The Arabic Language

ʾaḥmaru 
‘red’, 
genitive/accusative 
ʾaḥmara
, do not have nunation and lose the genitive ending. 
When they become definite, they return to the triptotic declension, for example, 
al-ʾaḥmaru
, 
al-ʾaḥmari
, 
al-ʾaḥmara
. For the Arabic grammarians, explaining why 
some nouns lose part of their declension was an important task of morphology. 
Diptotic nouns are called in Arabic 
ġayr munṣarif
‘not free to move’, since they 
lack part of the alterability that is inherent in nouns. According to the Arabic 
grammarians, the main principle is that if a noun deviates from the unmarked 

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The Arabic Language
(i.e., singular, masculine, indefinite) state in more than one way, it resembles 
a verb and therefore loses part of its declensional rights. These deviations are 
the so-called 
mawāniʿ aṣ-ṣarf
‘the preventing factors of complete declension’, for 
instance, when a noun is definite, plural, feminine, a proper name, of foreign 
origin, an epithet or when it has a verbal pattern. On this basis, words like 
yazīdu
‘Yazīd’ (name, verbal pattern), 
ʾibrāhīmu
‘Abraham’ (name, foreign origin) and the 
comparative 
ʾafʿalu
(epithet, verbal pattern) are assigned to the category of the 
diptotic nouns.
In Arabic grammatical theory, diptotic nouns are fundamentally different from 
nouns that in their surface form do not exhibit all case endings. This occurs in 
the so-called weak nouns, that is, nouns containing one of the glides 
w
, 
y
or 
ʾalif
. 
In these nouns, phonological rules may produce a merger of case endings, for 
example, 
qāḍin
‘judge’, with genitive 
qāḍin
, accusative 
qāḍiyan
; or 
ʾafʿan
‘viper’, 
whose cases are all identical. The grammarians derive these surface forms from 
an underlying form, on which all three case endings are visible: /qa”ḍiyun/, 
/ qa”ḍiyin/, /qa”ḍiyan/; /ʾafʿayun/, /ʾafʿayin/, /ʾafʿayan/. According to them, 
the reason for these specific changes is that the speakers of Arabic dislike combi-
nations of the vowels 
i
and 
u
or of two 
a
’s with the glide 
y
, which they find too 
‘heavy’ to pronounce. The difference with the diptotic nouns is that weak nouns 
are actually declinable, even though their surface case endings are identical.
Apart from the case endings and the nunation, nouns may undergo morpholog
-
ical alterations, that is, changes in their form that are not caused by a governing 
word (
ʿāmil
). The most frequent alteration consists in the category of number: 
nouns may become dual or plural. The dual number of nouns is formed with 
suffixes, in the masculine 
-āni
for the nominative, 
-ayni
for the genitive/accusa-
tive; in the feminine 
-atāni
/
-atayni
. In the plural, we have to distinguish between 
a declension with suffixes (the so-called sound plural) and a declension by pattern 
modification (the so-called broken plural). The sound plural suffixes are 
-ūna
for the nominative, 
-īna
for the genitive/accusative; in the feminine nouns, the 
suffixes are 
-ātun
/
-ātin
. The sound plural is used almost exclusively for animate 
plurals and certain adjectives, as well as for the participles.
Because of the abovementioned principle (p. 110) of one-morph-one-meaning, 
the segmentation of the dual and plural endings constituted a major problem 
for Arabic grammarians. Take, for instance, the form