إِلَّا «اثْنَيْ عَشَرَ»، فَإِنَّهَا مُعْرَبَةٌ كَالْمُثَنَّى
Translation: Except “twelve”, which is declined like the dual.
To unpack the book’s concise statement, separate the components: اثنا/اثني changes like a dual, whereas عَشَرَ remains fixed on fatḥ. The whole expression is therefore not described by exactly the same “both parts fixed” rule as the other compound numerals.
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Al-Murakkabāt — Compound Numerals, the Twelve Exception and Declining Baalbek
إِلَّا «اثْنَيْ عَشَرَ»، فَإِنَّهَا مُعْرَبَةٌ كَالْمُثَنَّى
Translation: Except “twelve”, which is declined like the dual.
To unpack the book’s concise statement, separate the components: اثنا/اثني changes like a dual, whereas عَشَرَ remains fixed on fatḥ. The whole expression is therefore not described by exactly the same “both parts fixed” rule as the other compound numerals.