How to Cite a Secondary Source: "As Cited In" in APA, MLA, Chicago, and Harvard

A secondary source citation, also called an indirect citation, credits a quotation or idea that you found in one work but that first appeared in another. Say you read Daniel Ashworth's 2019 book, and Ashworth quotes a 1974 article by Ruth Okafor that you never saw. Your citation has to show two things: the words are Okafor's, and you know them only through Ashworth.

This is a different problem from a quote within a quote. That term is about punctuation. The passage you quote already contains a quotation, and you have to mark both levels. A secondary citation is about where you found the material.

The table uses one invented pair of sources. Ruth Okafor's 1974 article is quoted on page 52 of Daniel Ashworth's 2019 book Literacy at Work. Ashworth's book is the only one you have read. All four styles italicize book and journal titles. The table shows them in plain text.

• APA 7: list only the work you read. If the original's year is unknown, Douglas College's APA guide says you can leave it out of the in-text citation.
• MLA 9: Works Cited names Ashworth, not Okafor. Douglas College's MLA guide, citing the MLA Handbook, says you can drop "qtd. in" when your sentence already makes clear that the source is secondhand.
• Chicago: the note names both works. For the bibliography, Wellesley College's guide (17th edition) lists only the secondary source, while McGill's 18th-edition guide lists both. Ask your instructor which version they expect.
• Harvard: University College Dublin's guide uses "cited in" or "citing" and gives full details only for the secondary source. Harvard guides differ between institutions, so use the one your school names.

APA's guidance, as summarized in Douglas College's APA guide, is to cite secondary sources sparingly. Its examples are an original that is out of print, unavailable, or available only in a language you do not understand. Douglas College's MLA guide and UCD's Harvard guide both send you to the original whenever you can get it. Chicago is blunter. Its official Q&A discourages "quoted in" citations because "authors are expected to have examined the works they cite."

1. Start with the secondary source's reference list. It gives you the author, title, year, and often a DOI or page range. Copy those details exactly.
2. Search your library catalog and databases by the exact title, not only by keywords.
3. If your library does not hold it, request it through interlibrary loan. Ask how long delivery takes before you plan around it.
4. For older books, look for a scanned edition in a digital library. For articles, check the author's institutional repository.
5. Ask a subject librarian when the reference is incomplete or the title changed between editions.

Once you have the original, cite it directly and drop the secondary citation. Take the quoted words and the page number from the original, not from what the secondary source printed. The two do not always match.

A secondhand quotation is only as accurate as the person who passed it on. Jergas and Baethge's 2015 systematic review and meta-analysis in PeerJ examined quotation accuracy in medical journal articles. Of 559 studies screened, 28 were included in the main analysis. The authors estimated a major quotation error rate of 11.9 percent (95% CI 8.4 to 16.6), a minor error rate of 11.5 percent (95% CI 8.3 to 15.7), and a total quotation error rate of 25.4 percent (95% CI 19.5 to 32.4). In their definition, a major error is a quotation that is not at all in accordance with the citing authors' claim. Some of the included studies scored a citation to a secondary source as a minor error in itself. Such indirect references made up less than one sixth of all quotation problems. The authors still consider them problematic, in part because errors can easily spread from one paper to the next. The review covered medicine only. Still, if you rely on someone else's reading of a source, you take on any mistake in it.

A secondary citation also does not let you borrow the secondary author's prose. If your account of Okafor follows Ashworth's sentences, your text overlaps with Ashworth's book. It needs quotation marks or a genuine rewrite, with Ashworth credited. Our guide on when paraphrasing becomes plagiarism shows where that line falls, and how to cite a paraphrase covers the format. Citing Okafor as if you had read her is a separate problem. Our guide to what plagiarism is lists citing a source you never read under source-based plagiarism.

Before you submit, run the draft through the Certentis plagiarism checker. Its report highlights passages that match sources it finds, so you can see where a secondary author's phrasing survived and still needs quotation marks or your own wording. A report may not find every source, so also compare your quotations with your notes.