Rules Pertaining to the Dual Form
115. How many types of nouns are there?
116. How is the dual form formed?
117. How is a maqsūr noun put into the dual form?
118. How is a mamdūd noun put into the dual form?
119. How are nouns whose third root letter becomes erased put into the dual form?
115. There are three types of nouns: singular (a noun that indicates one item), dual (a noun that indicates two items), and plural (a noun that indicates more than two items).
116. The dual form is formed by adding an alif and nūn to the end of the singular noun when it is in the nominative case, for example: حَضَرَ الرَّجُلانِ or by adding a yā' and nūn to the end of the singular noun when it is in the accusative or genitive cases, for example: اِشتریا الکتابَینِ.
117. A triliteral maqsūr noun is put into the dual form returning its alif into its original state, for example عَصَا becomes عَصَوَان. If it is formed from a noun with more than three letters the alif is changed into a yā', for example: المُصطفیَ becomes المُصطَفَیان. If the yā' of a manqūs noun is erased it is returned when put into the dual form, for example: هادٍ becomes هادِیان.
118. If the mamdūd hamzah was added to put the noun in the feminine case it will be changed to a wāw, for example: حَمراء becomes حَمرَاوَان. If it was an original part of the word it will remain, for example: قَرَّاء becomes قَرَّاءان. If it was changed into an hamzah from a wāw or a yā' it is permissible to do one of the two previous actions, for example one can say دُعاءان or دُعاوان.
119. The third root letter in nouns whose third root letter is erased, for example أب returns when put into the dual form, for example: أبَوانِ. There are exceptions, for example: ید becomes یدان.