ABSTRACT
Most Shi'i philosophical treatises tackle the question of being by following a particular reading of Avicenna. Philosophers had noticed that in his Book of the Healing, Avicenna apparently drew a distinction between two dimensions, two aspects, in every existent: the essence of the existent and the concrete existence of the existent. All Shi'i philosophers since Nasir al-Din Tusi refer to God with the expression "the necessary in regard to being". God is always utmost existence, pure existence, without quiddity. His essence, therefore, is deprived of any definition of essence. The difference between God and the unnecessary things depends on the degree of intensity between these two orders: the order of the infinite and the order of the finite. Shi'i thinkers became familiar with the expression "the intelligible world" through their reading of Plotinus, though they attributed the notion to Aristotle, the "first master", and not to Plotinus.
