This paper is a contribution to a debate that is currently taking place in the well-defended field of psychotherapy in Quebec, but also wherever interventions of this nature are practiced. Some are claiming “evidence-based practice” as defined by scientific criteria, in accordance with a particular definition of the word science. Others emphasize the relational dimension of the psychotherapeutic act, but without sacrificing its rigour. The reflections that follow will attempt to get to the root of this opposition, or at least to one possible source. As a part of this task, I will resort to thinkers preoccupied with the nature of science and the effect of its practice on the two major object categories: nature and human phenomena.