Since the reality of external existence never comes to the mind, and the only way to know it in acquired knowledge is through the concept of existence, here is a question as to how the mind can conceptualize this reality. Using a descriptive-analytical method, this study explores the dimensions, aspects, and roots of this question, and Allameh Tabatabai's answer, and analyzes his answer. According to the answer, the mind, in its first encounter with something like blackness, forms the proposition "This blackness is blackness," and from the independent reality of the judgment and attribution between the subject and the predicate—which is a mental phenomenon and a mental act and also a dual reality; in other words, it is both mental and indicative of the external —abstracts the concept in a perceptive form. It means that the mind represents the concept of "to be," and finds a path to the external reality. Subsequently, it looks at the relation and connection between the subject and predicate independently and forms an independent concept for it, which first appears as limited and added, i.e., the existence of the predicate for the subject, and then, without adding to the subject, it is conceived in an absolute form.