Primary vs Secondary Sources: Definitions and Examples by Field

A primary source is first-hand evidence or original research, such as a diary, a photograph, a set of interview transcripts or a journal article that reports a new experiment. A secondary source interprets or summarizes primary sources, such as a history book, a biography or a review article that pulls together many studies.

Where the line falls depends on your field and your research question. Below are library definitions, a table of examples from four fields, and a straight answer on whether a systematic review is primary or secondary.

TL;DR

• Primary sources were created at the time or report original research. Secondary sources work from them. Tertiary sources, like encyclopedias, condense both.

• In history, a journal article is usually secondary. In the sciences, an article reporting a new study is primary and a review article is secondary.

• Most library guides list systematic reviews and meta-analyses as secondary sources.

• Quoting something you only saw inside another work? Cite it with “as cited in” (APA) or “qtd. in” (MLA).

The difference in two sentences

The Library of Congress calls primary sources “the raw materials of history,” meaning “original documents and objects that were created at the time under study.” Secondary sources, in the same guide, are “accounts that retell, analyze, or interpret events, usually at a distance of time or place.”

Tertiary sources sit one step further out. The University of Kentucky Libraries describe a tertiary source as one that “presents summaries or condensed versions of materials.” Think encyclopedias, dictionaries and handbooks.

Scientists use the same words a little differently. The UC Berkeley Library says primary literature in the sciences “documents the results of original research” and is written by the people who did that research, while secondary literature “summarizes, compares, critiques, or interprets the primary literature.”

Primary vs secondary vs tertiary sources: key differences

Each row sets the three types side by side, with one example per field.

How the line moves by field

History and the humanities

Historians and literature scholars care about when a source was made, and by whom. Letters, diaries, speeches, photographs, court records, period newspapers, novels and films are primary. A historian’s journal article is usually secondary, because it interprets those materials.

Primary doesn’t have to mean written on the day. Pigafetta kept a journal at sea but wrote his full account back in Europe, and it counts as primary because he was there.

The sciences

In biology, medicine and engineering, the journal article itself is often the primary source. A paper reporting a new experiment, trial or field survey is primary literature, while review articles and meta-analyses are secondary.

Newspapers show how far the line moves. A 1918 report on a flu outbreak is primary for a historian, but a news story about a vaccine trial is secondary for a scientist, because the trial paper is the original.

The social sciences

Psychology, sociology, economics and education use both senses. Survey responses, interview recordings and census returns are primary, and so is an article reporting a new study built on them. A review summing up ten years of studies is secondary.

Your question can change the label

Ohio University Libraries put it plainly: whether something is primary “can depend on your particular research question.” Their example is textbooks. These are normally secondary, but if you are studying how late 19th-century history textbooks taught the Civil War, those textbooks become your primary sources.

Libraries don’t fully agree on textbooks, either. The University of British Columbia’s science guide lists an undergraduate textbook as tertiary. If your instructor defines the terms differently, follow your instructor.

Is a systematic review a primary or secondary source?

In most library guides, it’s secondary. A systematic review gathers and appraises the primary studies on one question and synthesizes their results, so its authors work from other people’s data. Drexel University Libraries list “review articles, systematic reviews, and meta-analyses” as examples of secondary sources, and the Rush University library puts systematic reviews and meta-analysis in its secondary column.

There is some nuance. The MUSC Library’s nursing guide notes that systematic reviews “can be both primary and secondary source” because their authors create new understanding by reviewing earlier research. A meta-analysis, for instance, produces a pooled estimate that none of the included studies reported. And in an umbrella review, which the University of Toronto Libraries describe, quoting Booth, as “a cluster of existing systematic reviews on a shared topic,” the systematic reviews become the raw material.

So for most coursework, call it secondary, and don’t count one when an assignment asks for primary research articles. For the method itself, see what a systematic review is.

Primary vs secondary research

These terms describe what you do, not what you read. A Leeds Beckett University guide sums it up: primary research data means “you collect the data yourself,” and secondary research data means “using information someone else has already collected.”

Primary research means surveys, interviews, focus groups, observation or experiments. Secondary research works with existing data, such as census figures, medical records or published studies.

The two pairs of terms don’t line up neatly. A team that runs a new analysis of census data is doing secondary research, but its paper reports new findings, so readers treat that paper as a primary source. Most theses use both kinds of research.

How to tell whether an article is primary, and where to find primary sources

Signs an article reports original research

The Salt Lake Community College library suggests four checks:

1. The authors did the work. Their introduction says what they are presenting, rather than only surveying other groups’ findings.

2. The abstract uses verbs like “measured,” “analyzed” and “investigated.”

3. A methods section explains the study in enough detail for someone else to repeat it.

4. There are results: new data in tables, graphs or statistics.

Reviews give themselves away too. Their methods describe database searches and inclusion criteria, not participants or lab work, and the title or abstract often says “review.” Olympic College Libraries make the same point from the other side: if the authors did any clinical work themselves, the article is not a systematic review or meta-analysis.

Where to find primary sources

For history and the humanities, start with archives. The Library of Congress digital collections include photographs, maps, sound recordings and personal papers, and the National Archives of the Philippines keeps a Spanish Documents Section that has been declared a National Cultural Treasure.

For the sciences and social sciences, you want research articles. PubMed’s article type filters can narrow results to clinical trials, or to reviews when that is what you need. Our AI academic paper search lets you ask a research question, set filters such as a date range first, and save the papers you want to a library. Then open each one and run the four checks above. For databases and search strings, see our guide to finding scholarly articles.

Citing a source you found inside another source

APA Style uses “secondary source” narrowly here, meaning the work where you found the quote. It says to use these sparingly and to find, read and cite the original where you can. If you can’t, list the source you actually read in your references. In the text, name the original, then add “as cited in” and the source you read, with the original’s year if known: (Rabbitt, 1982, as cited in Lyon et al., 2014). Only Lyon et al. goes in the reference list. With no known year, leave it out: Allport’s diary (as cited in Nicholson, 2003). The rule is in Section 8.6 of the Publication Manual.

MLA uses “qtd. in.” The MLA Style Center gives this example: According to Alexander Pope, “A little learning is a dang’rous thing” (qtd. in Damrosch 239). The works-cited entry is for Damrosch’s book, the one the writer actually read. Pope’s name could also go inside the parentheses, as in (Alexander Pope qtd. in Damrosch 239), or in a note. MLA agrees with APA that it is “always best to consult the original” when you can.

Mistakes that mislabel a source

• Calling every journal article primary. A review article in a science journal is secondary.

• Assuming old means primary. A history written in 1900 is still secondary, unless your topic is how people wrote history in 1900.

• Listing a systematic review as primary research when the assignment asks for original studies.

• Mixing up primary research, which you do, with primary sources, which you read.

• Resting a thesis argument on tertiary sources. Use encyclopedias to get oriented, then cite what they cite.

Can an AI search tool sort primary from secondary for you?

It can speed up the search, but the label is your call. Open each AnswerThis result and check its abstract and methods before calling it primary. A paper search covers published research, so for letters, photographs or colonial records, go to an archive.

FAQs

Is an interview a primary source?

Yes. An interview recording or transcript is first-hand evidence, whether you ran the interview yourself or found it in an oral history archive.

Is a textbook a primary source?

Usually not. Library guides list textbooks as secondary or tertiary. A textbook becomes primary only when the textbook itself is what you are studying.

Is a meta-analysis a primary source?

Most library guides list meta-analyses as secondary, alongside systematic reviews, because they pool results from primary studies rather than collecting new data.

Is a thesis or dissertation a primary source?

If it reports the author’s own original research, yes, in the same way a research article does. Its literature review chapter, though, works like a secondary source.

Is Wikipedia a tertiary source?

Yes. It summarizes other published sources, which makes it handy for background and key terms. Follow its references to the primary and secondary sources, and cite those instead.

Ready to look for original research on your topic? Start with our AI academic paper search, then check each paper’s methods before you call it primary.