Primary vs. Secondary Sources

Researchers distinguish among primary, secondary and tertiary resources because each is useful in a different way.

A primary source is either a first-hand account of an event or generated by the event (such as data from an experiment). Primary sources are used as evidence.  Examples include:

  • bureaucratic records and documents
  • video and audio recordings
  • pamphlets, posters, newsletters, etc. (these “disposable” documents are called ephemera)
  • oral history transcripts and recordings
  • photographs and true-to-life illustrations
  • personal papers – diaries and letters
  • literature, plays, movies, music, art, etc. can be used as primary sources for studying the group or culture that produced them

A secondary source is a second-hand account; it is the researcher-author’s original thinking based on primary sources. Secondary sources interpret concepts. They are used to inform and substantiate a researcher’s interpretation of the evidence.  Examples include:

  • scholarly books (monographs) or articles
  • some nonscholarly books and articles
  • some documentaries

A tertiary source is third-hand, based on secondary sources. Tertiary sources are used to provide background information and are usually not cited in research because they are based on other scholars’ interpretations and are not original.  Examples include:

  • reference books
  • text books

Every time information is passed on, it is re-interpreted and possibly oversimplified or distorted. Use the original source of a fact or idea whenever possible.


  • For facts, use primary sources – data and first-hand reports.
  • For theory, analysis and interpretation, use secondary sources.
  • If one author talks about another’s idea, try to locate the original source of the idea.

Watch this tutorial from YouTube (created by UCSD Social Sciences and Humanities Library): What Is A Primary Source?

a brief course in information literacy