Chicago author-date vs notes-bibliography: which to use and how

The Chicago Manual of Style, now in its seventeenth edition published in 2017 with a digital update stream that runs roughly each year, is the reference for book and journal publishing in the United States. Almost every other style guide cribs from it on grammar and usage. Two facts confuse most students. The first is that "Chicago" actually means two completely separate citation systems. The second is that Kate Turabian's slimmer book, A Manual for Writers of Research Papers, Theses, and Dissertations, ninth edition, simplifies Chicago for student writers and is what your tutor probably assigned, even if they call it "Chicago." The two books agree on the rules.

The two systems at a glance

The notes-bibliography system uses superscript numbers in the text that point to footnotes (or endnotes) at the bottom of the page, plus an alphabetised bibliography at the end. The footnotes carry the full bibliographic detail the first time you cite a source and a shortened form for repeat citations. History, literature, theology, classics, and most of the humanities use notes-bibliography.

The author-date system looks more like APA. You put the author surname and year in parentheses inside your text, and you give the full reference once at the end in a list called "References." This is the system used in the social sciences and natural sciences when those fields choose Chicago over APA or Council of Science Editors style.

When to pick which

Look at the assignment brief first. Most tutors specify "Chicago notes" or "Chicago author-date" when they want one in particular. If the brief says only "Chicago," the safe default is notes-bibliography for any humanities paper and author-date for anything quantitative. Once you pick a system, do not mix. Switching between footnotes and parenthetical citations within the same paper is the single fastest way to lose marks in a Chicago essay.

Notes-bibliography has one practical advantage that humanities researchers value: footnotes can carry discursive content. You can explain a translation choice, note a manuscript variant, or point the reader toward a contrasting view without breaking the flow of the main argument. Author-date does not offer that affordance, which is part of why scientific writing tends to prefer it: in fields where discursive notes would be ornament, the cleaner in-text citation is faster to read.

Notes-bibliography: footnotes

A first-citation footnote contains the full bibliographic information separated by commas, with a final period. The author's name appears in normal order (first name first), the title of the book is italicised, the publisher and year go in parentheses, and the specific page or page range follows.

First note for a book:

1. Hilary Mantel, Wolf Hall (London: Fourth Estate, 2009), 47.

First note for a journal article:

2. Riya Patel, "Memory and Metaphor in Late Joyce," Modern Fiction Studies 65, no. 4 (2019): 615, https://doi.org/10.1353/mfs.2019.0033.

First note for a chapter in an edited book:

3. Sade Okafor, "Bilingual Word Recognition," in Handbook of Psycholinguistics, ed. Mona Cordoba and Tae Park (Cambridge: Cambridge University Press, 2019), 318.

For repeat citations, Chicago seventeenth edition encourages a short form rather than the older Latin abbreviations like "ibid." or "op. cit." The short form uses the author surname, a shortened title (the first few distinctive words, italicised for books and in quotation marks for articles), and the page number.

Short form for a repeat citation:

4. Mantel, Wolf Hall, 112.

5. Patel, "Memory and Metaphor," 620.

"Ibid." was retired from the official Chicago short-citation guidance in the seventeenth edition, though many tutors still accept it for back-to-back citations of exactly the same source.

Notes-bibliography: the bibliography

The bibliography appears at the end of the paper, alphabetised by author surname, with a hanging indent. The differences from a footnote are small but easy to mishit: in the bibliography, the author's surname comes first, elements are separated by periods rather than commas, and there are no parentheses around the publisher and year.

Mantel, Hilary. Wolf Hall. London: Fourth Estate, 2009.

Patel, Riya. "Memory and Metaphor in Late Joyce." Modern Fiction Studies 65, no. 4 (2019): 612-635. https://doi.org/10.1353/mfs.2019.0033.

For multiple works by the same author, replace the name in the second and later entries with a 3-em dash followed by a period, then continue with the title. Within an author's section, order entries alphabetically by title.

Author-date: in-text and reference list

The author-date system places the author surname and year of publication in parentheses inside your sentence, with a comma between the date and any page number.

The argument that working memory load drives reading comprehension (Patel and Liu 2021, 723) has been replicated several times.

If the author is named in the sentence, only the year and page sit in parentheses: Patel and Liu (2021, 723) found that the effect held across three age groups. For three or more authors, use the first author followed by "et al.": (Garcia et al. 2022, 14). Organisations as authors take the full name on first citation, then a shortened form thereafter.

The reference list goes at the end of the paper, headed simply "References," alphabetised, with a hanging indent. The year follows the author's name rather than coming after the publisher.

Patel, Riya, and Min Liu. 2021. "Working Memory Load and Reading Comprehension." Journal of Educational Psychology 113 (4): 720-734. https://doi.org/10.1037/edu0000512.

Mantel, Hilary. 2009. Wolf Hall. London: Fourth Estate.

Okafor, Sade. 2019. "Bilingual Word Recognition." In Handbook of Psycholinguistics, edited by Mona Cordoba and Tae Park, 312-340. Cambridge: Cambridge University Press.

Common formatting choices

Both systems share most of the small formatting choices. The text body is usually double-spaced, but footnotes are single-spaced with a blank line between notes. Page numbers go in the top right corner, except on the title page, which is unnumbered but counts as page i. A Times New Roman or similar serif font at 12 point remains the conservative default; Chicago does not mandate one. Block quotations are indented, single-spaced, and run for anything longer than about five lines of prose.

Numbers under 100 are spelled out in non-technical prose ("there were seventy-three respondents"), and figures are used for measurements, percentages, and quantitative text. Dates take the day-month-year format in running prose ("on 4 July 1776") because the Chicago Manual of Style recommends it as less ambiguous than the American month-day-year style, though American academic writing often uses the latter and tutors vary. Check your tutor's preference before submitting.

Quoting and block quotations

Short quotations sit inside your paragraph with double quotation marks. American Chicago style places commas and periods inside the closing quotation mark, even when those marks are not part of the quoted material; British Chicago, which Turabian also acknowledges, places them outside if they are not in the original. Check whether your tutor expects American or British conventions before submitting.

Block quotations are used for prose longer than about five lines, or for poetry of two or more lines. The block is indented half an inch from the left margin, single-spaced (with the surrounding paragraphs double-spaced), and carries no quotation marks. The citation, whether a footnote number or an author-date parenthetical, follows the closing punctuation rather than preceding it.

Numbers, dates, and abbreviations

Chicago is precise about numbers. Spell out numbers from one through one hundred in non-technical prose, and use figures for everything above. The same rule applies to ordinals: "fifth century" is spelled out, "the 21st century" uses figures (though some humanities writers prefer "the twenty-first century" for stylistic reasons). Numbers used with units of measurement or percentage always take figures: 5 km, 23 percent (or 23%, if your house style accepts the symbol).

Centuries are spelled out: "the nineteenth century" rather than "the 19th century." Decades may take either form: "the 1990s" or "the nineties," both acceptable so long as you choose one and apply it throughout. Do not use an apostrophe in plural decades: "the 1990s," not "the 1990's."

Abbreviations are introduced on first use with the full term, then used in the abbreviated form thereafter. Common Latin abbreviations like "e.g." and "i.e." are acceptable in parenthetical asides but should be avoided in running prose, where the English equivalents "for example" and "that is" read more naturally. Chicago avoids the older Latin abbreviations like "viz." and "cf." in general writing.

Online sources and DOIs

Chicago wants a stable URL for every online source, and a DOI is always preferred over a publisher URL because it survives website redesigns. Write DOIs as full URLs starting with https://doi.org/. Access dates are optional in most cases, but the Chicago Manual of Style recommends including them for sources that change over time or have no clear date of publication, such as a Wikipedia article or a research blog post.

For online news articles, name the publication, the date, and the URL. For a social media post, name the author, give the text of the post in quotation marks (up to about 160 characters), name the platform, give the date and time, and link to the post. Both systems share these conventions.

What to do next

Generate footnotes or reference entries with the Phrasit citation generator, check the readability of your prose with the reading level analyzer, and compare your draft against an earlier version using the text comparator.