What Is a Secondary Source?
A secondary source is a work that describes, analyzes, interprets or summarizes information from primary sources or other research. It is one step removed from the original evidence. Examples include history books, journal articles that review earlier studies, biographies, critical essays, documentaries and most textbooks.
What secondary sources do
- Provide context and background on a topic.
- Interpret evidence and offer arguments about what it means.
- Summarize research, helping you see what is known.
- Compare views, showing debates between scholars.
- Point to other sources through references and bibliographies.
In a literature review, secondary sources are the core of the discussion, and in most essays they support or challenge your argument.
Primary, secondary and tertiary
| Type | Role | Examples |
|---|---|---|
| Primary | Original evidence | Letters, data, original experiments, works of art |
| Secondary | Analysis or interpretation of primary evidence | Review articles, scholarly books, critiques |
| Tertiary | Collections or summaries of primary and secondary sources | Encyclopedias, handbooks, indexes |
Classification can change with the question. A history of medicine written in 1900 is a secondary source about earlier medicine, and a primary source about attitudes in 1900.
Evaluating secondary sources
- Author: what are the credentials and expertise?
- Publisher: is it a university press, reputable academic publisher or journal?
- Peer review: was it reviewed by experts?
- Evidence: does it cite its sources and explain its methods?
- Date: is it current, or has newer research changed the picture?
- Bias and purpose: does the author or publisher have an agenda?
- Reception: how do other scholars respond?
Using them in your writing
Do not rely on a single secondary source. Compare several, and note where they agree and disagree. Use them to build context, support your analysis and place your argument within the field. Paraphrase accurately, quote sparingly and cite properly. Avoid using one author's summary as a substitute for reading important primary material, especially for key claims.
Finding them
Start with library databases and subject guides. Search by keywords, and use filters for scholarly and peer-reviewed sources. Follow reference lists in useful articles to find others. Ask a librarian for help.
Why it matters
Secondary sources show how experts have interpreted the evidence, and they help you build on existing work instead of starting from scratch.
Related terms
See primary source, peer review, scholarly journal, bibliography and gray literature.
Frequently asked questions
What is an example of a secondary source?
A history book about the Second World War, a review article summarizing studies, a biography, a documentary or a critical essay on a novel.
Are textbooks secondary or tertiary sources?
Often secondary or tertiary, since they summarize and synthesize research by others. Encyclopedias and dictionaries are usually called tertiary.
How do I know if a secondary source is reliable?
Check the author's expertise, the publisher, whether it was peer reviewed, whether it cites evidence, its date and whether other experts support its claims.