On the evening of October 5, 1955, Bion presented the paper “Differentiation between psychotic and non-psychotic personalities” to the British Society of Psychoanalysis. Two days later, on October 7, Winnicott commented on Bion's paper in a letter and in particular discussed its clinical material.

The author makes use of this exchange to examine how the transformations that took place in Bion's thought and Winnicott's contributions helped bring about a “quantum” revolution of the psychoanalytic paradigm. These may have facilitated the transition from an “epistemological” psychoanalysis (where what matters is what the analyst knows and the patient comes to know about himself) to an “ontological” psychoanalysis (where the presence of the analyst becocomes crucial - everything that the analyst is and the way in which he manages to “become” the patient's emotional experience).

And what we witness in ontological psychoanalysis is a significant clinical transformation, in which a theory of technique that focuses on interpretation can coexist with a theory of technique enriched with new tools - absence of memory and desire; negative capability (that is, the ability to be in doubt, anguish and chaos without developing too much persecution); being in emotional unison (at-one-ment); intuition; acts of Faith; capacity for reverie; language of Achievement; transformations into dream and play; becoming O (becoming the truth of the emotional experience of the patient and the session) - which make it possible to treat the most severely ill patients.