Cases, however, are marked in the Qur'an, children's books, and to remove ambiguous situations.
Grammatical case endings are not pronounced in pausa and in less formal forms of Arabic.
The dual and regular masculine plural are formed by adding ـَانِ -an(i) and ـُونَ -ūn(a) respectively (just ـَا -ā and ـُو -ū in the construct state).
The regular feminine plural is formed by adding ـَاتِ -āt(i) in the definite and -āt(in) in the indefinite (spelled identically).
The regular feminine plural is formed by adding ـَاتِ -āt(i) in the definite and ـَاتٍ -āt(in) in the indefinite (spelled identically in Arabic).
For fully declined nouns, known as "triptote" (مُنْصَرِفٌ munṣarif), that is, having three separate case endings, the suffixes are -u, -a, -i for nominative, accusative, and genitive case respectively, with the addition of a final /n/ (nunation, or tanwīn) to produce -un, -an, and -in when the word is indefinite.
It also applies to feminine nouns ending in ة -a/-at (tā’ marbūṭah) and ء hamzah, but for these, ا alif is not written in the accusative case.
The genitive reverts to the normal -i when the diptotic noun becomes definite (preceded by al- or is in the construct state)).
In the case of sound masculine plurals (جَمْعُ ٱلْمُذَكَّرُ ٱلسَّالِمُ - jam‘ al-mudhakkar as-sālim), mostly denoting male human beings, the suffixes are respectively ـُونَ -ūna and ـِينَ -īna.
In the case of sound feminine plurals (جَمْعُ ٱلْمُؤَنَّثُ ٱلسَّالِمُ jam‘ al-mu’annath as-sālim), the suffixes are respectively ـَاتٌ, ـَاتُ -ātu(n), ـَاتٍ, ـَاتِ -āti(n) and ـَاتٍ, ـَاتِ -āti(n) (identical spelling).
Again the final vowel is dropped in speech and pausa, leaving only ـَات -āt, making all cases pronounced identically.
They decline very similarly to the sound masculine plurals because they are not marked for definiteness and look the same in both the accusative and genitive cases.
These nouns were reckoned by the grammarians to have originally taken the triptotic endings, but through morpho-phonotactic processes, the latter resulted.
Also, a noun can be both ism al-manqūṣ and diptotal: for example, layālin 'nights', is a broken plural with a final unstable vowel.
ٱسْمُ ٱلْمَقْصُورِ ism al-maqṣūr (deficient nouns ending with alif or alif maqṣūrah) - These nouns, like their close relative ism al-manqūṣ, also behave differently due to the instability of a final vowel.
These nouns are marked only for definiteness, as morpho-phonotactic processes have resulted in the complete loss of the case distinctions.
An example of a common invariable noun is fuṣḥá (al-fuṣḥá), meaning 'the most eloquent [Arabic]'.
Such a sentence using the particle إِنَّ ("Verily, this writer wrote the book") would be formed as follows (read from right to left): Although there was an overt verb in the above example, a nominal sentence without an overt verb will also have its subject take accusative case because of the introduction of one of inna's sisters.
Traditional Arab grammarians equated the indicative with the nominative of nouns, the subjunctive with the accusative, and the jussive with the genitive, as indicated by their names (the only pair that is not borne out in the name is the jussive-genitive pair, probably because the -i vowel is usually dropped).
It is not known whether there is a genuine historical connection or whether the resemblance is mere coincidence, caused by the fact that these are the only three short vowels available.