reverie is that state of mind which is open to the reception of any ‘objects’ from the loved object and is therefore capable of reception of the infant’s projective identifications whether they are felt by the infant to be good or bad. In short, reverie is a factor of the mother’s alpha-function.
Bion establishes reverie as the foundational maternal receptivity through which projective identifications are received and transformed by alpha-function, making it constitutive of the containing relationship.
, Learning from Experience, 1962thesis