فَـ«أَسْوَدُ» وَ«أَرْقَمُ» غَيْرُ مُنْصَرِفٍ، وَإِنْ صَارَا اسْمَيْنِ لِلْحَيَّةِ؛ لِأَصَالَتِهِمَا فِي الْوَصْفِيَّةِ.
Translation: Thus, aswad and arqam are diptotes even if they have become names for a snake, because they were originally adjectival.
The book highlights the persistence of original adjectival status. Their morphological verb-like pattern also matters when explaining the effective combination of causes.