Various theories of psychological development can be characterized according to whether they are primarily separation or attachment theories and whether they emphasize primarily the processes or the products of development. A full understanding of psychological development requires an integration of theories of attachment and separation and of what is attained in the course of psychological development (the products), as well as the mechanisms (or processes) by which these products are attained. Discussion of a revised model of Erikson's eight stages of psychosocial development illustrates the importance of formulating a dialectical developmental model that describes the interaction between attachment and separation and between product and process.