Al-muqaddimah Al-ajurrumiyyah [on the Science of Arabic Grammar]

The Chapter on I‘RĀB[17]

I‘rāb [^18] is a change affecting the endings of words[^19] due to the difference in the ‘Awāmil[^20] that enter and operate on them, (whether the change is) Lafđan (real and explicit, such that it can be verbally expressed) or Taqdīran[^21] (hypothetical and implicit, such that it cannot be verbally expressed but is instead assumed in the mind).

Its types are four: Raf‘, Naṣb, Khafḍ and Jazm.

Of this, Raf‘, Naṣb and Khafḍ apply to the Asmā’ (nouns) while Jazm does not feature in them at all.

Of this, Raf‘, Naṣb and Jazm apply to the Af‘āl (verbs) while Khafḍ does not feature in them at all.