Allameh Hassan-zada’s skill in resolving scientific disputes and reconciling the views of scientific schools in the way to achieve truth can assist us greatly in understanding and rightly interpreting the principality of existence and the meaning of conventionality of quiddity and its extension in the present time. The present article explores Allameh’s works in a descriptive-analytical way, adjust the important preliminaries in understanding the meaning of conventionality and predication of existence on quiddity, and regards two overall meaning for existence and non-existence of nature. First, predicating existence on quiddity is through medium of accidents and judging non-existence due to the rightness of its negation. Second, quiddity is non-existence in terms of relational existence, and is existent in terms of the existence of relation, i.e. the imperfect ‘to be’ (kāna nāqiṣa). Finally, we have explained the figurative existence of quiddity or its mystical judgment in Allameh Hassan-zada’s view.