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Key takeaways
A primary source gives you direct access to the thing you are studying. Either someone who took part in or witnessed events created it, or it is itself the object of study: a diary, a photograph, a speech, a census record, a poem, a dataset, a lab notebook, an interview transcript. Anne Frank's diary is a primary source on Jewish life in hiding in the occupied Netherlands; Lincoln's Gettysburg Address is a primary source on how he framed the purpose of the Civil War in 1863.
A secondary source is one step removed. Its author did not experience the events or create the original work; they studied primary sources and wrote an interpretation, analysis or summary. A biography of Lincoln, a journal article comparing wartime diaries and a critic's essay on a poem are all secondary. They give you context and arguments to engage with, but they are someone's reading of the evidence, not the evidence itself.
A third category, tertiary sources, compiles and summarizes secondary work: encyclopedias, textbooks, dictionaries and databases of abstracts. They are useful for getting oriented and rarely what you should cite for a specific claim.
What counts as primary depends heavily on the field, because each field studies different kinds of evidence.
The science row trips people up most often. An article reporting an original experiment is a primary source, even though it is a polished, published document; a review article summarizing many such experiments is secondary. In law the distinction is about authority: primary sources are the law itself, and secondary sources explain or argue about it.
| Discipline | Primary source examples | Secondary source examples |
|---|---|---|
| History | Letters, diaries, government records, newspapers from the period, photographs, oral history interviews | Books and articles by historians interpreting the period |
| Literature | The novel, poem or play itself; the author's letters and drafts | Literary criticism, biographies of the author, introductions to scholarly editions |
| Natural sciences | Research articles reporting new experiments or observations; raw data | Review articles, textbooks, science journalism about a study |
| Social sciences | Survey data, interview transcripts, field notes, original empirical studies | Articles that synthesize or critique other studies |
| Law | Constitutions, statutes, regulations, court decisions | Law review articles, legal treatises, commentaries |
| Art and music | The painting, recording, score or performance itself | Art histories, critics' essays, exhibition catalogue essays |
The category is not a fixed property of a document; it depends on what you use it for. Thomas Carlyle's The French Revolution, published in 1837, is a secondary source about the revolution itself. But if your question is how nineteenth-century British writers remembered the revolution, the same book becomes a primary source — evidence of its own era's attitudes and anxieties.
The same logic applies elsewhere. A 1965 newspaper editorial about voting rights is secondary commentary on the legislation but primary evidence of public opinion in 1965. A film adaptation is secondary in relation to the novel and primary if you are studying adaptation. Always ask: am I studying this document as evidence in its own right, or using it as someone's interpretation of something else?
When the label is not obvious, work through these questions in order:
Step six settles it when the others conflict. Memoirs are a good example: written by a participant, so primary, but often decades later and shaped by hindsight, so they need some of the caution you would give an interpretation.
Most strong essays work from both directions. Primary sources supply the evidence you analyze yourself — the passage you close-read, the statistic you interpret, the letter that shows what someone believed at the time. Secondary sources show you what others have argued, so you can position your reading: agreeing, extending, or disagreeing with reasons.
A common weakness is letting secondary sources do the analysis for you, so the essay becomes a summary of what critics or historians think. Instead, present the primary evidence first, offer your own reading, and then bring in a secondary source to support, complicate or contrast with it. The guide to the PEEL paragraph method shows how to build each paragraph around a piece of evidence and your own explanation of it.
Treat primary sources critically too. A government report, a propaganda poster and a private diary can all be primary sources on the same war, and each had its own reasons to tell the story a particular way. The habits in the guide on evaluating a source apply to evidence from the past as much as to websites.
Primary sources are often easier to reach than students expect. Many national libraries and archives have digitized letters, newspapers, photographs and government documents that you can search online. University libraries hold special collections and subscribe to databases of historical newspapers and records. In the sciences and social sciences, primary sources are mostly original research articles, found through the same databases as other scholarly work; in law, official legislation and court websites publish the texts themselves.
Secondary sources come from library catalogues and scholarly databases, and the guide to finding credible sources covers that search in detail. One shortcut works for both: the footnotes and bibliography of a good secondary source are a ready-made list of the primary sources its author relied on.
Working at two levels — the document itself and what scholars say about it — means constant movement back and forth. In Cavua's Work space you can upload a primary text alongside the articles that discuss it and ask across them at once: “where does this critic's reading of the second letter depart from what the letter says?” Answers point to the page, so you go straight to the passage and judge for yourself.
If you are learning a whole subject, each course in the history catalogue comes with a 24/7 AI tutor you can video call, voice call or chat with, answering from that course's own syllabus and lessons. The catalogue is open to read without an account.
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A textbook is usually classed as a tertiary source, because it summarizes and organizes the findings of many secondary sources for teaching; some guides group it with secondary sources instead. Either way, it is rarely primary — unless your project studies textbooks themselves, for example how school history books presented a war in a particular decade.
It depends on the article. A research article reporting a new study, experiment or dataset is a primary source in the sciences and social sciences. A review article that summarizes and evaluates other studies is secondary. In the humanities, a journal article analyzing a novel or historical documents is secondary, because the novel or the documents are the primary sources.
Yes, when the person interviewed speaks from direct experience or is the subject of your study. An oral history with a veteran, or your own interview with a teacher for a project on classroom practice, is primary. An interview with a scholar commenting on events they did not witness is closer to a secondary source, since they are interpreting rather than reporting.
News reports written at the time of an event are usually treated as primary sources for that event, especially when they include eyewitness accounts or official statements. Analytical features and retrospective pieces written later are secondary. Old newspapers are also primary sources for studying the attitudes, language and priorities of their own period, whatever they were reporting on.
A tertiary source compiles or summarizes information from primary and secondary sources without adding new analysis. Encyclopedias, dictionaries, handbooks, textbooks, almanacs and bibliographies are typical examples. They are useful for background, definitions and finding key works, but most instructors expect you to cite primary and secondary sources for specific claims in academic writing.
Usually a documentary is a secondary source, because its makers select and interpret footage, interviews and records to tell a story about events. The archival footage and eyewitness interviews inside it can be primary material, though ideally you trace them to their original source. A documentary is primary if your project is about the film itself or how documentaries portray a subject.
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