Primary sources were written at the time of the events they describe or created by authors with firsthand experience of those events. The content of primary sources is entirely original and does not typically include interpretation or evaluation of other sources.
Some examples include diaries, newspaper articles, theses, letters, autobiographies or memoirs, legislation, recordings or transcripts of speeches, census data, and photographs.
Secondary sources analyze and interpret primary sources, typically in order to make some sort of argument. Secondary sources could be published any time after the publication of the primary sources they refer to, from almost immediately after, to hundreds of years later.
Examples include articles or books that interpret original research or creative works, biographies, historical analyses.
Tertiary sources compile information from secondary and primary sources. They tend to be objective and factual.
Examples include encyclopedias, almanacs, bibliographies, textbooks, and other reference sources.
| Primary Source | Secondary Source | Tertiary Source |
|---|---|---|
| Census data for Bridgeport | A book about demographic changes in Bridgeport | A chronology of major events in Bridgeport |
| A McDonald's commercial | A documentary about McDonald's advertising | An encyclopedia of major marketing campaigns |
| An interview with a World War II veteran | A documentary featuring interviews with World War II veterans | A history textbook that mentions experiences of World War II veterans |
| A letter from George Washington | A book about George Washington | A Wikipedia article about U.S. presidents |