Knowledge of non-existent ideas and information on them in most ontological systems and, in particular, in Mulla Sadra’s philosophy of principality of existence is challenging in view of the principle of correspondence. Besides, affirmative information on non-existent ideas is controversial on the basis of principle of presupposition. This article is seeking to show how Mulla Sadra, based on the principality of existence and concomitance of existence and thingness, can inform us of non-existent ideas while preserving the principle of presupposition and based on the principle of correspondence. By relying on the creative power of the mind and conceptualizing it, Mulla Sadra has done theorizations on non-existent ideas in two ways: (1) difference of the two predicates, and (2) lā batiyya[1] propositions. The second way in Mulla Sadra’s expression faces some questions, including: (1) what are lā batiyya propositions? (2) How is confirmation of the subject in lā bitiyya propositions? And (3) What is the criterion for expansion of lā batiyya propositions up to the propositions related to necessary [being]? These questions are discussed here. This article uses an analytical and interpretive method to show although Mulla Sadra has paid no attention to the method of ‘thing-itself’ in resolving the problem of information on non-existent ideas, the richness of his system, due to the belief in principality of existence and the soul’s intuitive knowledge in rational intuition as well as the creativity of the mind in conceptualization, can preserve the principle of presupposition and correspondence and explain the information on non-existent ideas successfully. In Mulla Sadra’s view, our soul has a power to make a title for the subject of predicative lā batiyya propositions, and the judgment goes on the title that refers to the individual impossibility outside the mind. Then, what is in the mind is not really an individual who needs correspondence; rather, it is merely a general concept; and when we make judgments, it is a judgment on something that is a possible being, with no problem. Thus, the impossible beings have neither an actual instance in the mind, nor a nature whose judgment spreads to external individuals.