The concept of the family is difficult to define. Part of the difficulty is that in everyday language, the term family is used to describe a number of relationships. These range from the biological, nuclear family of mother, father, and child and siblings, to the more extended family which includes several generations of blood relatives or relatives through marriage, to close and intimate friends, even to humankind, or the "family of man. "
The wide variation in everyday usage is less apparent in formal definitions, but even here there is a lack of consensus. Formal definitions do not always fit informal definitions. The U. S. Bureau of the Census, which collects information used by social scientists, defines family as "a group of two or more person related by blood, marriage, or adoption and residing together in a household. " A household is comprised of "all persons who occupy a housing unit, that is, a house, an apartment, or other group of rooms, or a single room that constitutes separate living quarters. " This definition considers the family in terms of only its structure and legal status, not the qualities of the relationship or its functions or activities. The Census Bureau thus would accept as a family two legally related people who hated each other and were just living together for their mutual economic advantage. Their definition also includes sexual and nonsexual relations; married women and men living together in sexual unions are families, but so are brothers and sisters living together in nonsexual unions.
Many social scientists often distinguish between the family of origin and the family of procreation (生殖, 生产). Most of us are simultaneously members of two families: the family of origin, into which we are born and of which we are always considered a member, even if we leave it, and the family of procreation, which we join as adults for the purpose of procreation and rearing children. Some social scientists also distinguish marriage from family and see the two as independent of one another. They argue that the family can exist regardless of whether the couple is married. They see marriage as a public ceremony which joins together two kinship groups and in so doing lays out some important rights over children, domestic authority, and sexual matters. Marriage is also the ritual through which children are made legitimate in the eyes of the parents and the society. Marriage therefore is a social ceremony, whereas family need not be.
An extended family ().
A. is composed of several nuclear families
B. does not include people with no blood relationships
C. includes close and intimate friends
D. is usually larger than a nuclear family