An attached subject pronoun is a short bound form inside the verb. Reinforcing it with a separate form makes the intended coordinate relation explicit.
In ضَرَبْتُ أَنَا وَزَيْدٌ, anā signals that Zayd is coordinated with the subject -tu.
This particular rule concerns an attached nominative pronoun, not every overt subject noun.
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Coordination (ʿAṭf bi-l-Ḥurūf): Rules and Parsing
An attached subject pronoun is a short bound form inside the verb. Reinforcing it with a separate form makes the intended coordinate relation explicit.
In ضَرَبْتُ أَنَا وَزَيْدٌ, anā signals that Zayd is coordinated with the subject -tu.
This particular rule concerns an attached nominative pronoun, not every overt subject noun.