الإِسْمُ (The Noun / Name)
The noun is a phrase that names something and defines its meaning without indicating when it occurred in time, like ٌخَـالِـدٌ ,فَرَس and ٌعُـصْفُور. Information about the noun becomes clearer through its signs, like when it is prefixed with الْ like الـرَّجُـل or suffixed with tanwiin, like فَـرَسٍ or preceded by حرف النداء (the particle of address), like أَيُّـهَا النّاسُ or حرف الجر (preposition) like:
اِعْتِمدْ على مَنْ تُبُق بِهِ.
Nouns can either be مَعْرِيف (specific) or نَكَرَة (non-specific). The sign of a مَعْرِيف (specific noun) is الْ (the definite article) placed in the front of the noun like when you say: الـْمَسْجِـدُ and الْـبَيْتُ. The sign of a نَـكَرَة (non-specific noun) is the placement of تَـنْوِينٌ (tanwiin) on the last letter of the noun, like when you say شَجَرَةٌ and كَبِيرُ. The proper names can also be affixed with الْ and تَنْوِين like when you say: حَـسَنٌ and الـْـحَسَنُ. This الْ however does not cause the proper name to become definite because it in itself is specific/definite by its nature.
From the above discussion, we can see that الْ and تَـنْوِينٌ are two signs from among the signs which demonstrate that a word is a noun.
أَدَاة التَّعْرِيف (The Sign for Definiteness / Specification: الْ)
Any common or non-specific noun which has الْ prefixed to its front becomes a specific noun or definite noun.
The word تَّنْوِينُ (tanwiin) is a verbal noun; its closes meaning in English is ‘nuunation’ – that is to say that an Arabic noun has had the sound of the letter ن (nuun) placed on its last letter an therefore that letter has been ‘nuunated’ or ‘nuunized’ depending which way one chooses to anglicize this word.
The sign of تَـنْوِين (tanwiin) is the doubling of the short vowel signs and they become fat-ḥatayn, ḍammatayn, and kasratayn – like when you say ــً (an), ــٍ (in) and ــٌ (un) depending on the role the word is playing in the sentence.
تَّنْوِين (Tanwiin) as previously mentioned occurs as a sign of the noun, therefore تَّنْوِين (tanwiin) is one of the ways to determine whether or not a word in an Arabic sentence is a noun – like when you say: حَدَثَنِي رَجُلٌ عَنْ مُجَاهِدٍ خَاضَ مَعْرَكَةً دَامِـيَّةً (A man told me concerning Mujaahid that he rushed to a bloody battlefield.) In this sentence, every word which has تَّنْوِين (tanwiin) affixed to end is a noun. Its divisions are two: خَظًّا and وَقْعًا.
There are three kinds of تَّنْوِين (tanwiin):
1. تَّنْوِينُ التَّمْكِين is affixed to the fully declinable inflected nouns and because of this it is also called تَنْوِينُ الصرف (the tanwiin of the declinable noun), like when you say: رَجُـلٌ and كِـتَابٌ.
2. تَّنْوِينُ التَّنْكِير (Tanwiin of the Indefinite Noun) is affixed to the nouns fixed in their construction, like the noun that belongs with the verb and the closed proper name, i.e. (وَيْه) which is divided between the definite and indefinite. The noun that has tanwiin affixed to it is considered to be indefinite, while the noun which does not have tanwiin affixed to it is considered to be definite, like: صَـهْ وصَهٍ ومَهْ ومَهٍ وإِيهِ وإِيهٍ and like when you say مَرَرْتُ بسَبَوَيْهِ وسَـبَوَيْهٍ آخَر (I passed by Sabawayhi and Sabawayhin).
When you say: صَـهْ, what you are seeking from the person to whom you are speaking is that ceases the conversation he is involve in, and if you say to him: مَـهْ, what you desire from him is that he completes the conversation he is involved in, and when you say: إِيهِ, you want to add more to the conversation.
As for when you say to him: ومَـهٍ وإِيهٍ وصَـهٍ with tanwiin affixed to the end, you desire that he either ceases every conversation, completes every conversation or add to every conversation.
3. تَّنْوِينُ الْعِوَض (tanwiin of substitution) which is of three kinds:
a) تَّنْوِينُ الْـعِوَض (tanwiin of substitution) which is affixed to the end of the noun that is the substitute for the sentence when the noun that is being used as a substitute for the sentence replaces the sentence- like that which Allah the Most High has said: وَأَنْتُمْ حِينَئِذٍ تَنْظُرونَ () that is to say: حِينَ إِذْ بَلَغْتَ الرُّوحَ الْـحُلْقُوم تَنْظُرونَ (). And so you drop the sentence: بَلَغْتَ الرُّوحَ الْـحُلْقُوم and bring its substitute.
b) تَّنْوِينُ الْعِوَض (tanwiin of substitution)which is affixed to every noun that has been substituted for the noun that is construct with it in an idaafah – like when you say: كُـلٌّ قَـائِـمُ that is say: كُـلُّ إِنْسَانٍ قَـائِـمٌ. And so you drop إِنْـسَانٍ and replace it with the substitute noun that has tanwiin affixed to its end.
The words بَـعْدٌ and أَيُّ are similar to كُـلٌّ – like the statement of Ru’yah bin Mujaaj: دَايَنْتُ أَرْوَى وَالدُّيُون نَقَضَ فَمعلت بَعْضًا وَأَدْتُ بَعْضًا and أي أي امرئ.
c) تَّنْوِينُ الْـعِوَض (tanwiin of substitution) is affixed to the noun which is a substitute for the particle جَـوَارٍ and غَـوَاشٍ and similar to these are the broken nouns that are not fully declinable, and so تَّنْوِينُ الْـعِوَض (tanwiin of substitution) stands in the place of what has been dropped – like when you say: هؤلاء ضَـوارٍ and مَـرَرْتُ بِـضَوَارٍ, and so the letter ى has been replaced by تَّنْوِينُ الْـعِوَض (tanwiin of substitution) because the root word is ضَـوَارِي, however it is not تَّنْوِينُ التَّمْكِين () because it is not fully declinable.
Arabic Grammar – Preliminary Matters: Point 5 – الإِعْرَاب (Inflection) and الْبنَاء (The Fixed Construction)