Ilm-ul-Nahv(نحو )
The concept of Grammatical States is the cornerstone of Ilm-ul-Nahv نحو . Without the proper understanding of grammatical states, you can end up saying The rat ate the cat when you want to say The cat ate the rat. An oft-cited example for this is from the Quran:
وَإِذِ ابْتَلَىٰ إِبْرَاهِيمَ رَبُّهُ
“And remember when the Lord of Ibrahim tested him…” (Al-Baqarah: 124)
Notice the fatha at the end of ﺍإِبْرَاهِيمَ and the dhamma at the end of رَبُّهُ(…Ibrahima Rabbuhu…). Now if someone was to say the same thing as (…Ibrahimu Rabbahu…), that is, switch the fatha with the dhamma, that would mean “Ibrahim tested his Lord”, which would change the meaning altogether