The first rule after the chart notes that verbal nouns naming crafts and occupations are frequently built on فَعَالَةٌ or فِعَالَةٌ.
دِبَاغَةٌ — حَجَامَةٌ — حِيَاكَةٌ — خِيَاطَةٌ — كِتَابَةٌ
Translation: tanning, barbering/cupping, weaving, sewing, writing.
The qualifier frequently matters: it describes a strong tendency, not an exceptionless law for all occupational nouns.
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Occupational / Craft Maṣdars
Noun Patterns: Jāmid, Maṣdar, Mushtaq and 50 Basic-Triliteral Maṣdar Entries
The first rule after the chart notes that verbal nouns naming crafts and occupations are frequently built on فَعَالَةٌ or فِعَالَةٌ.
دِبَاغَةٌ — حَجَامَةٌ — حِيَاكَةٌ — خِيَاطَةٌ — كِتَابَةٌ
Translation: tanning, barbering/cupping, weaving, sewing, writing.
The qualifier frequently matters: it describes a strong tendency, not an exceptionless law for all occupational nouns.