The former object receives a new grammatical role.
In شُرِبَ الْمَاءُ, الْمَاءُ is no longer an accusative object. It is the نائب الفاعل, and its grammatical case is nominative. Another descriptive term is مفعول ما لم يُسَمَّ فاعلُهُ: the receiver whose doer was not named.
Simple examples:
● فُتِحَ الْبَابُ — The door was opened.
● كُتِبَ الدَّرْسُ — The lesson was written.
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The former object receives a new grammatical role.
In شُرِبَ الْمَاءُ, الْمَاءُ is no longer an accusative object. It is the نائب الفاعل, and its grammatical case is nominative. Another descriptive term is مفعول ما لم يُسَمَّ فاعلُهُ: the receiver whose doer was not named.
Simple examples:
● فُتِحَ الْبَابُ — The door was opened.
● كُتِبَ الدَّرْسُ — The lesson was written.