In Arabic, "father" (أب) and "brother" (أخ) belong to a special grammatical group known as the "Five Nouns" (الأسماء الخمسة).
While most nouns show their grammatical case with short vowels, أب and أخ use long vowels when they act as the first part of an Idafa (possession structure) or attach to a pronoun suffix.
Nominative Case (مرفوع)
When acting as the subject of a sentence (or the subject of كان), these nouns take the long vowel و. Notice how أخ becomes أخو and أب becomes أبو.
| The baker's brother is an excellent manager. | أخو الخباز مدير ممتاز.akhû al-khabbâzi mudîrun mumtâzun |
| Your father was buying bread from the bakery. | كان أبوك يشتري الخبز من المخبز.kâna abûka yashtarî al-khubza mina al-makhbazi |
Accusative Case (منصوب)
When acting as the direct object of a verb, they take the long vowel ا. Here, أخ becomes أخا and أب becomes أبا.
| I saw the butcher's brother in front of the shop. | رأيت أخا الجزار أمام الدكان.ra'aytu akhâ al-jazzâri amâma ad-dukkâni |
| Boy, ask the grocer's father about the items. | يا ولد، اسأل أبا البقال عن الأغراض.yâ waladu, is'al abâ al-baqqâli 'ani al-aghrâd. |
Genitive Case (مجرور)
When following a preposition, or when acting as the possessor in a larger Idafa phrase, they take the long vowel ي. In this case, أخ becomes أخي and أب becomes أبي.
| I bought these items from the grocer's father. | اشتريت هذه الأغراض من أبي البقال.ishtaraytu hâdhihi l-aghrâda min abi l-baqqâl |
| The spice seller's brother's shop is very small. | دكان أخي العطار صغير جدا.dukkânu akhî al'attâri saghîrun jiddan |
Note: These special long-vowel endings apply only when the noun is possessed by another noun or by a pronoun. If you are just saying "a father" or "a brother" on its own, it declines with standard short vowels!
