time. When one fails to accomplish this second developmental task, this will result in a borderline pathology, meaning that objects or the self cannot be seen as both good and bad; something is good, or it is bad, but both affects cannot be in the same object together. Developmental stages Kernberg's model of self and object development rests on five stages that delineate the growth of the internalized object relations units, some of which already start taking place during the precipitating stage. The stages are not static, but fluent. Stage 1 (0 to 1 month): Normal autism This stage is marked by undifferentiated self-object representations. This stage is equated with Mahler, Pine and Bergman's conception of autism. Stage 2 (2 months to 6–8 months): Normal symbiosis In the beginning of this stage the child is unable to integrate opposing affective valences. Libidinally invested and aggressively invested representations are strictly separated into a 'good' self-object representation and a 'bad' self-object representation. Stage 3 (6–8 months to 18–36 months): Differentiation of self from object relations In this stage the 'good' self-object representation differentiates into a 'good' self and a 'good' object and shortly thereafter the 'bad' self-object representation differentiates into a 'bad' self and a 'bad' object. A failure of the child to differentiate between self and other results in a psychotic personality organization; one has failed to accomplish the first developmental task and is stuck in stage II. Although in this stage differentiation between self and object has taken place the good and bad self and object representations are strictly separated through the mechanism of splitting in order to protect the ideal, good relationship with the mother from contamination by bad self representations and bad representations of her. Stage 4 (36+ months through the oedipal period): The integration of self representations and object representations During this stage the 'good' (libidinally invested) and 'bad' (aggressively invested) self and object representations are integrated into a definite self-system and a total object representation. One is able to comprehend the possibility of the self or other containing both positive and negative characteristics. A failure of this results in a borderline personality organization; one has failed to accomplish the second developmental task and is stuck in stage III. Consequently, the good self and object must still be protected from the aggression by the splitting of good and bad. Stage 5: Consolidation of superego and ego integration