The genealogy of knowledge consists of two separate bodies of knowledge: First, the dissenting opinions and theories that did not become the established and widely recognized and, second, the local beliefs and understandings (think of what nurses know about medicine that does not achieve power and general recognition). The genealogy is concerned with bringing these two knowledges, and their struggles to pass themselves on to others, out into the light of the day.
Genealogy does not claim to be more true than institutionalized knowledge, but merely to be the missing part of the puzzle. It works by isolating the central components of some current day political mechanism (such as maintainng the power structure which diagnoses mental illness) and then traces it back to its historical roots (Dreyfus and Rabinow, p.119). These historical roots are visible to us only through the two separate bodies of genealogical knowledge described above.
Foucault says, "Let us give the term 'genealogy' to the union of erudite knowledge and local memories which allows us to establish a historical knowledge of struggles and to make use of this knowledge tactically today. (Genealogy and social Criticism, p.42)"
The geneaalogical side of analysis tries to grasp the power of constituting a domain of objects. If a society were to institute the role of medicine man, for example, and give him special privileges, we would thereby "constitute the object of medicine man." Until we established and institutionalized this practice, nothing could be called a "medicine man." The genealogy explores what was not evident because of the institutionalization of knowledge by those in power.
(see Discourse on Language which is the appendix in the Archeology
of Knowledge.); Whereas archeology
studies the practices of language (in a strict sense), genealogy uncovers the creation of objects through institutional practices. (Dreyfus & Rabinow, p.104). Whereas the archeological historian claims to write from a neutral, disinterested perspective, the Nietzschean or Foucaultian genealogist admits the political and polemical interests motivating the writing of the history (Hoy, 1986, p.6-7)