Primary vs. secondary sources

A primary source is original or firsthand evidence. A secondary source interprets, summarizes or analyzes primary sources.

A primary source gives original evidence or a firsthand account: a diary, a letter, an interview, a legal document, a government record, or a report of original research. A secondary source works from primary sources. It summarizes, interprets or analyzes them: a biography, a textbook, a review article, a work of criticism.

Jane Austen’s letters are primary. A historian’s book analyzing what the letters say about her views is secondary.

The line depends on your field and your question. University library guides point out that an original research article is a primary source in the sciences and social sciences, but is generally treated as a secondary source in the humanities. The same newspaper story can be primary evidence of how an event was reported and secondary as an account of the event itself.

Why it matters for citing. Your instructor may ask for primary sources, or tell you not to rely on textbooks. When you cite a source you only found inside another one, cite what you actually read and say where the claim came from, following your style guide.

Some guides also describe tertiary sources, such as indexes, bibliographies and encyclopedias, which point you to primary and secondary ones.