A primary source is an original document/image, the results of an experiment, statistical data, first-hand account, or creative work. A secondary source is something written about or using primary sources. A teritary source is a collection of primary and secondary sources.
| Primary | Secondary | Tertiary |
|---|---|---|
| The text of The Gettysburg Address | An analysis of The Gettysburg Address | A U.S. history textbook |
| Census data for Detroit | A book about demographic changes in Detroit | A chronology of major events in Detroit |
| A McDonald's commerical | A documentary about McDonald's advertising | An encyclopedia of major marketing campaigns |
| The results of an experiment or clinical trial | An article citing different treatment options | An medical dictionary |
| An interview with a World War Two veteran | A documentary featuring interviews with veterans | An anthology of first hand accounts from World War Two |