The Noun الاسم alism in Arabic, any noun that is derived from the verb, can be either Indefinite نَكِرَة nakirah or Definite مَعْرِفَة ma‘rifah. The Indefinite النَّكِرَة an-nakirah is almost always changeable to Definite following to two morphological rules. Not every Definite, however, is changeable to Indefinite. That is, there are certain nouns that exist only in the Definite form, i.e. not back-formed to Indefinite.

The Indefinite النَّكِرَة:

The Indefinite Noun in Arabic is the noun that refers to non-specific entity. It is the default form of nouns that its definite counter form is derived from. In MSA, Indefiniteness is marked, i.e. clearly specified, by using nunnation تَنْوِيْن tanween. tanween in Arabic essentially means that the noun is indefinite. One of three forms of tanween is added to the end of the noun, that is tanween al-fatH ً , tanween al-kasr ٍ , or tanween aDHamm ٌ. The type of tanween that is added to the noun depends on the grammatical position of the noun, i.e. subject, object of a verb, or object of a preposition. In colloquial Arabic, Arabic speakers opt for تَسْكِيْن taskeen, i.e. avoiding final diacritical marks altogether, as in this list:

Dialects	MSA
كِتَاب	كِتَابًا ، كَتَابٍ ، كِتَابٌ  ‘a book’
سَيَّارَة	سَيَّارَةً ، سَيَّارَةٍ ، سَيَّارَةٌ ‘a car’
رَجُل	رَجُلاً ، رَجُلٍ ، رَجُلٌ ‘a man’
مَدِيْنَة	مَدِيْنَةً ، مَدِيْنَةٍ ، مَدِيْنَةٌ ‘a city’

The Definite المَعْرِفَة:

The Definite Noun in Arabic is the noun that refers to a specific entity. There are three types of Definite Nouns: 1) definite nouns that exist in Arabic Language to refer to something specific only. These include pronouns, such as أَنَا, هُوَ, هِيَ and alike; demonstrative pronouns, such as هَذَا, هَذِهِ and alike; and relative pronouns, such as الَّذِي, الَّتِي and alike. 2) the proper nouns which refer to nouns that people use to refer to a specific person or place, such as أَحْمَد, فَاطِمَة, جُورْج, دُبَيْ, سُورِيَا and so forth. 3) definite nouns that are derived from the basic form, i.e. changing the Indefinite Noun into a Definite Noun.

There are two ways to change an indefinite noun in Arabic to a definite: 1) by adding the Arabic definite article الـ to the beginning of the indefinite noun and 2) by adding the indefinite noun to a definite noun, i.e. forming إِضَافَة iDHafah structure.

Definiteness using الـ:

Making an indefinite noun in Arabic definite using this rule is straightforward. You simply add the الـ to the beginning of the indefinite noun. In MSA, the tanween is to disappear and is to be replaced by the corresponding single diacritical mark, i.e. fatHah َ , kasrah ِ, or DHammah ُ. In Dialects, the only apparent change is the addition of الـ. Here is how the above list would look like after adding الـ.

Dialects	MSA
الكِتَاب	الكِتَابَ ، الكِتَابِ ، الكِـتَابُ  ‘the book’
السَّيَّارَة	السَّيَّارَةَ ، السَّيَّارَةِ ، السَّيَّارَةُ ‘the car’
الرَّجُل	الرَّجُلَ ، الرَّجُلِ ، الرَّجُلُ ‘the man’
المَدِيْنَة	المَدِيْنَةً ، المَدِيْنَةُ ، المَدِيْنَةِ ‘the city’

Another thing you should mind while changing the indefinite into definite in this way is the pronunciation of الـ. If the letter following الـ belongs to the Sun Letters category, it must be assimilated. If it belongs to the Moon Letters category, it mustn’t be assimilated. Hence, the definite article الـ is what distinguishes the Definite المَعْرِفَة from the Indefinite النَّكِرَة.

Definiteness by iDHafah إِضَافَة:

iDHafah in Arabic means addition. In the case of definiteness, it means adding the indefinite noun to another noun that is already definite. That is, we add the indefinite noun to any of the abovementioned types of definite nouns. In all cases, the indefinite nouns must precede the definite. The indefinite is called مُضَاف muDHaf ‘the added’, while the definite is called مُضَاف إِلَيْه muDHaf iliih ‘the added to’ Let’s look at them one by one.

• Adding the indefinite noun to a pronoun:

In this case, you must note that the separate pronoun changes to its corresponding object (attached) pronoun as it is attached to the indefinite noun, hence for أَنْتَ , use كَ; for أَنْتِ , use كِ; for أَنْتَم , use كُم; for أَنْتُمَا , use كُمَا; and so forth.

إِضَافَة : نَكِرَة = مَعْرِفَة	مُضَاف إِلَيْه – مَعْرِفَة	مُضَاف – نَكِرَة
كِتَابِي ‘my book’	أَنَا – ي	كِتَاب
سَيَّارَتُها ‘her car’	هِيَ – ها	سَيَّارَة
مَدِيْنَتُنَا ‘our city’	نَحْنُ – نَا	مَدِيْنَة

• Adding it to a proper noun:

إِضَافَة : نَكِرَة = مَعْرِفَة	مُضَاف إِلَيْه – مَعْرِفَة	مُضَاف – نَكِرَة
كِتَابُ خَالد ‘Khalid’s book’	خَالِد	كِتَاب
سَيَّارَةُ فَاطِمَة ‘Fatima’s car’	فَاطِمَة	سَيَّارَة
مَدِيْنَة صَنْعَاء ‘Sana’a city’	صَنْعَاء	مَدِيْنَة

• Adding it to a demonstrative pronoun:

إِضَافَة : نَكِرَة = مَعْرِفَة	مُضَاف إِلَيْه – مَعْرِفَة	مُضَاف – نَكِرَة
كِتَابُ هَذَا الوَلد ‘this boy’s book’	هَذا	كِتَاب
سَيَّارَةُ هَذِهِ المَرْأَة ‘this women’s car’	هَذِهِ	سَيَّارَة
مَدِيْنَةُ هَؤْلاءَ الرِّجَال ‘these men’s city’	هَؤْلاءَ	مَدِيْنَة

• Adding it to a relative pronoun

إِضَافَة – نَكِرَة = مَعْرِفَة	مُضَاف إِلَيْه – مَعْرِفَة	مُضَاف – نَكِرَة
كِتَابُ الَّذِي فِي الصَّف ‘the book of the one who’s in class’	الَّذِي	كِتَاب
سَيَّارَةُ الَّتِي فِي المَطْعَم ‘the book of the one who’s in the restaurant’	الَّتِي	سَيَّارَة
مَدِيْنَةُ الَّذِيْن يُقَاتُلُون ‘the city of those who are fighting’	الَّذِيْن	مَدِيْنَة

• Adding it to a definite noun with الـ

إِضَافَة – نَكِرَة = مَعْرِفَة	مُضَاف إِلَيْه – مَعْرِفَة	مُضَاف – نَكِرَة
كِتَابُ الطَّالِب ‘the student’s book’	الطَّالِب	كِتَاب
سَيَّارَةُ المَرْأَة ‘the woman’s car’	المَرْأة	سَيَّارَة
مَدِيْنَةُ العُلَمَاء ‘the scholars’ city’	العُلَمَاء	مَدِيْنَة

• Adding it to yet another iDHafah:

إِضَافَة – نَكِرَة = مَعْرِفَة	مُضَاف إِلَيْه – مَعْرِفَة	مُضَاف – نَكِرَة
كِتَابُ مُدَرِّسِ الرِّيَاضِيَّات ‘math teacher’s book’	مُدَرِّس الرِّيَاضِيَّات	كِتَاب
سَيَّارَةُ صَدِيْقَتِي ‘my friend’s car’	صَدِيْقَتِي	سَيَّارَة
مَدِيْنَةُ طُلَّابِ الجَامَعَة ‘university students’ city’	طُلَّاب الجَامِعَة	مَدِيْنَة