The dual (المثنّى)

A separate form for exactly two

Arabic does not use the plural for two of something. It has its own ending, which any noun can take:

The ending replaces the tanween. As in the possessive, a final ة becomes ت: سَيَّارَة → سَيَّارَتَانِ.

• عِنْدِي كِتَابَانِ. — I have two books.
• رَأَيْتُ طَالِبَيْنِ فِي الْمَكْتَبَةِ. — I saw two students in the library.
• ذَهَبْتُ مَعَ صَدِيقَيْنِ. — I went with two friends.

The adjective is dual too

• طَالِبَانِ جَدِيدَانِ — two new students
• الطَّالِبَانِ الْجَدِيدَانِ — the two new students
• سَيَّارَتَانِ صَغِيرَتَانِ — two small cars

The nun disappears in an iḍāfa

When a dual noun is the first part of a possessive construct, it loses its ن:

• كِتَابَا الطَّالِبِ — the student's two books
• وَالِدَا أَحْمَدَ — Ahmad's parents
• فِي يَدَيِ الْوَلَدِ — in the boy's two hands

The same happens before a pronoun suffix: كِتَابَاهُ — his two books; يَدَيْهِ — his two hands.

Dual pronouns and verbs

• هُمَا يَدْرُسَانِ فِي الْجَامِعَةِ. — The two of them study at the university.
• هَلْ أَنْتُمَا جَاهِزَانِ؟ — Are you two ready?

The ن of يَكْتُبَانِ drops after أَنْ, لَنْ and لَمْ: لَنْ يَكْتُبَا.

Watch out as an English speaker

• English has no dual, so the plural feels natural for two. ✗ طَالِبُونَ اثْنَانِ / ✓ طَالِبَانِ.
• Do not leave ة before the ending. ✗ سَيَّارَةَانِ / ✓ سَيَّارَتَانِ.
• The ending changes with the case. ✗ رَأَيْتُ طَالِبَانِ. / ✓ رَأَيْتُ طَالِبَيْنِ.
• Drop the nun in a possessive phrase. ✗ كِتَابَانِ الطَّالِبِ / ✓ كِتَابَا الطَّالِبِ.

Example dialogue

كَمْ كِتَابًا عِنْدَكَ؟ — How many books do you have?
عِنْدِي كِتَابَانِ فَقَطْ. — I have only two books.
وَمَنْ هُمَا؟ — And who are those two?
هُمَا طَالِبَانِ جَدِيدَانِ فِي الصَّفِّ. — They are two new students in the class.
هَلْ يَدْرُسَانِ الْعَرَبِيَّةَ؟ — Do they study Arabic?
نَعَمْ، وَوَالِدَاهُمَا مُعَلِّمَانِ. — Yes, and their parents are teachers.