Demonstrating the principality or fundamental reality of existence makes it clear that quiddity is but a mental construction and devoid of any actuality by essence. Three assumptions, however, can be made on its mode of being: 1. Its being identical to existence as in the case of Divine Attributes in relation to His Essence; 2. Its being as negation and limit of existence like line in comparison with surface or a point which is the end of a line; 3. Its being totally mental like an optical phenomenon of mirage. The late Allama Tabatabae and some of his disciples explicitly identify quiddity as a mirage while no sound arguments are made for the claim. Furthermore, there are many evidences in favor of identity of existence and quiddity. To name a few, one can make reference to mental being as corresponding to extra-mental existence of "natural universal", perception of the nature of sorrow and joy through knowledge by presence, and some arguments for the principality of existence in which the reality of quiddity are taken for granted.
)