Arabic has three number forms: singular for one, dual for exactly two, and plural for three or more. This is different from English, which has no special form just for two.
We form the dual by adding «ان» or «ين» to the end of a singular noun. Example: «كتاب» (“book”) becomes «كتابان» or «كتابين» (“two books”), «بنت» (“girl”) becomes «بنتان» or «بنتين», and «قلم» (“pen”) becomes «قلمان» or «قلمين».
We use «ان» when the dual noun is the doer of the action, as in “The two boys came” (جاء الولدان), and «ين» in other cases, as in “I saw the two boys” (رأيتُ الولدين). Don't worry if this feels tricky at first — the important thing is grasping the idea of the dual itself.
