Primary sources are firsthand evidence: documents, data, objects and accounts created by the people who took part in or witnessed what you are studying, usually at the time. A letter, a diary, a speech, a survey dataset, a court decision and the novel you are analyzing are all primary sources. Secondary sources are later accounts that describe, analyze or interpret primary sources, such as a history book, a biography, a review article or a work of literary criticism. Tertiary sources, like encyclopedias and most textbooks, summarize the other two.
Which kind a source is depends on your question, not on the document alone. A review of The Great Gatsby printed in 1925 is a primary source if your paper asks how the novel was received when it came out: the review is that reception. If your paper asks what the novel means, the same review is a secondary source, one early reader's interpretation, and the novel itself is your primary source. The table below sorts the three kinds; the examples by field and the section on the gray zone help you decide for the source on your desk.
The three kinds at a glance
| Kind | What it is | Examples | Use it to |
|---|---|---|---|
| KindPrimary | What it isFirsthand evidence, created at the time or by participants and witnesses | ExamplesLetters, diaries, speeches, photographs, interviews, datasets, original research articles, laws, court decisions, the novel or painting you analyze | Use it toBuild your argument on evidence |
| KindSecondary | What it isA later account that analyzes or interprets primary sources | ExamplesScholarly books and articles that analyze, biographies, review articles, criticism, documentaries made afterward | Use it toSee how others read the evidence and where the debate stands |
| KindTertiary | What it isA summary or index of primary and secondary sources | ExamplesEncyclopedias, dictionaries, handbooks, most textbooks, bibliographies, Wikipedia | Use it toGet background, vocabulary and leads to better sources |
What is a primary source?
A primary source is as close to the thing itself as you can get. It was made by someone who saw it, did it, measured it or lived through it, and no later interpreter has reworked it, though it still carries its maker's point of view. Most primary sources fall into a few families:
- Records and documents: government records, census returns, minutes, contracts, ship manifests, maps, court filings.
- Personal writing: letters, diaries, journals, memoirs and autobiographies, emails and social media posts.
- Creative works, when the work itself is your subject: novels, poems, plays, films, paintings, songs, buildings.
- Original research: articles that report a new experiment, survey or observation for the first time, along with the datasets, lab notebooks and field notes behind them.
- Media from the time: newspaper reports, photographs, radio broadcasts, newsreels, speeches as delivered.
- Interviews and oral histories with people who took part in the events.
- Objects: tools, clothing, coins, posters, tickets, anything made or used in the period.
A primary source does not have to be old, and it does not have to be written at the moment of the event. A memoir written fifty years later is still a primary source on its author's life, because the author was there. What matters is how close the creator stood to what you are studying, not only the date on the page.
Primary doesn't mean more reliable. A diary records one person's view, a press release is written to persuade, and a newspaper report filed the night of an event can get the facts wrong. “Primary” describes where a source stands in relation to your question, not how far to trust it; the section on evaluating a source covers that.
What is a secondary source?
A secondary source is one step removed. Its author works from primary sources, often many of them, and adds something they do not contain on their own: an interpretation, a comparison, a cause, a judgment. A historian reading a thousand letters from Civil War soldiers and arguing about why they kept fighting has written a secondary source. So has a critic explaining how Frankenstein (1818) uses its letter-and-story frame, or a scientist summarizing twenty years of trials in a review article.
Secondary sources are how you learn what is already known and argued about your topic. They give context, they point to primary sources in their notes and bibliographies, and they show you the positions your own argument has to answer. Two habits keep them honest. Cite a secondary source for its interpretation, not for a fact you can check in the original. And when a secondary source quotes a primary one, trace the quotation back and read it in context before you rely on it.
What are tertiary sources?
Tertiary sources compress and organize the other two: encyclopedias, dictionaries, almanacs, handbooks, chronologies, most textbooks, subject guides and Wikipedia. They are the fastest way into an unfamiliar topic. Read one to learn the names, dates and terms you need, then use its references to find the primary and secondary sources it was built from. If you're writing about the 1918 influenza pandemic, for example, an encyclopedia entry gives you the dates, the places hit hardest and the terms historians use, and its reference list points to the histories (secondary) and the newspapers and public health records (primary) you can actually cite. Many instructors don't accept tertiary sources as evidence in a research paper, so treat them as the map, not the destination.
Examples by field
Every discipline has its own primary materials. In law the usual terms are primary authority (the law itself) and secondary authority (commentary on it), but the idea is the same.
| Field | Primary sources | Secondary sources |
|---|---|---|
| FieldHistory | Primary sourcesLetters, diaries, speeches, newspapers from the period, government records, maps, photographs, artifacts | Secondary sourcesHistory books, journal articles about the period, biographies, documentaries made later |
| FieldLiterature | Primary sourcesThe novel, poem or play; drafts and manuscripts; the author's letters and interviews | Secondary sourcesLiterary criticism, biographies of the author, introductions to scholarly editions, later reviews |
| FieldNatural sciences | Primary sourcesArticles reporting original experiments or observations, datasets, lab notebooks, preprints, patents | Secondary sourcesReview articles, most meta-analyses, books and essays that explain or assess research |
| FieldSocial sciences | Primary sourcesSurvey responses, census and government statistics, interview transcripts, field notes, original studies | Secondary sourcesAnalyses of other researchers' data, literature reviews, books that synthesize studies |
| FieldJournalism | Primary sourcesInterviews, eyewitness accounts, documents, court filings, recordings, an organization's own statement | Secondary sourcesOther outlets' reporting, analysis and commentary on the event |
| FieldLaw | Primary sourcesConstitutions, statutes, regulations, court decisions | Secondary sourcesLaw review articles, treatises, legal encyclopedias, the Restatements of the Law |
| FieldArts and music | Primary sourcesPaintings, recordings, scores, performances, sketchbooks, artists' statements | Secondary sourcesArt and music criticism, exhibition and concert reviews, art history books |
| FieldBusiness | Primary sourcesAnnual reports, financial filings, internal memos, sales and market data | Secondary sourcesAnalyst reports, business journalism, case studies written afterward |
The science row trips people up. Journal articles are not all one kind: an article with its own methods and results is primary, while a review article that summarizes many studies is secondary, even when both are peer reviewed. Look for a methods section and new data. A paper organized in IMRaD format, with its own methods and results, is usually primary research.
The gray zone: one source, two roles
Sorting is easy for a diary or an encyclopedia. It gets interesting when a source sits between the two, and the honest answer is "it depends on what you're asking". These cases come up in almost every research assignment:
| Source | Primary when you study… | Secondary when you study… |
|---|---|---|
| SourceA 1955 American history textbook | Primary when you study…How schools in the 1950s taught Reconstruction | Secondary when you study…Reconstruction itself |
| SourceA newspaper report from April 1912 on the Titanic | Primary when you study…What the public was told and believed that week | Secondary when you study…Exactly how the ship sank; survivor testimony to the 1912 inquiries is closer evidence |
| SourceA 1925 review of The Great Gatsby | Primary when you study…How the novel was received when it came out | Secondary when you study…The novel's meaning, where your own reading of the text comes first |
| SourceA biography of Frederick Douglass | Primary when you study…How historians have portrayed Douglass over time | Secondary when you study…Douglass's life, where his own 1845 Narrative is the primary source |
| SourceYour interview with a historian of the 1918 flu | Primary when you study…The historian's views and methods | Secondary when you study…The pandemic itself, which the historian did not witness |
| SourceA politician's social media post | Primary when you study…The politician's words, strategy or reception | Secondary when you study…The events the post describes, until you confirm them elsewhere |
The pattern: a source is primary for the people and the moment that produced it. Whenever your question moves past what its creator could see or know, the same source becomes someone's account of events, and you should look for evidence closer to them.
How to tell them apart
Ask these in order and you can sort almost any source in a minute.
- Who made it, and were they there?
A participant, a witness or the researcher who ran the study points to primary. Someone working from other people's records points to secondary.
- When was it made?
At the time, from later memory, or long afterward from other sources. The first two can be primary; the third almost never is.
- Does it report evidence or interpret it?
New data, observations or testimony are primary. Analysis, comparison and argument built on other sources are secondary. A long reference list is often the giveaway.
- What is your research question?
Hold the source up against the question. If the source is the thing you are investigating, it is primary for your paper, whatever it would be for someone else's.
For a second opinion on a hard case, attach your notes on the source, or a transcribed letter, and ask the Strokes Assistant how it would classify the source for your research question, and why. Then check its reasoning against the four questions above.
Which sources your assignment needs
Assignments rarely say "use only primary sources", but most have a mix in mind. These are the usual expectations:
- History papers rest on primary sources, with secondary sources to show how historians have read them.
- Literature essays treat the text as the primary source and often require a set number of critical sources.
- Science and social science papers cite primary research articles for findings and review articles for background.
- Literature reviews read the primary studies on a question and become a secondary source themselves.
- Theses and dissertations combine your own primary material, such as data, interviews or archive work, with a full account of the secondary literature.
If you are still choosing what to write about, the research paper topics list includes questions with good primary material behind them, and the research question examples show how to narrow one until you know which sources will answer it.
Where to find primary sources
Start with your own library: its catalog, its subject databases and its special collections, where the archives and rare materials are. Librarians know which collections fit your topic. Beyond that, these digital collections are free to search:
| Collection | What you'll find |
|---|---|
| CollectionLibrary of Congress | What you'll findManuscripts, photographs, maps, recordings, and Chronicling America, its database of digitized historic US newspapers |
| CollectionUS National Archives | What you'll findFederal records, from treaties and military service files to census schedules, in the National Archives Catalog |
| CollectionFounders Online | What you'll findThe letters and papers of Washington, Franklin, Adams, Jefferson, Hamilton and Madison |
| CollectionHathiTrust Digital Library | What you'll findMillions of digitized books and journals from research libraries, with public-domain volumes in full view |
| CollectionInternet Archive | What you'll findDigitized books, films and recordings, plus the Wayback Machine's snapshots of old web pages |
| CollectionProject Gutenberg | What you'll findFree public-domain books, for the literary texts themselves |
| CollectionDigital Public Library of America and Europeana | What you'll findSearch across the collections of American and European libraries, archives and museums |
| CollectionPubMed and arXiv | What you'll findCitations and abstracts of biomedical research, many with free full text (PubMed), and preprints in physics, mathematics, computer science and more (arXiv), which are not peer reviewed |
How to evaluate a source
Knowing what kind of source you have is half the work. The other half is deciding how far to trust it. Two checklists are widely taught: the CRAAP test (currency, relevance, authority, accuracy and purpose), created at California State University, Chico's Meriam Library in 2004, and SIFT (stop, investigate the source, find better coverage, trace claims to their origin), promoted by Mike Caulfield for checking sources online. For primary sources, add questions about the person behind the document:
When you write up what you found, an annotated bibliography is a good place to record each verdict. The APA annotated bibliography example shows annotations that say what each source is good for and where it is weak.
Frequently asked questions
Is a textbook a primary source?
Usually not. A textbook summarizes other people's research, so most library guides class it as a secondary or tertiary source. It becomes a primary source only when the textbook itself is what you are studying, for example how American history textbooks of the 1950s described Reconstruction.
Is an interview a primary source?
Yes, when the person speaks from firsthand experience: a survivor, a witness, a participant, the scientist who ran the study. An interview with an expert about events they did not witness is a primary source for the expert's own views and a secondary source for the events themselves.
Are newspaper articles primary or secondary sources?
News reports written at the time are usually treated as primary sources for the period, because they show what people knew and were told. An article written years later looking back at an event is secondary. Opinion pieces are primary sources for the writer's views.
Can a book be a primary source?
Yes. A novel you are analyzing, a memoir, a diary published as a book, a collection of letters or a book reporting an author's own original research are all primary sources. A book that interprets other people's evidence, such as most history books and biographies, is secondary.
