As the authors state in the introduction to the text, history is “the stories we tell about ourselves, or that others tell about us.” Those stories are fundamentally fashioned out of the sources that historians, themselves, decide are most valuable.
Historical narratives can be woven together in a multitude of ways, using many different kinds of sources, including material culture such as artifacts, oral histories and written materials. Understanding the “tripartite nature” (the division of sources into three genres: literary, diplomatic, social) of written historical materials can contribute immensely to the evaluation of sources by giving the historian a way to broadly categorize large amounts of historical sources that need be evaluated in the process of producing a particular historical narrative.
In that process of evaluation, the historian is asking one key question: “Out of all the available source materials, which among them will most effectively tell the story that I want to tell?” If, for example, one were writing a historical biography of a person, then “literary” documents such as journals and memoirs would be most valuable as primary sources. Other sources, such as “legal records” (diplomatic sources) and “government documents” (social documents) could be used as complimentary sources to lend credibility to what some might consider “ego-documents.” Conversely, if one were writing a narrative history of a company, such as a major nineteenth-century railroad, literary documents such as memoirs may not be as valuable as legal records and government documents.
In the end, being able to categorize sources into “Source Typologies” allows the historian to more effectively evaluate, organize and exploit a wide range of source materials in order to narrate, more precisely, the particular story they want to tell.