A DYAD is the smallest social group - two people.  Consequently, the DYAD can be considered the basic building block of the scientific discipline of sociology and sociology's basic unit of measurement.  A theoretical DYAD is a social group of two people who interact reciprocally and form a social bond.  Social bonds are comprised of various aspects of positive, negative or neutral emotions.  DYADs and other larger social groups create, produce, modify and change cultures and subcultures.  Cultures are divided into material culture (physical objects and structures) and non-material culture (i.e., concepts, perceptions, symbols and mental images).  Partially excerpted from the lectures of Dr. Ivan Chapman, Sociology faculty, Oklahoma State University, Stillwater, Oklahoma, 1972.