Difference between Rabbul Alamin and Rabbil Alamin

Question

I heard many people using the word Rabbul-Alameen. This article tells us to Reflect upon His saying, '(Rabbul-Alameen) the Lord of the Alameen (mankind, jinn and all that exists).' [Soorah al-Fatiha (1): 2] whereas v 1:2 is Alhamdu lillahi Rabbil Alamin.

So what is the difference between these two words? Should I address Allah as Rabbul-Alameen or Rabbil-Alamin in dua? Or are they synonyms of each other?

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_{I can sense that it is more of a question on Arabic language itself than on Islam. But ArabicSE has been abandoned, and this particular question is not suitable for LinguiticsSE. Hence, I asked it here seeking suggestion.}

Answer 1

short answer: both are the same words but in different diacritics(tashkeel) تشكيل

detailed answer: both words are the same "Rabb" (رب) but you add different diacritics(A َ, O ُ, E ِ )(tashkeel) تشكيل according to the word position and meaning inside the phrase as the grammar (Nahw) rules says

there are a lot of Nahw rules that governs you how to add the diacritics to the words - in fact this is the heart and sole of the Nahw rules -

to give you an example let us take the word (brother - أخ - Akh - a5) , and put it in different situations in different phrases to see how some Nahw rules apply to the same word and change it to the three different diacritics(A َ, O ُ, E ِ ) , and I will try to bring the most common rules and situations

1- (a - Fatha فتحه - Aَ )

the most common situation you put Fatha on the word, if it appears in the sentence as object (مفعول به - mafoul beh)

example: I thanked the brother - شكرت الأخَ - shakarto Al-Akh(a) when the word appears as an object you mostly are going to add (a) to it [1] see notes at the end

2- (o - dammah ضمة - oُ )

the most common situation you put damma on the word, if it appears in the sentence as subject (فاعل - fa`el)

example: the brother came - جاء الأخُ - jaa' Al-Akh(o) when the word appears as an subject you mostly are going to add (o) to it [1] see notes at the end

3- (e - kasrah كسرة- eِ )

the most common situation you put kasrah on the word, when the word come in the sentence after some of the letters of jarr(حروف الجر) (like the letter L "ل") as in Lellah - لله in verse [2:284]

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NOTE- 1 : the Nahw book says the situations I mentioned enforce you to change the word according to the type of word(Singular, plurals, ..etc) (some situations you will add ( diacritics - tashkeel - تشكيل ) like we did in example 1 for the Fatha , and some situations you add letters like( a ا , o و , e ي ), although you pronounce them the same most of the situations , but I had to note that.

for more information look at https://en.wikipedia.org/wiki/Arabic_diacritics

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regarding your example Alhamdu lillahi Rabbil Alamin , you add kasrah rabb(i)alalamin because it had the letter L ل before the word (li)llahi, which is another rule, and in duaa , I say (ya rabbi) meanning my god , and you can pronounce ya rabb(a)lalamin

Answer 2

Rabbul Alamin and Rabbil Alamin actually mean the same thing what makes them different is the pronunciation. So actually what makes them different? Simple, Arabic grammar(Nahw) is what makes them different. These are some of the reasons that makes them different.

Fa-il makes a thamma("u" or "oo") sound

A fa-il is someone who is responsible for something to happen e.g

Qala Rabbul Alamin

Said the Lord of the all those on earth(might have different meaning regarding the situation and who is translating it, most of the names of Allah (SW) are like this).

• In this case who said is the Lord, in short He is the cause of what is happening which is the act of saying.

Maf-ul bihi makes a fatiha("a") sound

Maf-ul bihi is someone or something acted upon or victim of an action e.g

Aswaita rabbal alamin You went against the Lord of those on earth.

• In this case "you" are the fa-il(the doer) and Rabb recieves the act of you going against Him.

Use of harf jarri (prepositions) makes a jarri or kasri("i" or "ee") sound

A-mantu bi Rabbil Alamin

I believe in the Lord of all those on earth.

This is so brief but hope it has sheds some light :)