roles. With أَبٌ:
جَاءَ أَبِي — my father came.
رَأَيْتُ أَبِي — I saw my father.
مَرَرْتُ بِأَبِي — I passed by my father.
The case role has not disappeared; only the visible form stays أَبِي.