ʿIllet is a metaphor for certain things that did not exist previously but came into being later. (Lumaʿ, 440)
ʿIllet is the indication (tanbīh) of the Real (al-Ḥaqq) through a cause or without a cause. (Iṣṭilāḥ, 534)
It is not obligatory with respect to the Essential Perfection (kamāl-i dhātī) and Essential Independence (ghinā-yi dhātī) (essential self-sufficiency).