● Let us carefully compare rational and non-rational nouns as we change singular nouns into dual and plural forms:
Singular sentenceDual sentencePlural sentence (with rational/non-rational rule)
هٰذَا مُسْلِمٌهٰذَانِ مُسْلِمَانِهٰؤُلَاءِ مُسْلِمُونَ (rational masculine plural)
هٰذِهِ مُسْلِمَةٌهَاتَانِ مُسْلِمَتَانِهٰؤُلَاءِ مُسْلِمَاتٌ (rational feminine plural)
ذٰلِكَ مُهَنْدِسٌذَانِكَ مُهَنْدِسَانِأُولٰئِكَ مُهَنْدِسُونَ (rational masculine plural)
تِلْكَ مُهَنْدِسَةٌتَانِكَ مُهَنْدِسَتَانِأُولٰئِكَ مُهَنْدِسَاتٌ (rational feminine plural)
هٰذَا كِتَابٌهٰذَانِ كِتَابَانِهٰذِهِ كُتُبٌ (non-rational plural: feminine singular demonstrative)
هٰذَا قَلَمٌهٰذَانِ قَلَمَانِهٰذِهِ أَقْلَامٌ (non-rational plural: feminine singular demonstrative)
هٰذِهِ كُرَّاسَةٌهَاتَانِ كُرَّاسَتَانِهٰذِهِ كُرَّاسَاتٌ (non-rational plural: feminine singular demonstrative)