وَلِأَنَّهُ فِي الْمَعْنَى عِبَارَةٌ عَنْهُ
And because in meaning it represents that very subject.
In «زَيْدٌ هُوَ الْقَائِمُ», «huwa» does not introduce a second, absent person. In sense it points back to Zayd, so the separating pronoun should not be understood as semantically independent of the musnad ilayh.
If «huwa» were made to refer to another person, the relation would no longer be the same construction analyzed here.
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The Separating Pronoun (Ḍamīr al-Faṣl): Restriction, Emphasis and Predication
وَلِأَنَّهُ فِي الْمَعْنَى عِبَارَةٌ عَنْهُ
And because in meaning it represents that very subject.
In «زَيْدٌ هُوَ الْقَائِمُ», «huwa» does not introduce a second, absent person. In sense it points back to Zayd, so the separating pronoun should not be understood as semantically independent of the musnad ilayh.
If «huwa» were made to refer to another person, the relation would no longer be the same construction analyzed here.