Primary vs. Secondary Sources: Differences and Examples by Field

Whether a source is primary or secondary is not a property of the document alone; it depends on what your paper is about. That idea, explained below with examples, clears up most of the confusion.

What is a primary source?

The Library of Congress calls primary sources the raw materials of history: original documents and objects created at the time under study (Library of Congress). Outside history, the same idea applies to firsthand evidence in any field. The University of Kansas writing center lists, among its examples, speeches, interviews, surveys or questionnaires, letters and diaries, scientific research reports, and literary works, films and art (KU Writing Center).

What is a secondary source?

Secondary sources are accounts that retell, analyze or interpret events, usually at a distance of time or place (Library of Congress). The KU writing center adds that their authors did not live through the events but researched other sources, just as you do in your own papers (KU Writing Center). Most scholarly books on a topic, and articles that analyze or review other work, are secondary sources.

What is the difference between primary and secondary sources?

Examples of primary and secondary sources by field

The same kind of document can play different roles in different fields. These examples show what usually counts in each.

A useful detail from the sciences: an article that reports a new study is a primary source, even though it is published in a journal and full of references. An article that reviews many studies is secondary.

Can a source be both primary and secondary?

Yes. The University of Massachusetts Boston library explains that whether something is a primary or secondary source often depends on the topic and its use: a biology textbook is secondary for a biology paper, but for a paper on the history of science education, textbooks can be primary sources (UMass Boston Healey Library).

Two more examples of the same switch:

• A 1995 newspaper analysis of the internet's future is secondary if your paper is about the internet, and primary if your paper is about how journalists imagined the internet in the 1990s.
• A famous scholar's 1970s book on a novel is secondary for a paper on the novel, and primary for a paper on how criticism of that novel changed over time.

So ask: is this document the evidence I'm studying, or a commentary on that evidence?

What are tertiary sources?

Tertiary sources index, abstract, organize, compile or digest other sources; some reference materials and textbooks count as tertiary when their main purpose is to list, summarize or repackage information, and they are usually not credited to a particular author (University of Minnesota Crookston Library). Typical examples are encyclopedias, dictionaries, handbooks, yearbooks and atlases, the reference materials the Library of Congress lists for background information (Library of Congress).

Tertiary sources are good for getting oriented and finding keywords and key works. They are rarely what an instructor wants cited as evidence in a college research paper.

How should you use each type in a research paper?

A strong paper usually combines both, each doing a different job:

1. Use primary sources as evidence. Quote or summarize them precisely and then explain what they show. Your analysis of primary sources is where your own contribution appears.
2. Use secondary sources to frame and test your argument. Show what scholars already say, where they agree, where they disagree, and where your reading fits.
3. Evaluate both. The KU writing center suggests asking what prompted a writer to produce a primary document and what their source of information and motivation were, and, for secondary sources, how well-informed and unbiased the author's judgments are (KU Writing Center).
4. Check what the assignment requires. Many history and literature assignments require a minimum number of primary sources; many science assignments expect original research articles rather than reviews.

Finding them: library catalogs, archives and digital collections for historical primary sources; journal databases for original studies and scholarly secondary works. See how to find scholarly sources for search tips, and how many sources for a research paper for how many of each to aim for.

What mistakes do students make with source types?

• Calling every old document primary. Age doesn't decide the type; the relationship to your topic does. A 1950s history textbook is still secondary for a paper on the event it describes.
• Treating review articles as original studies. A meta-analysis is valuable, but if the assignment asks for primary research, it doesn't count.
• Citing a quotation you only saw in a secondary source as if you read the original. Find the original if you can; if you can't, cite the source where you actually read it, following your citation style's rule for secondary citations.
• Using only secondary sources in a history or literature paper. Without primary evidence, the paper summarizes other people's arguments instead of making its own.

Where can you find primary sources?

Where you look depends on the field:

• Historical documents: your library's catalog (search your topic plus words such as letters, diaries, correspondence, speeches or sources), its special collections and archives, and the digital collections of national libraries and archives. The Library of Congress keeps a research guide to finding primary sources.
• Original research in the sciences and social sciences: journal databases. Filter for empirical studies, or check that the article has its own method and results sections rather than summarizing other work.
• Data: government statistical agencies and data repositories, and the datasets attached to published studies.
• Literature and art: the work itself, in a reliable edition your instructor accepts, plus published letters and interviews of the author or artist.

When you can't get the original, cite the version you actually used, such as a printed or digitized edition, rather than pretending you saw the original.

Quick test: primary or secondary?

The difference also shapes the kind of paper you write: a research paper leans on analyzing sources, while many essays lean on your own argument (more in research paper vs essay).