Testing a source before trusting it: who made it, when, for whom, why, and how it survived.
Key thinkers: Marc Bloch, R.G. Collingwood, John Tosh
The longer story
Historical source criticism evaluates evidence from the past. External criticism: is this document authentic? Who created it, when, why? Internal criticism: what does it tell us, reliably, about its time? Every source has biases; the question is what biases and how they affect usefulness. Primary sources are closest to events; secondary sources interpret them. The historian triangulates, checks sources against each other, reads silences as well as presences. What doesn't the archive preserve?