Avicenna, being influenced by Farabi’s specific terms about the dual concepts of existence and quiddity, believed in external occurrence of existence upon quiddity in the contingents and the accidental synthesis of things from them. But Bahmanyar, the self-proclaimed commentator on Avicenna, expressly states in Al-Tahsil that the existence of a thing is the objectivity of its external quiddity and enumerates “existence”, like “substance” and “thing”, as intellectual fictions abstracted from existing quiddities. This paper scrutinizes this conflict, using the first-hand sources of peripatetic philosophers, then gives forth four distinctive interpretations of their beliefs regarding the existence and quiddity of things. Namely, thinkers such as Avicenna and Sohrevardi, recognized this conflict between Bahmanyar and his teacher, and strengthened the former’s views, whereas some orthodox peripatetic philosophers, specially commentators of Fusus-al-Hikmah ignored this difference and re-read and interpreted the theory of external occurrence of existence upon contingent quiddities. Mulla Sadra, taking into account this latter view, maintained two different opinions about Bahmanyar. But, sadly, most of Mulla Sadra’s commentators have read peripatetic philosopher’s sources based on Sadraic tradition, and therefore have remained unaware of their conflicts and the differences of their views.