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Primary, Secondary, & Tertiary Sources

Complicating Factors

Now that we have some basic definitions, distinguishing between primary, secondary, and tertiary sources will be easy, right? Unfortunately, not always. Primary sources can be secondary sources. Secondary and tertiary sources can be primary sources.

In order to definitively decide whether a source is primary, secondary, or tertiary, you have to reflect on how it is used in research. In other words, the research application of a source will determine its source type. 

If the source in question is used as direct evidence or testimony of an event, experiment, or phenomenon, or if it was created by someone directly connected to the object of study, it is a primary source.

If the source in question is used to demonstrate that the researcher is aware other scholarship or to support their argument about primary sources, it is a secondary source. 

If the source in question is used primarily to learn general information on a topic, or as a reference tool to locate primary and/or secondary literature on a topic, it is a tertiary source. Tertiary sources are usually the easiest to identify.    

Examples by Discipline

In the humanities and social sciences, primary sources are the direct evidence or first-hand accounts of events without secondary analysis or interpretation. In contrast, secondary sources analyze or interpret historical events or creative works.

Primary sources Secondary sources Tertiary sources

Original works of art
Works of literature

Indexes, abstracts, bibliographies (used to locate a secondary source)
Journal articles


A primary source is an original document containing firsthand information about a topic. Different fields of study may use different types of primary sources. A secondary source contains commentary on or discussion about a primary source. The most important feature of secondary sources is that they offer an interpretation of information gathered from primary sources. A tertiary source presents summaries or condensed versions of materials, usually with references back to the primary and/or secondary sources. They can be a good place to look up facts or get a general overview of a subject, but they rarely contain original material.


Subject Primary Secondary Tertiary
Art A painting A critical review of the painting Encyclopedia entry on the artist
History  Civil War diary A book on a Civil War battle A list of battle sites
Literature A novel or a poem An essay about themes in the work A dictionary of literary terms
Political Science The Geneva Convention An article about prisoners of war A chronology of treatises

(Adapted from: VirginaTech Library under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.)

In the sciences, primary sources are documents that provide full description of the original research. For example, a primary source would be a journal article where scientists describe their research on the genetics of tobacco plants. A secondary source would be an article commenting or analyzing the scientists' research on tobacco.

Primary sources Secondary sources Tertiary sources

Conference proceedings
Lab notebooks
Technical reports
Theses and dissertations



These are where the results of original research are usually first published in the sciences. This makes them the best source of information on cutting edge topics. However the new ideas presented may not be fully refined or validated yet.

These tend to summarize the existing state of knowledge in a field at the time of publication. Secondary sources are good to find comparisons of different ideas and theories and to see how they may have changed over time.

These types of sources present condensed material, generally with references back to the primary and/or secondary literature. They can be a good place to look up data or to get an overview of a subject, but they rarely contain original material.


Subject Primary Secondary Tertiary

A conference paper on tobacco genetics

A review article on the current state of tobacco research An encyclopedia article on tobacco

A chemical patent

A book on chemical reactions

A table of related reactions


Einstein's diary

A biography on Einstein

A dictionary of relativity

(Source: VirginaTech Library under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.)