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 provides the canonical definition of maternal reverie as the receptive, love-saturated component of the mother’s alpha-function, the mechanism by which the infant’s projective identifications are metabolized into thinkable experience.
, Learning from Experience, 1962thesis