The Lafayette College Library provides a synopsis of primary sources in several areas of study:
The definition of a primary source varies depending upon the academic discipline and the context in which it is used.
A history, whose author draws conclusions from other than primary sources or secondary sources actually based on primary sources, is by definition fiction and not history at all.
However, a primary source is not necessarily more of an authority or better than a secondary source. There can be bias and tacit unconscious views that twist historical information.
Original material may be... prejudiced, or at least not exactly what it claims to be.
Historians must occasionally contend with forged documents that purport to be primary sources. These forgeries have usually been constructed with a fraudulent purpose, such as promulgating legal rights, supporting false pedigrees, or promoting particular interpretations of historic events. The investigation of documents to determine their authenticity is called diplomatics.