The paper discusses the problem of personality development in its reflexive aspect and realization of its capacities within relationship with another person. Methodological bases of the study are psychology of personality, ontology and philosophy of life, existential philosophy, philosophy of language, phenomenology. Being a part of “general personology”, a new area of psychological science, the study uses the methods of hermeneutics, reflection, and theoretical modelling in order to extract and generalize the existing knowledge about the capacities of the I. Based on the ideas of M. Heidegger, J.-P. Sartre, and P. Ricoeur, the author develops a hermeneutic model of the multidimensional capacities of the I that are revealed within relationship with the Other. The model describes the genesis of these capacities and of awareness, of the I as a source of reflective mediation, and the forms these capacities take in the relationships of personality. It summarizes the types and dynamics of the capacities of the I in the dimensions of “between I and the Other”, “I-in-the-Other”, “the-Other-in-me”. The reflexive model of the capacities of the I can be used within practices of dialogical self-experience and self-development using retrospective analysis of oneself and one’s past expressions, as well as a practice of development of relationship with the Other. The vocal dialogue between the I and the Other is viewed within the life context of each of its participants, which reveals its personological nuances not represented in other human sciences.