A primary source provides direct or firsthand evidence about an event, object, person, or work of art. Primary sources include historical and legal documents, eyewitness accounts, results of experiments, statistical data, pieces of creative writing, audio and video recordings, speeches, and art objects.

A secondary source is a source that provides an analysis of documents or articles at a later date or by people who were not directly involved in the original work. Examples include textbooks, review articles, and encyclopedias.