A primary source is not the truth — it is a trace left by a person who wanted something. Historians read for the interest behind the words as carefully as for the words themselves.
Ask who paid for it
Chronicles, letters and inscriptions were commissioned. Knowing the patron usually explains the emphasis and the silences.
Date the copy, not just the text
Most ancient works survive through copies made centuries later. What changed in transmission is part of the evidence.
Look for the boring detail
Grain prices, ship manifests and tax rolls were written without an audience in mind, which makes them unusually reliable.
