Final answer:
Emphasis in family development definitions is often on stage theories and family life cycle, which have been replaced by more fluid models like the family life course due to their limitations in accounting for diverse family forms.
Step-by-step explanation:
In definitions of family development, an emphasis is often put upon the concepts of stage theories and family life cycle. These concepts were traditionally used to describe the predictable stages that families were thought to evolve through over time. However, such theories have come under criticism for their linear and conventional assumptions and failure to represent the diversity of family forms. Instead, more flexible models like the family life course have been embraced, which view family events as parts of a fluid course rather than rigid, consecutive stages. This approach accounts for variations in family structures and recognizes non-traditional dynamics such as childbearing outside of marriage.
Moreover, the sociological understanding of what constitutes a family is not only defined by structure but also by how members relate to one another, fulfilling roles that support the emotional and economic well-being of the group. Symbolic interactionism and functionalism are sociological paradigms that help explain families as groups where individuals maintain emotional ties and perform essential societal roles.