In can occur even where the conditional fact is known. The speaker may set aside the assumed certainty temporarily in order to draw attention to the consequence that follows from the assumption.
إِنْ كَانَ أَبُوكَ فَلَا تُؤْذِهِ
If he is your father, do not hurt him.
This need not question a known relationship. The assumption can reproach the addressee or demand behavior consistent with the fact. It illustrates rhetorical reframing rather than actual doubt.
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Conditional Particles: In, Idha, Law, and Rhetorical Reframing
In can occur even where the conditional fact is known. The speaker may set aside the assumed certainty temporarily in order to draw attention to the consequence that follows from the assumption.
إِنْ كَانَ أَبُوكَ فَلَا تُؤْذِهِ
If he is your father, do not hurt him.
This need not question a known relationship. The assumption can reproach the addressee or demand behavior consistent with the fact. It illustrates rhetorical reframing rather than actual doubt.