Primary sources: original works of literature or art or a first-hand account of an event that has not been interpreted by anyone other than its creator. These sources were either created during the time period being studied, or were created at a later date by someone who participated in the events (ex: memoirs). They reflect the individual viewpoint of a participant or observer.
Examples of primary sources include diaries, letters, autobiographies, oral history interviews, speeches, organizational records, poetry, drama, sheet music, government documents, maps, artifacts, films, video, sound recordings, photographs, artwork, and natural specimens. Reports or articles describing original research and the results of that research are primary sources.
Secondary sources: commonly provide interpretation, commentary and analysis, and criticism of an historical event or phenomenon. These events are recounted by people who were not first-hand witnesses of the event (generally at least one step removed from the event).
Some examples of secondary sources are dictionaries, encyclopeadias, and reference materials.
| Title | Charles Darwin |
| Creator | Julia Margaret Cameron, European, British, English |
| Museum | San Francisco Museum of Modern Art, San Francisco, California, USA. 94.395 Accessions Committee fund: gift of Frances and John Bowes, Modern Art Council, Madeleine H. Russell, and Danielle and Brooks Walker, Jr. |
| Beginning Date | nobr 1868 /nobr |
| Ending Date | 1868 |
| Date | 1868 |
| Type | Photographs |
| Format (Medium) | albumen print |
| Format (Extent) | 13 3/4 in. x 11 3/4 in. |