Primary, Secondary, and Tertiary Sources


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

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 based on direct observation or 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]
An orientation to levels of sources.
[2 min., 2012, Suffolk County Community College]
Primary SourcesSecondary SourcesTertiary Sources

Primary Sources


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.

Examples of primary sources. Clockwise from top left: Government document []. Early snowshoes []. Letters []. Map [wikimedia commons]. Report of original research [PubMed]. News report [Eugene Register-Guard]. Photo [New York Times]. Art [wikimedia commons].

Secondary Sources


A secondary source offers 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.

Clockwise: Books [].  Scholarly journals []. Documentary film [wikimedia commons].

Tertiary Sources


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 or gateway into a subject.

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

Online encyclopedia []. Compiled references: atlas dictionary, thesaurus, collected quotations [JCU libguides]. Timeline [CDC].

Telling the Difference

Subtleties of sources

Video: Subtleties of sources

[6 min., 2020, Australian National Library]
In-depth look at sources, with strategies to decide the type of source.

Considers the finer distinctions among primary, secondary, and tertiary sources and how to distinguish which type you’ve got.  Complete with Australian accent and humor.

Determining a source's level

Determining how you are using sources

Differentiating between levels of sources can be tricky. 

The same information, may be a primary source in one research project and a secondary source in another. And different parts of a source may contain primary, secondary, or tertiary information.  The key is in the way you plan to use a source—as an artifact or evidence itself? (primary) or as a commentary on evidence? (secondary). 

You determine the nature and value of a source by considering the topic and questions you are using it to answer, as well as the nature of the information. 

Even so, your work on deciding is not trivial.  Think of an academic person giving a special lecture.  You decide the information is relevant to a paper you're working on and you want to use something the person said in your paper. 

  • If the speaker is describing something that happened to them, that they created, or that they witnessed directly . . .
    it's appropriate to use that material as a primary source, as evidence
  • If the speaker is comparing information from several sources, or systematically interpreting that information . . .
    that part of their speech is useful as a secondary source, one of several perspectives.

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).  The article as a whole is still mainly a primary source. 

Whether you consider a source as primary, secondary, or tertiary depends on:

  • what part you use
  • how you use it, and
  • in some cases, what discipline you are working in.

create the section below as a bordered example box

A key point about sources

Here is a useful way to think about sources: 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.

Twenty years later, a student uses that photo in a research paper about the protest. The student includes the photo and then gives an interpretation 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 has considered 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.

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

Try It Yourself!

Use these games to solidify your knowledge of sources and distinguish among the three types.

Characteristics of Primary, Secondary, and Tertiary Sources

Examples of sources


Case studies

1—Distinguishing among source types


2—Different uses for the same source

Sculpture of Beethoven

3—Avery’s project: Alaska Inuit


4—Carina’s project: stem cells

Stem cells