How do biographers use letters, diaries, interviews, and photographs as evidence?

Biographers treat letters, diaries, interviews, and other personal documents as essential, though often complex, evidence in the craft of reconstructing a life. Because biography focuses on the particulars of an individual, these sources serve as the primary materials for understanding a subject's experiences and personality.1

However, biographers must rigorously test the authenticity and reliability of these materials. Challenges include:1

• Reliability: Older collections of papers and letters were often edited by predecessors who felt free to omit, transpose, or even falsify records to protect a subject's reputation.1
• Access and Availability: Biographers of contemporary figures may face an overwhelming "plethora" of materials, such as thousands of letters or transcripts, while others may find that key documents were intentionally destroyed to prevent a biography from being written.12
• Interpretation: When dealing with living subjects, biographers must weigh personal interviews against other, potentially contradictory sources. In the case of psychobiography, authors may interpret seemingly trivial details—such as a slip of the pen—as vital clues to a subject's unconscious mind, a practice that often diverges from traditional historical methods of weighing evidence.12

Ultimately, the biographer's chief responsibility is to apply consistent rules of evidence to evaluate these sources, regardless of whether the subject is long dead or a contemporary.1