أَغْلَقْتُ الْبَابَ خَوْفًا: al-bāba is the direct object and khawfan the reason complement.
The object answers “what was closed?”; the reason answers “why was it closed?”.
Both may be accusative in one sentence but perform different functions.
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Direct Object versus Reason Complement
Al-Mafʿūl Lahu: Expressing the Reason for an Action
أَغْلَقْتُ الْبَابَ خَوْفًا: al-bāba is the direct object and khawfan the reason complement.
The object answers “what was closed?”; the reason answers “why was it closed?”.
Both may be accusative in one sentence but perform different functions.