Primary, Secondary, and Tertiary Sources

Primary, Secondary, and Tertiary Sources: A Quick Guide


A photograph can be a primary source

Antietam, Md. President Lincoln with Gen. George B. McClellan
and group of officers.
[October 3, 1862]
Gardner, Alexander, 1821-1882, photographer.
Source: Library of Congress, Prints & Photographs
Division, [reproduction number, e.g., LC-B8184-3287]
American Memory

What is a Primary Source?

Each academic discipline creates and uses primary and secondary sources differently; the definition of a primary source only makes sense in the context of a specific discipline or field of inquiry.
In the humanities and the arts, a primary document might be an original creative work.
It might be a part of the historical record written about, or in proximity to, an event.
In the sciences, it might be a publication of original research.

Here are two definitions that try to capture the elusive nature of primary documents:

A definition from Cornell: Primary sources are the main text or work that you are discussing (e.g. a sonnet by William Shakespeare; an opera by Mozart);
actual data or research results (e.g. a scientific article presenting original findings; statistics);
or historical documents (e.g. letters, pamphlets, political tracts, manifestoes).
["What is a Source?" Recognizing and Avoiding Plagarism. Cornell University. College of Arts and Sciences.]

A definition from Yale: "A primary source is firsthand testimony or direct evidence concerning a topic under investigation. The nature and value of a source cannot be determined without reference to the topic and questions it is meant to answer. The same document, or other piece of evidence, may be a primary source in one investigation and secondary in another. The search for primary sources does not, therefore, automatically include or exclude any category of records or documents."
[Yale University Library Primary Sources Research Colloquium in History]



Random examples of online collections of primary sources:


Secondary Sources

Secondary sources are books, periodicals, web sites, etc. that people write using the information from primary sources. They are not written by eyewitnesses to events, for instance, but use eyewitness accounts, photographs, diaries and other primary sources to reconstruct events or to support a writer's thesis about the events and their meaning. Many books you find in the Cornell Library Catalog are secondary sources.


Tertiary Sources

Tertiary sources are publications that summarize and digest the information in primary and secondary sources to provide background on a topic, idea, or event. Encyclopedias and biographical dictionaries are prime examples of tertiary sources.



Last edited 20 September 2013
Michael Engle
Research & Learning Services