Primary and secondary sources: definitions and examples

Research assignments often say "use at least two primary sources," and many students are not sure what counts. The difference matters for more than the rubric. Primary sources let you look at the evidence yourself and draw your own conclusions; secondary sources show you what experts have already made of that evidence. Strong research papers use both.

What is a primary source?

A primary source is original material created at the time you are studying, or by someone who took part in or witnessed what it describes. It is the raw evidence: letters, diaries, speeches, interviews, photographs, government records, maps, objects, laws, court decisions, original data and creative works. In the sciences, a primary source is the article in which researchers first report their own experiment or study, including their methods and results.

What is a secondary source?

A secondary source is created later by someone who did not experience the events firsthand. It describes, analyzes, compares or interprets primary sources. Biographies, history books, documentaries, literary criticism, review articles and news analysis are secondary sources. A secondary source is one step removed from the evidence. It gives you an expert's reading of the material, which is valuable, but you should check it against the material itself when you can.

What is a tertiary source?

Tertiary sources collect and condense primary and secondary sources: encyclopedias, dictionaries, almanacs, handbooks and many introductory textbooks. They are good for background reading and for finding search terms, but most college instructors do not want them cited as evidence in a research paper. Use them to get your bearings, then follow their references to the secondary and primary sources behind them.

Primary vs. secondary sources: comparison

Examples by subject

It depends on your research question

The same document can be primary in one project and secondary in another. A geography textbook from 1960 is a secondary source about the world's rivers, but it becomes a primary source if your paper asks how schools taught geography in 1960. A film review is secondary when you study the film, but primary when you study how critics reacted when the film came out. The test is simple: is this document the thing you are studying, or someone's commentary on the thing you are studying?

Is a newspaper article primary or secondary?

It depends on when and how it was written. A news report written at the time by a reporter on the scene is usually treated as a primary source for that event, especially in history papers. An article written years later, or one that pulls together and analyzes other reports, is secondary. Opinion columns are primary sources for what people thought at the time and secondary sources for the events they comment on.

How to tell which kind of source you have

1. Check the date. Was it created during the period you are studying, or later?
2. Check the creator. Did the author take part in, witness or directly measure what is described?
3. Check the content. Does it present raw evidence (data, testimony, original words), or does it summarize and interpret other sources?
4. Check the structure. A research article with a methods section describing the authors' own study is primary; an article that mostly discusses other studies is secondary.
5. Ask how you will use it. If you analyze it as evidence, it is a primary source for your paper.

Where to find primary sources

• Your library's digital collections and archives, including old newspapers, photographs and letters.
• Government websites for laws, statistics, census tables and official reports.
• Museum and historical society collections, many of which have put items online.
• Scholarly databases, searched for original research articles rather than reviews.
• Published collections of letters, diaries or speeches, and oral history projects.
• Your own fieldwork, such as interviews, surveys or observations, if your assignment allows it.

How to use both kinds in a paper

Secondary sources give you background, show you what scholars already think and help you shape a thesis statement. Primary sources let you test those ideas against the evidence and add details no textbook has. A useful pattern for a body paragraph: state your point, support it with primary evidence, then show how a secondary source confirms, explains or challenges your reading. Cite both kinds every time you use them (see how to avoid plagiarism), and check each one with the credible sources questions.

Common mistakes

• Assuming anything old is primary. A biography written in 1920 about someone who lived in the 1780s is still secondary for that person.
• Assuming anything online is secondary. A digitized letter is still a primary source.
• Counting an encyclopedia entry as one of your required secondary sources.
• Quoting a primary source you saw only inside a secondary book without saying so. If you cannot see the original, cite it as quoted in the book.
• Treating a review article in science as original research. Reviews summarize other studies.