Primary and secondary sources: differences and citations

What distinguishes primary and secondary sources

A primary source reports original content. A secondary source describes, summarizes, or cites information that first appeared in another work.

The distinction does not depend only on format. A research article that first reports a study's results is a primary source for those findings. A review article that compares previous studies is a secondary source in relation to those studies.

APA Style recommends reading and citing the primary source whenever possible. Doing so lets you see the complete explanation, understand its limitations, and prevent an idea from reaching your paper through several layers of interpretation.

Examples of primary and secondary sources

What your paper needs	Possible primary source	Possible secondary source
Explain a study's findings	Article that reports the original results	Textbook that summarizes the study
Analyze a person's words	Published interview or recorded speech	News article that comments on the interview
Study a historical event	Letter, diary, photograph, or contemporary record	Book that interprets those records
Explain a theory	Work in which the theory was proposed	Encyclopedia or handbook that summarizes it
Discuss a law or court decision	Official legal document	Article that explains its effects

The same work may serve different roles depending on your question. A news report could be a primary source for studying how a media outlet framed an event and a secondary source for learning about research that it merely summarizes.

Which source to cite

Cite only works you actually read. When you consulted the original work, cite it directly. You do not need to mention the textbook, article, or lecture that helped you discover it unless you also use that second source's own analysis.

If you first encounter a study in a class, handbook, or encyclopedia, look for the original publication before drafting. A secondary source may simplify a finding, omit a limitation, or interpret it for a different purpose.

When to use a secondary source citation

Use secondary source citations sparingly. One may be necessary when the original work:

• is out of print or otherwise unavailable;
• cannot be retrieved through an accessible library or archive;
• is available only in a language you cannot understand;
• is known through a historical document whose original source no longer exists.

Do not use as cited in merely to avoid consulting an available work. First check your library catalog, academic repositories, and the reference details supplied by the secondary source.

How to cite a secondary source

In the text, identify the primary source and then name the work you actually read with the words as cited in.

Parenthetical citation:The source is identified in parentheses, normally with the author and year: (Perez, 2024).

(Rabbitt, 1982, as cited in Lyon et al., 2014)

Narrative citation:The author is part of the sentence and the year appears in parentheses: Perez (2024).

Rabbitt (1982, as cited in Lyon et al., 2014) proposed that...

When the year of the primary source is unknown, omit it:

Allport's diary (as cited in Nicholson, 2003) describes...

In the reference list, include only the secondary work you read. In these examples, that would be Lyon et al. (2014) or Nicholson (2003). Do not add a reference for Rabbitt or Allport as though you had consulted those works.

Complete example

Suppose you read an illustrative book by Castillo (2023) that summarizes a proposal published by Ramirez in 1998, but you cannot retrieve the original document.

In the text:

Ramirez (1998, as cited in Castillo, 2023) connected planning with the ability to recognize gaps in an argument.

In the reference list:

Castillo, M. (2023). Processes of academic writing. Horizon Press.

The reference identifies Castillo because that is the work you read. Ramirez appears only in the in-text citation to credit the origin of the idea.

Common mistakes

• Adding both works to the reference list: include only the source you read.
• Citing only the primary source: this suggests that you consulted a work you did not see.
• Using a secondary source when the original is available: locate and cite the original publication.
• Confusing a review with the original research: check where the data were collected or the proposal first appeared.
• Copying a secondhand quotation without checking it: try to find the original wording. If it is unavailable, make clear that you encountered it through another work.

Checklist

Before finishing, check that:

• you identified which work contains the original contribution;
• you tried to locate and read that source;
• you used as cited in only when the original was unavailable;
• you named the primary source in the text;
• you added only the work you read to the reference list;
• the secondary source's author and year match its reference.