Paranoid-schizoid <-> Depressive oscillation (PS-D)

Bion uses the formula PS-D to refer to the paranoid-schizoid and depressive positions, and rather than seeing them as genetic positions, he sees them as states of mind that oscillate. This mental movement is necessary in the transformation process of psychic elements. The formula PS-D describes a movement from desaturation and incoherence to unity and coherence, and vice-versa. It is a model of transition between elements of thinking, as represented in Bion’s Grid. This transition based on PS-D oscillation is one of the pillars of Bion’s theory of thinking and became his model of creativity. While Klein linked creativity to the depressive position, for Bion creativity corresponded to the oscillation between PS and D.

Vermote, Rudi. Reading Bion (New Library of Psychoanalysis Teaching Series) (p. 18). Taylor and Francis. Kindle Edition.