Abstract

Infants apparently start to understand their experience via the linked concepts of numerical identity and spatio-temporally continuous objects during the forth month of life. As described by Piaget and Klein, this development requires them to synthesise their experience in a new ways: in particular they must start to acknowledge that the main target of their anger at frustration and the main target of their gratitude and love are the same person, who is unique and irreplaceable. This seems to have an immediate consequence in the onset of separation distress and stranger anxiety, and apparently has far-reaching psychological consequences later.