The Room
In the most carefully observed two-person relationship there is, the boundary between the two does not hold.
What was observed
Psychoanalysis began on the assumption that influence ran one way: from the patient's unconscious into speech, and from speech into the analyst's trained attention. The analyst was to be a surgeon and a mirror. Yet in 1915 Freud recorded that the unconscious of one person can react upon that of another without passing through consciousness, noted that the fact deserved investigation, and did not return to it.
The century that followed was a reluctant discovery of how much that remark contained. Paula Heimann (1950) found that the feelings arising in the analyst were specific to the patient and to the hour, and often ran ahead of understanding: countertransference was the patient's creation, set going in the analyst. Heinrich Racker showed that it is more precise than that. The analyst may feel not what the patient feels but what a figure in the patient's past felt toward the patient, and is playing that part before knowing there is a script. Harold Searles (1975) showed that the influence runs in both directions.
Madeleine and Willy Baranger (1961) proposed that the session is a single bipersonal field, producing a shared unconscious phantasy that belongs to neither participant. Its clearest evidence is the bastion: an impasse built from a piece of each person's inner life, interlocked, which neither built alone and neither can see. Thomas Ogden (1994), by a different route, named an analytic third, a subject created jointly by the pair. Antonino Ferro carried the line to its end: everything said in the room is the field describing itself.
What it shows
Each step moved the boundary of the relevant unit outward, from the patient, to the analyst's feelings, to the roles each was made to play, to the pair as one field, to the field with the two persons as its instruments. None of these writers set out to make a claim about the nature of persons. They kept running into it.
All of this was observed under the conditions most favourable to keeping two people separate: a fixed frame, a trained observer, one person speaking. What is unusual in the consulting room is the attention paid to participation, not the participation itself.