A soldier's letter home written during a battle tells you something different from a textbook written a century later. Historians weigh primary sources against secondary ones, always asking how they actually know what they claim.
History is an argument from evidence
History is not a list of facts but a disciplined argument built from surviving traces of the past. A primary source was produced at the time under study — a letter, a ledger, a photograph. A secondary source is a later interpretation, such as a scholarly book analyzing those letters.
Before trusting a source, ask: who made it, when, for whom, and why? Provenance and intent shape what a document can and cannot tell us.
A soldier's wartime diary is a primary source for morale; a 2010 monograph citing that diary is a secondary source interpreting it.
- Consider a tax roll compiled by a medieval town clerk in 1340.
- Ask whether it was produced during the period being studied.
- Classify it and name one bias it might carry.
What you should see: The tax roll is a primary source; its bias is that it records only taxable, propertied households — the poor may be invisible in it.