One of the fundamental topics in the history of philosophy and theology is the issue of the personal identity of human beings during their lifetime in this world and hereafter. Philosophers have studied this issue from different perspectives and have raised conflicting opinions. This question has been raised to some extent by Avicenna and Mulla Sadra, and both philosophers have examined and answered the problem within their philosophical framework. Avicenna believes that mankind is one species whose immaterial soul is personalized and individualized by accidents, and with its survival, the identity and individuation of a human person are still preserved, even though his body has changed or completely destroyed. Mulla Sadra, according to his philosophical foundations, especially the substantial motion, believes that a person's identity is subject to existential change, and this continuous motion coincides with individual unity. Therefore, with the survival of this continuous and comprehensive being, the individual's identity is preserved in this world and hereafter. Accordingly, it can be said that the person in his/her life after death is the same as the worldly one, and in fact, an evolving person goes through sensory, imaginary, and in some cases intellectual stages. Although both opinions, based on their philosophical foundations, have significant and defensible points, they face challenges from the epistemological aspect. In other words, since both philosophers believe that the body –with its terrestrial features- is absent hereafter, how an observer can identify the other-worldly individuals with the worldly ones?