The purpose of this article is to demonstrate that when Winnicott chose human nature as his object of study and psychotherapeutic care, he ended by reformulating the place of epistemological relevance of psychoanalysis as a science, leading it from the field of sciences of nature, as Freud intended, to the field of a scientific psychology of phenomenological and existentialist base. Such changes become clear both through the place given to the notion of being, that of true and false self, that of man as creator of world (with transitional phenomena), among other proposals that are similar to notions resulting from modern existentialism, and through the redescription of the psychoanalytic theory of emotional development, as a theory of health, designed and described in terms of the individual’s dependence on the environment and through different integrations related to oneself.