This article contributes to the platform of thought proposed by González Rey in the development of qualitative epistemology and the theory of subjectivity. We discuss three core aspects: firstly, the general epistemological problems of modern science, with its non-critical, non-theoretical scientific ideals, and low reflexivity; secondly, we propose Qualitative Epistemology as an alternative for the study of subjective processes and their complexity, explaining its fundamental principles and its scientific legitimacy. Finally, we present a set of interpretive constructions based on several cases from a Brazilian mental health service to illustrate the logic in the production of knowledge in Qualitative Epistemology. In this theoretical-empirical type of production, we show the heuristic value of this theoretical-epistemological framework to study phenomena that can only be understood and intervened using an approach that is equal as complex. This epistemological perspective could be useful for research around childhood and adulthood education, health, as well as other cultural processes, such as organisational and political dynamics. The human character of research is emphasised, or in other words, its intrinsically subjective dimension.