Modern standard Arabic nouns and adjectives fall into eight declensions. These categories of inflection are not usually treated separately as declensions in textbooks and grammars of Arabic, but I have found that this often leads to confusion for Arabic learners. I have therefore distinguished among all forms of nominal declension, including inflections for the suffix declensions of dual, sound feminine plural and sound masculine plural. Three-way inflection nominals (triptotes) are traditionally considered the base category because they exhibit three distinctive case-markings for nominative, genitive, and accusative. All other categories have fewer case distinctions: some two, some only one. Moreover, sometimes there is a distinction between definite and indefinite inflection, and sometimes not (for example, the declensions for the dual and for the sound masculine plural do not exhibit distinctions in definiteness).

Arabic nominal declensions:

Three-way inflection

1. (1) three-way inflection (‘triptote’)

Two-way inflection

1. (2) dual

2. (3) sound feminine plural

3. (4) sound masculine plural

4. (5) diptote

5. (6) defective

One-way inflection

1. (7) indeclinable (for case, but marking definiteness), and

2. (8) invariable