These definitions rely on external, “objective” criteria for determining who is in a family and who is not, which makes the definitions useful for groups like the US Census Bureau, lawmakers, and other researchers who need to define family for large-scale data collection.
However, a single person living alone or with nonrelated friends, or a couple who chooses not to or are not legally able to marry would not be considered a family. From this definition, a father and son, two cousins, or a brother and sister could be considered a family if they live together. One example of a structural definition of family is two or more people who live together and are related by birth, marriage, or adoption. Structural definitions of family focus on form, criteria for membership, and often hierarchy of family members.
The definitions people ascribe to families usually fall into at least one of the following categories: structural definitions, task-orientation definitions, and transactional definitions (Segrin & Flora, 2005). We can see from these examples that it’s not simple to define a family. But some people have a person not related by blood that they might refer to as aunt or uncle or even as a brother or sister. You may also name a person with whom you are in a committed relationship-a partner or spouse. Who do you consider part of your family? Many people would initially name people who they are related to by blood.