A historical source encompasses "every kind of evidence that human beings have left of their past activities — the written word and spoken word, the shape of the landscape and the material artefact, the fine arts as well as photography and film.
"[3] In scholarship, a secondary source[4][5] is a document or recording that relates or discusses information originally presented elsewhere.
In a secondary source, the original information is selected, modified and arranged in a suitable format.
Secondary sources involve generalization, analysis, interpretation, or evaluation of the original information.
[7][8] Some tertiary sources can be used as an aid to find key (seminal) sources, key terms, general common knowledge[9] and established mainstream science on a topic.