One of the main proofs demonstrating the subsistence of the soul is the immateriality of the soul. However, solving the dilemma of the subsistence of all human souls depends on the analysis of the quality of the immateriality of the soul and demonstrating imaginal immateriality. Muḥaqqiq Ṭūsī has tried to prove the immateriality of the soul and has essentially propounded immateriality as an argument for demonstrating the subsistence of the soul. Although he has not referred to the demonstration of imaginal immateriality, some of the proofs he presents have the potential to be used in proving this kind of immateriality. On the other hand, he believes that the souls which have reached the level of rational immateriality also enjoy imaginal immateriality. Mullā Ṣadrā has also demonstrated the rational and imaginal types of immateriality in order to solve the problem of the subsistence of all souls and, basically, his attempts at demonstrating imaginal immateriality were at the service of demonstrating the subsistence of all souls. Some of Mullā Ṣadrā’s proofs are similar to those of Muḥaqqiq Ṭūsī. Mullā Ṣadrā believes that the application of some of these arguments to imaginal immateriality is perfect and, in addition to them, he also provides some independent reasons in order to demonstrate the rational and imaginal types of immateriality. Hence, through proving that the faculty of imagination is one of the levels of the soul and an immaterial thing by itself, he has managed to reason for the subsistence of the souls which have not moved forward from the level of imaginal immateriality. Here, the authors state that the arguments propounded by Muḥaqqiq Ṭūsī are capable of demonstrating imaginal immateriality and, accordingly, as Mullā Ṣadrā indicates, the subsistence of all human souls is possible in the light of demonstrating the imaginal immateriality of the soul. This has been clearly explained based on Sadrian principles; nevertheless, before Mullā Ṣadrā and in Muḥaqqiq Ṭūsī’s studies, imaginal immateriality can only be witnesses in those souls which have reached the level of rational immateriality. This argument cannot solve the problem of the subsistence of all human souls.