فَهَذِهِ الْحُرُوفُ تَدْخُلُ عَلَى الْمُبْتَدَإِ وَالْخَبَرِ، فَتَنْصِبُ الْمُبْتَدَأَ وَيُسَمَّى اسْمَ «إِنَّ»، وَتَرْفَعُ الْخَبَرَ وَيُسَمَّى خَبَرَ «إِنَّ».
Translation: These particles enter a mubtadaʾ–khabar construction. They make the original subject accusative, now called the ism of inna, and keep the predicate nominative, now called its khabar.
The ism of inna is accusative, while its khabar is nominative. «إِنَّ» itself is an indeclinable particle, neither noun nor verb.