Why proximity to events shapes source ranking

Why do historians prioritize primary sources and rank evidence as primary, secondary, or tertiary?

Because source ranks describe distance from the event: firsthand accounts and contemporary documents preserve participants' observations and memories most directly.

Historians rank sources by how far they are removed from the event under study. An eyewitness account or an official document compiled at the time by participants counts as primary evidence in this framework. It preserves their observations and memories more directly than a later compilation, though every account remains partial. Primary, secondary, and tertiary describe a source's relationship to events, so the rank does not make any one version the whole truth.