By combining philosophical knowledge with qualitative psychological research, the project will explore new interdisciplinary ways of addressing one aspect of the problem of personal identity, namely the distinctive uniqueness and irreplaceability of each individual person. The fact that we generally have no problem recognizing the same person across life changes suggests a kind of intuitive dualism, a grasp of an individual person-essence or soul, which remains the same despite modifications. Our project will explore ways of addressing a complementary issue in our understanding of personal identity, which we can express with a couple of questions: Is there any distinct perception of each person's uniqueness when all other characteristics, bodily and mental, are indistinguishable? That is, would we mind if the individual person we associate with were replaced, even though the physical features, memories, mannerisms, character, etc., remain the same? The purpose of the qualitative study is to explore the perception or awareness of this uniqueness in young adults, based on the assumption that we have a natural intuition about the irreplaceable nature of people.