Bion set about studying groups through observation and interpretation. He therefore combined the observational and experimental method. Interpretations are interventions which alter the behaviour of the group, so he observed the effect of these interpretations. As the group was his object of study he did not interpret the behaviour of individuals, though he was tempted to do so. So the members of the group would take their places and expected him to say something, explain how they were to proceed or do something to set the ball rolling. Instead of fulfilling their expectations he interpreted their expectations, of him and discovered that these interventions were most unwelcome. Through such a procedure he observed the way the group functioned and formulated certain principles about his observations.

He proposed that groups operate on two levels, the work level where concern is for completing the task) and the unconscious level where group members act as if they had made assumptions about the purpose of the group which may be different from its conscious level - dependency, flight, fight and pairing. Groups avoid the task at hand and emotional states hinder the task.

The Basic Assumption group process is about the group acting as if the members had made the basic and shared assumption that the group had met to do one of the following irrational things:

Depend on someone or something outside themselves (either within or outside the group). This is Basic Assumption Dependence or baD.

Fight or flee from something: Basic Assumption Fight/Flight or baF.

Pair or mate: Basic Assumption Pairing or baP.