Primary, Secondary, and Tertiary Sources

Purpose: Identify primary, secondary, and tertiary sources to base your research on well-grounded information.

Why Are Sources Important?PrimarySecondaryTertiaryBy DisciplineTelling the Difference

Why Are Sources Important?

Sources give your research validity.  Without fact-based research, your paper is simply opinion. Good research is based on verified fact.

There are three levels of sources, based on how close they are to the event or topic being studied.

  • Primary:
    Information from direct observation of an immediate event, or from empirical study. Your assignment may require some primary sources.
  • Secondary:
    Analysis or interpretation of primary information. Most sources are secondary.
  • Tertiary:
    Overview of, guide to, or compilation of primary and secondary sources. 
[2 min., 2012, Suffolk County Community College]

Right away, see how much you can discover (or already know) about sources.


Primary Sources

Some primary sources. Clockwise from top left: Government document. Early snowshoes. Personal letters. Map. Report of original research. News report. Photo. Art.

A primary source is firsthand testimony, direct evidence, or an original creation about a topic. 

Generally, it is created near the time of the topic or event.  Research that is well-founded on primary sources can solidify the authority of a thesis.

In STEM fields, it can be difficult to verify what is a primary source. Here are a few ways:

  • Look at the structure. Typically, original research contains a set of sections such as Introduction, Review of Literature, Methodology, Results (charts), Conclusions, References. (Think IMRaD.)
  • Search for a relevant word. If your assignment requires you to include primary research in the form of an experiment, search for the word “experiment” within the body of the document. If you need to base your work on primary research obtained by a survey, search for “survey”.

Here are some typical primary sources.

experiment, eyewitness account, interview, observation, research article, survey, manuscript, photograph, film, handmade artifact, news report of current event, historical/legal document, map, oral history, original music, personal letter, statistical data, creative fiction, diary, poem, speech, tools.

Secondary Sources

Clockwise: Books. Scholarly journals. Documentary film.

A secondary source interprets, analyzes, or restates primary sources.

Often it attempts to describe or explain primary sources and give perspective to those sources.  It may compare, interpret, or document information on a topic, and in so doing may include photos, quotations, or other excerpts of primary sources. 

Secondary sources are often articles, reviews, biographies, essays, critiques, and books that interpret, analyze, or place in context a research work or works.  Most sources in a typical research paper are secondary sources.

Tertiary Sources

Online encyclopedia. Compiled references: atlas, dictionary, thesaurus, quotations. Timeline.

A tertiary source is compiled from primary and secondary sources.

Generally it *does not* include significant original work by the author, and it is often an overview of (or aid to finding) primary or secondary sources. Analysis and judgment are not significant parts of a tertiary source.  Instead, a tertiary source introduces, points to, or acts as a gateway to a subject.

Tertiary sources include almanacs, chronologies, summaries, timelines, dictionaries and encyclopedias, directories, guidebooks, indexes, manuals, and textbooks.

Types of Sources, by Discipline

There is some overlap among these three disciplines, and primary sources in one discipline may be considered secondary sources in another.


For fields in science, technology, engineering, and mathematics, including medicine —

Primary sources tend to be peer-reviewed original research articles, lab data, data sets, experiments, surveys, statistics, conference reports, algorithms, code libraries, and models. Sources for medicine- or healthcare-related fields may also make use of primary and secondary sources as listed in the social sciences.

Secondary sources can be books and articles about a primary research topic, reviews, editorial articles, biographies, newsletters, documentaries, and professional news sources.

Social Sciences

For fields in business, finance, political science, psychology, communications studies, education, sociology, and anthropology—

Primary sources include data sets, statistics, non-profit reports, recordings, speeches, government documents, legal documents, documents of record, peer-reviewed original research articles, test results, experiments, model, surveys, case studies, ethnograhies, recordings, oral histories, the evidence of experts (or in the case of journalism, the experts themselves), and case studies.

Secondary sources can be books and articles about primary sources or a social sciences topic, reviews, editorial articles, biographies, case studies, newsletters, documentaries, and professional news sources.

Humanities & History

For history and the humanities (arts, writing/literature, journalism, history, language, philosophy, religion)—

Primary sources include letters, autobiographies, manuscripts, speeches, historical and legal documents, interviews, maps, oral histories, diaries, memoirs, tools or other artifacts, recordings of events as they happen, photographs, [feature] films, personal letters, creative writing (especially fiction), original music, poems, plays, and original creative art.

Secondary sources can be biographies, reviews, books and articles about primary sources or a humanities topic, literary criticism, editorial articles, newsletters, documentaries, and professional news sources.

Learn More: Telling the Difference

Subtleties of Sources

Explore the finer distinctions among primary, secondary, and tertiary sources.  Complete with Australian accent and humor.

In-depth look at sources, with strategies to decide the type of source.
[6 min., 2020, Australian National Library]
Learn More: Determining a source's level

Distinguishing between levels of sources can be tricky. The same piece of information may be a primary source in one research project and a secondary source in another. Here are some tips:

All three levels of source can be in one document.  For example, a scholarly-journal article describing original research (primary source) likely contains an abstract (summarized info: tertiary) and a review of literature (comparison, interpretation, analysis: secondary). Generally, if your work requires a primary source, don’t use information in the review of literature or the abstract for that.

Consider the way you plan to use a source—as an artifact/evidence itself (primary)? or as a commentary on evidence (secondary)?  An opinion piece in a newspaper is normally considered a secondary source (commentary). But if your research topic *is* opinion pieces, this specific piece may be considered evidence (primary).

Think of the intellectual basis for the discipline you are working in. In arts/humanities, the original creative work you are studying—the painting, the novel, the piece of music—can be a primary source. In the sciences, a primary source can be an article detailing some original research, or a model of a scientific phenomenon. All these sources are “evidence” for their respective fields.

In summary, whether your source is primary, secondary, or tertiary depends on:

  • what part you use
  • how you use it, and
  • what discipline you are working in.
Learn More: Useful logic for sources

A useful logic test to decide level

Examples of primary and secondary sources are helpful, but they aren’t absolute. You need a strategy for deciding what type of source you’ve got.

A useful way to think about sources is: How close is the evidence to the event itself? Consider an example.

A photographer takes a significant photo of a protest as it is happening. That photo becomes a primary source: the evidence is very close to the event.

Ten years later, a student uses that photo in a research paper about the protest. The student includes the photo and then interprets it based on knowledge gained while creating the paper. That student’s interpretation now joins the body of knowledge as a secondary source: while the student considers the piece of evidence (the photo) closely, the student’s interpretation is separated from the event by time, other research, and the student’s exploration of other materials.

Distinguishing between primary and secondary sources is a profound element of research.  For further guidance, consult your instructor or a librarian.