Interactive chart showing how the evidential weight of five source types changes with the historical question asked of them
A propaganda poster is poor evidence until you change the question
Reliability is not a property of a source. It belongs to the pairing of a source with a question. A poster made to persuade is weak evidence of what happened in the street and strong evidence of what the state wanted believed. Change the question, then move across the five source types, and watch what each one can and cannot prove.
Source against question
Asking: what happened?
Change the question first. Then move across the source types and watch the bars reshuffle.
Question asked of the source
Poster · weak for what happened
Source typePoster
DiaryMemoSpeechPosterPhoto
Can prove
Cannot prove
Weight for this question (illustrative, 0–100)
15
Rank among the five sources
5th of 5
Which question to ask first
Know This
No source is reliable in itself: its value depends on the question you ask of it, and its limitations are whatever that question needs and the source cannot supply.