What was a common belief among historians in the early 20th century that makes their sources biased?

Historian of the late 20th century. (Nor did they realize they were living in the "antebellum" period.) The be lief that primary sources function as textual arguments lays the foundation for the third, and mostcommon, myth concerning primary sources. Myth 3. Historians use a 'sourcing heuristic" to evaluatebias and reliability.