Indefiniteness and Tanwin

Level: beginner. Modern Standard Arabic has no separate word for “a” or “an”. Instead, an indefinite noun carries tanwīn (nunation) — a doubled short-vowel mark at the end, pronounced with a final -n. So كِتَابٌ (kitābun) means “a book”, and the same noun loses the tanwīn when you make it definite with ال (al-).

The rule

A noun is indefinite when it refers to no particular one (“a book, some house”). In writing, Arabic shows this with tanwīn: a doubled vowel sign on the final letter that you hear as an added -n. There are three forms, one for each grammatical case (the noun’s job in the sentence):

• -un — the nominative (subject), written ـٌ (ḍammatān): كِتَابٌ (kitābun).
• -an — the accusative (object), written ـً (fatḥatān): كِتَابًا (kitāban).
• -in — the genitive (after a preposition or possessor), written ـٍ (kasratān): كِتَابٍ (kitābin).

Making the noun definite — by adding ال (al-), by a following possessor, or by a pronoun suffix — removes the tanwīn: كِتَابٌ (kitābun, “a book”) → الكِتَابُ (al-kitābu, “the book”).

The three indefinite endings

Notice the accusative usually gains a written alif — ـًا (an) — as in كِتَابًا (kitāban). This alif is silent; it just carries the -an.

Example sentences

Common mistakes

• ❌ الكِتَابٌ (al-kitābun) → ✅ الكِتَابُ (al-kitābu). With ال (al-) the noun is definite, so it drops the tanwīn.
• ❌ أُرِيدُ كِتَابٌ (urīdu kitābun) → ✅ أُرِيدُ كِتَابًا (urīdu kitāban). The object takes the accusative -an.
• ❌ مَدْرَسَةًا (madrasatan, with an extra alif) → ✅ مَدْرَسَةً (madrasatan). No alif after tā’ marbūṭa.
• ❌ فِي بَيْتٌ (fī baytun) → ✅ فِي بَيْتٍ (fī baytin). After a preposition the noun is genitive, -in.

A short conversation

— مَا هٰذَا؟ (mā hādhā?) — What is this? — هٰذَا كِتَابٌ. (hādhā kitābun.) — This is a book. — وَأَيْنَ القَلَمُ؟ (wa-ayna al-qalamu?) — And where is the pen? — عَلَى الطَّاوِلَةِ. (ʿalā aṭ-ṭāwilati.) — On the table.

Usage notes

• Case is heard in careful speech: in everyday spoken Arabic the final case vowels are often dropped, but in Modern Standard Arabic — news, reading aloud, exams — you pronounce the tanwīn.
• Three ways to become definite: the article ال (al-), a possessor in a construct phrase — بَيْتُ الرَّجُلِ (baytu ar-rajuli, “the man’s house”) — or a pronoun suffix such as كِتَابِي (kitābī, “my book”), each of which removes the tanwīn.
• Adjectives agree: an adjective describing an indefinite noun is also indefinite and takes tanwīn: بَيْتٌ كَبِيرٌ (baytun kabīrun, “a big house”).

Compared with…

• The definite article ال (al-) — the opposite of tanwīn: it marks the noun as “the”, and the two never appear together. See The Arabic Definite Article ال (al-).

Quick recap before the quiz.

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