Family is the basic unit of society and provides emotional, cognitive, physical, social, and spiritual development for its members. It consists of individuals who work together to overcome life's challenges through permanent love, harmony, and by aiding one another's upbringing. Families undergo stages in their life cycle from the beginning with a bride and groom, to expanding with daily family routines and stresses, to contracting in the empty nest period. Families are also classified by their authority structure as patriarchal, matriarchal, or egalitarian, and by their organization as nuclear, extended, or household.