If the mechanistic-reductionist cognitive approaches have been characterised by the metaphor of the “edifice”, of the solid Cartesian rock, all the forms of knowledge founded on complexity theory have been characterised by the metaphor of the “network”, of thinking in relationships, in a dynamic, fluid, open manner. In the field of mental illness, this means setting aside both the organicist paradigm and the pseudo-phenomenological, “sentimentalistic”, and therefore ideological, paradigm, in order to have an integrated view of biological objectiveness and humanistic psychotherapy. That is to say, an expression of diverse interrelated contributions from the various disciplines (psychiatry, psychology, biochemistry, anthropology, quantum physics, mathematics, philosophy). The observer thus becomes a builder of models, a manager of complexity, giving treatment the character of a truly empathic relationship. This is all the more so where distressing pathologies are involved, such as Major Depression (MD) and Bipolar Disorder (BD), caput mortuum of psychiatry, because the absence of cogent biological markers seriously compromises every form of therapy. Hence the identification of a biological platform (fatty acids of platelets) as a starting point for a correct classification of MD with respect to BD.