In previous posts, I explained the case marking system and the dual. In this post, I put explain them together in order to make their use together clearer. There are 2 endings that can be used with dual nouns and adjectives, i.e. (ان) and (ـَيْن). In the nominative case, i.e. when the noun is used as a subject or as predicate of nominal sentences, the nominative case applies and the ending (ان) is used, e.g.

درس الطالبان الجديدان في نفس الصف.

“Both new students studies at the same class.”

الكتابان الكبيران ثقيلان.

“The (2) big books are heavy.”

When the noun is used as an object, the case is accusative and the ending (ـَيْن) is used, e.g.

قرأت كتابين مفيدين.

“I read (2) useful books.”

قابلنا زميلتين قديمتين.

“We met (2) old colleagues.”

When the noun is used after a preposition or after the first word of an idafa construction, the case is genitive and the ending (ـَيْن) is used, e.g.

تكلمت مع صديقين جديدين.

“I spoke with (2) new friends.”

غرفة الطالبين واسعة.

“The room of the (2) students is spacious.”

It should be noted that the same applies to other dual forms that can be used with the nouns not only the adjectives, e.g. demonstratives and relative pronouns. Consider the use of the relative pronouns in the following sentences.

الطالبان الجديدان اللذان يدرسان في صفي لطيفان .

“The (2) new students who study at my class are nice.”

قابلت الطالبين الجديدين اللذين يدرسان في صفي.

“I met the (2) new students who study at my class.”

هاتان قصتان شيقتان.

“These are (2) interesting stories.”