Without an expressed lām, taʾdīban is accusative, while lām is understood semantically.
With overt lām, at-taʾdībi becomes genitive.
The explanatory “understood lām” expresses the causal relationship; do not parse the accusative noun as though an actual written preposition governed it.
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Al-Mafʿūl Lahu: Expressing the Reason for an Action
Without an expressed lām, taʾdīban is accusative, while lām is understood semantically.
With overt lām, at-taʾdībi becomes genitive.
The explanatory “understood lām” expresses the causal relationship; do not parse the accusative noun as though an actual written preposition governed it.