People sometimes ask why article titles and book titles in APA Style reference list entries are in sentence case capitalization rather than the title case capitalization that appears on those works. The answer takes us back to the 1929 origins of APA Style and a guideline that continues to have practical advantages today.
Bentley, M., Peerenboom, C. A., Hodge, F. W., Passano, E. B., Warren, H. C., & Washburn, M. F. (1929). Instructions in regard to preparation of manuscript. Psychological Bulletin, 26(2), 57–63. https://doi.org/10.1037/h0071487
In 1929, a seven-page article about preparing manuscripts for submission to APA journals was published in Psychological Bulletin. In this short article, the authors provided just one example of a journal article reference and one of a book reference—both included the title element in sentence case. Because articles and books were the primary types of works cited at the time, authors (creating references) and readers (reading reference lists) both likely benefited from having the title elements of those references appear with the same formatting.
As far as we can now discern, editors of the time also preferred sentence case for its readability and perhaps for reducing cost and space. Bentley et al. (1929) wrote that, in general, using too many capital letters “increases the cost of printing and disturbs the reader” (p. 58). In other words, sentence case is good for accessibility!
And readability of the title within a reference was particularly important because at times that could have been a researcher’s best and possibly only glimpse of the content of the cited works. To learn more about the cited works, a researcher would have needed to find the full text in print or to find abstracts by consulting another journal, Psychological Abstracts; but, not all psychological research could be covered by that journal and the coverage often lagged behind article publication dates (Benjamin & VandenBos, 2006). Moreover, “the early book coverage had been random and lacking in a systematic effort to cover the majority of the books published annually that were related to psychology” (Benjamin & VandenBos, 2006, p. 952). APA’s PsycInfo database, with abstracts and indexing, was not introduced until 1967, and full-text access to articles via URLs and DOIs was still many years away.
The sentence case guideline persisted in the first edition of the Publication Manual (1952) and continued through the seventh edition (2020). Sentence case for article and book titles is now well-established formatting that makes APA Style references readily recognizable (e.g., unique from MLA style, Chicago Manual style) and, to the original editors’ credit, reader friendly.
But “it’s always been this way” is not usually a satisfying answer! When considering updates for the seventh edition Publication Manual, the APA Style team considered many aspects of APA Style, including reference formatting. Some important guidelines about references were updated (PDF, 1.3MB), but keeping sentence case for titles within references had some practical positive benefits for today’s authors, readers, and copyeditors.
First, because accessibility was a primary focus in the seventh edition, the APA Style team agreed that sentence case for titles within references was more readable, especially because other details in a reference (author and source elements) tend to include mostly capitalized words. If you look for the sentence case element in a reference, you can quickly locate the work’s title, even though some titles are italicized and some are not (to learn more about why that is, see “A Tale of Two Reference Formats”). Any proper nouns in the title can also be better understood because their capitalization is noticeable when the other words in the title are mostly lowercase. As the 1929 article noted, titles were to have “no caps save for first word and proper nouns.”
What started with articles and books in 1929 was easy to extend to many other source types of works commonly cited today. The title element of an APA Style reference is capitalized consistently across document types, from journal articles and books to government reports, dissertations, podcast episodes, blog posts, data sets, webpages, and many more.
You can see these parallels by looking at the Title column in each template that precedes the reference categories in Sections 10.1–10.16 of Chapter 10 in the Publication Manual and in Sections 10.1–10.14 of Chapter 10 in the Concise Guide to APA Style. This consistency of style makes reference list entries easier for authors to create, easier for readers to parse, and easier for copyeditors to check and edit.
Benjamin, L. T., Jr., & VandenBos, G. R. (2006). The window on psychology’s literature: A history of psychological abstracts. American Psychologist, 61(9), 941–954. https://doi.org/10.1037/0003-066X.61.9.941