There are two kinds. In actual transformation (عدلِ تحقیقی), the original expression is known, such as مَثْنَىٰ from اِثْنَانِ اِثْنَانِ. In assumed transformation (عدلِ تقدیری), grammarians treat the form as changed from an assumed original, such as عُمَرُ from عَامِرٌ.
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Two Kinds of Transformation
Cause of Ghayr Munsarif: Transformation (Adl)
There are two kinds. In actual transformation (عدلِ تحقیقی), the original expression is known, such as مَثْنَىٰ from اِثْنَانِ اِثْنَانِ. In assumed transformation (عدلِ تقدیری), grammarians treat the form as changed from an assumed original, such as عُمَرُ from عَامِرٌ.