What is i'rab (al-i'rāb)?
I'rab (إِعْرَاب) means to make a thing plain — to express it clearly. That is exactly what it does: the end of a word changes, and the change makes plain the job that word is doing in its sentence or phrase.
You already say all three every day. One name, three endings, one English translation.
| Where you say it | Transliteration | I'rab | |
|---|---|---|---|
| the shahādah | مُحَمَّدٌ رَسُولُ اللهِ | muhammadun | rafa |
| the tashahhud | أَنَّ مُحَمَّدًا رَسُولُ اللهِ | muhammadan | nasab |
| the ṣalawāt | صَلِّ عَلَى مُحَمَّدٍ | muhammadin | jarr |
The name never changes in English. In Arabic it changes three times, and each change is telling you what the word is doing in that sentence.
English does the same thing, but only on its pronouns — he came, I saw him, that is his. Say “his came to me” and it is wrong, though everyone knows who is meant. Arabic does this on every ism, not only on pronouns.
Two questions settle any i'rab, and they must be asked in this order. First: what role is this ism playing? The role dictates which of the three states it must be in. Second: what category of ism is it? The category dictates how that state is shown on the word. Role, i'rab, category, expression.
Every ism is in one of exactly three states of i'rab, and no more. Which one it must be in is decided by its role.
The roles are grouped by the state they produce: eight roles put an ism in rafa, twelve put it in nasab, and two put it in jarr.
Because the ending carries the role, Arabic can move its words about without losing the sense. نَصَرَ حَامِدٌ زَيْدًا and زَيْدًا نَصَرَ حَامِدٌ both say Hamid helped Zayd — the ـٌ and the ـًا decide who did what, not the order they stand in. English has to fix the order instead: change it, and “the mango ate Zayd” means something else entirely.
That freedom is not the same as order being meaningless. Arabic still has a normal order, and moving a word out of it is how the language gives emphasis or restriction — إِيَّاكَ نَعْبُدُ is “You alone we worship”, not simply “we worship You”. The order is free of the job of marking roles; it is not free of meaning.
But be careful how you read “the ending”. For most isms the state shows as a vowel on the last letter. For the dual, the two sound plurals and the five nouns it shows as a letter instead — مُسْلِمَانِ against مُسْلِمَيْنِ. And for a mabnī word or an ism ending in a fixed alif, nothing shows at all, and the role has to be read from the word's position and from the sense. Which of the three happens is settled by the category, and that is the next question after the role.
Like most Arabic grammar terms, إِعْرَاب (i'rab) was taken from everyday speech and then given one precise technical sense.
In everyday Arabic it means making something plain, expressing it clearly.
أَعْرَبَ عَنْ رَأْيِهِ (a'raba 'an ra'yihi) — “he made his opinion plain”
In Arabic grammar it means the change at the end of a word that makes the word's role plain. It is sometimes glossed as “to Arabise”, but that is a folk explanation rather than the meaning of the root.