Ṣadr al-Muta’allihīn (Mullā Ṣadrā) attributes external existence to the philosophical secondary intelligibles, asserting that these concepts, which exist in mind, also have corresponding referents in the external world. According to him, the mode of mental existence of philosophical concepts differs from that of essential concepts. Unlike essential concepts, philosophical concepts do not reflect the entirety of the essence and essential properties of their external referents and, therefore, do not possess mental existence in the same sense. These concepts are similar to abstract mental notions, such as "humanity," which signify their external reality and are abstracted directly from the essence of that reality. These accidental concepts signify an essence that is abstracted from the external essence. However, all the essences and essentials are not transferred to the mind and are not constituents of them. Only a mode of the modes has transferred to the mind. This study, through an analytical and critical method, examines and critiques Ṣadr al-Muta’allihīn’s perspective, presenting three objections: 1. Ṣadrā’s analysis of the mode of mental existence of philosophical concepts conflicts with his definition of conceptual knowledge (‘ilm ḥuṣūlī), which he restricts to essences. 2. When philosophical concepts signify their external existence in the form of a de re (wajh al-shay’) and provide a weak knowledge of these concepts, it constitutes an acknowledgment of conceptual knowledge (‘ilm ḥuṣūlī) of these concepts. 3. The arguments for mental existence are general and apply to philosophical concepts. To resolve these conflicts, it can be argued, first, that philosophical concepts indeed have mental existence. Second, a distinction must be made between exhaustive and non-exhaustive conceptual knowledge, for exhaustive conceptual knowledge applies to essences, while non-exhaustive conceptual knowledge pertains to philosophical concepts.