Primary sources are those items or documents that provide first-hand evidence of an organization, person, event, or location. These may include correspondence, diaries, convention proceedings, photographs, oral histories, paintings, songs, financial statements, memoirs, legal documents, autobiographies, posters, banners, motion pictures, lectures, advertisements or other materials created by someone based on direct experience, even if produced long after the original event.
Secondary sources are those that analyze, evaluate, and interpret primary sources. They often provide a commentary on the original documents but cannot provide direct, first-hand, evidence.
Whether a work is a primary or secondary source depends on the question under investigation. When a person writes an analytical essay or creates an artistic work focusing on something they have not directly witnessed, they produce a secondary source on that subject, but the same work may be used as a primary source when studying the author or creator.
Tertiary sources, such as encyclopedias and almanacs, collect, analyze, or summarize primary and secondary works.