Avicenna: Essence, Existence, and the Soul

Abu Ali al-Husayn ibn Sina, known in Latin as Avicenna (c. 980-1037), a Persian polymath who served as physician and vizier to various rulers in Central Asia and Iran while composing an enormous philosophical and medical corpus (notably the encyclopedic Kitab al-Shifa, 'The Book of Healing,' and its medical companion, the Canon of Medicine), introduced into philosophy a distinction that would reshape medieval metaphysics: the real distinction between essence (mahiyya, or 'quiddity,' what a thing is) and existence (wujud, that a thing is). Avicenna observed that one can grasp the essence of a thing, for instance 'horseness' or 'triangularity,' completely, understanding fully what it would be for such a thing to exist, without thereby knowing whether any such thing actually exists; essence considered strictly 'in itself' is indifferent to, neither entailing nor excluding, either universal or particular existence. For every being in the created world, therefore, existence must be something added to essence by an external cause, since a thing's own essence alone cannot explain why it exists rather than not; only in one unique case, Avicenna argues, is existence not distinct from essence but identical with it.