1. The book defines the declinable noun through grammatical construction and the absence of resemblance to inherently fixed forms.
2. «زَيْدٌ» in «قَامَ زَيْدٌ» is a declinable noun and nominative subject.
3. «هَؤُلَاءِ» in «قَامَ هَؤُلَاءِ» is indeclinable, though in the nominative position as subject.
4. Another term for the declinable noun is mutamakkin.
Next level: changes in the word ending and visible versus estimated case marking.