Primary, Secondary, and Tertiary Sources

Purpose: After completing this section, you will be able to identify primary, secondary, and tertiary sources to meet research assignment requirements.

Why Are Sources Important?Primary SourcesSecondary SourcesTertiary SourcesBy DisciplineTelling the Difference

Why Are Sources Important?

Sources give your research validity.  Without fact-based research, your paper is 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:
    Some of your assignments require a certain number of primary sources—information from direct observation of an immediate event, or from empirical study. 
  • Secondary:
    Most sources used are likely to be secondary—analysis or interpretation of primary information. 
  • Tertiary:
    For an overview of, guide to, or compilation of sources, tertiary sources are useful. 
[2 min., 2012, Suffolk County Community College]

Right at the start, see how much you can discover about sources in this matchup.


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 the topic you are studying. 

Generally it is created at the time of the event, and it gives a witness’s or participant’s insight into 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.
  • Search for a relevant word. If your assignment requires that you 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 related to a survey, search for “survey”.

Primary sources can include peer-reviewed original research articles, news reports on current events, eyewitness accounts, diaries, manuscripts, speeches, historical and legal documents, statistical data, interviews, maps, oral histories, tools or other handmade artifacts, surveys, photographs, films, personal letters, creative writing (especially fiction), original music, poems, experiments, observations, and the like.

Secondary Sources

Clockwise: Books. Scholarly journals. Documentary film.

A secondary source is an interpretation, analysis, or restatement of 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 on the part of the author, and it is often an overview of, or aid to finding, primary or secondary sources. Normally, analysis and judgment are not significant parts of a tertiary source.  Instead, a tertiary source provides an introduction, pointer, or 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

Note that there is some overlap among the three divisions here, and that primary sources in one division may be used as secondary sources in another.


In fields related to 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

In fields related to 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

In 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.

Telling the Difference

Subtleties of Sources

Watch the below video to 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]

Try it Yourself!—Distinguishing among source types

Determining a source's level

Distinguishing between levels of sources can be tricky. A specific 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 cite information in the abstract or review of literature.

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 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—could be one primary source. In the sciences, a primary source would 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.
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 to have 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 evidence 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.