Inflection of Arabic Nouns

Triptotes (ordinary declinable nouns) mark case with a short vowel: ḍamma for nominative, faṭḥa for accusative, kasra for genitive. When indefinite, they also take nunation.

Diptotes never take nunation. When indefinite, they take a faṭḥa for both accusative and genitive. When definite, they behave like triptotes.

A group of words called the “five nouns” behave like triptotes, but mark case with a long vowel when they are muḍāf (the possessor in an iḍāfa). There are actually six of these: أَب، أَخ، حَم، ذُو، فُو، هَن (but هَن is rare).

Nouns ending in yāʼ behave like triptotes in the accusative. In the nominative and genitive, they lose their final yāʼ and replace it with a double kasra when indefinite; they keep the yāʼ with no short vowel when definite.

Nouns ending in alif maqṣūra do not change with case at all. When indefinite, they take a double faṭḥa on the alif maqṣūra.

Dual nouns end in ـانِ in the nominative, and ـَينِ in the accusative and genitive. When muḍāf, they lose the final نِ.

Sound masculine plurals end in ـُونَ in the nominative, and ـِينَ in the accusative and genitive. Likewise, they lose the final نَ when muḍāf.

Sound feminine plurals behave like triptotes, but take a kasra for both accusative and genitive.

Finally, some nouns are indeclinable and do not mark case at all.

Note: a double faṭḥa can only be written on an alif, alif maqṣūra, hamza or tāʼ marbūṭa. Otherwise, an alif must be added as a seat for the short vowel.