Chicago Style: Notes and Bibliography or Author-Date

Being told to use Chicago is an incomplete instruction, and most people receiving it do not realise that. The Chicago Manual of Style documents two separate citation systems, and they produce visibly different papers. Before formatting anything, establish which one is required.

Chicago describes the split by discipline. Notes and bibliography cites sources in numbered footnotes or endnotes, each matching a superscript number in the text, usually with a bibliography as well. Chicago calls it their oldest and most flexible system, able to accommodate unusual sources that do not fit neatly elsewhere, and it is preferred by many working in the humanities, including literature, history, and the arts. Author-date cites sources parenthetically in the text by author surname and year, matched to a reference list. Because it credits researchers by name while emphasising the date, it is preferred by many in the sciences and social sciences.

• Notes and bibliography: superscript number in the text, full details in a footnote or endnote, usually plus a bibliography.
• Author-date: (Shannon 1948, 379) in the text, full details in a reference list.
• History, literature, art history, theology: expect notes and bibliography.
• Sciences, social sciences, and most empirical work: expect author-date.
• If the assignment or journal does not say, ask. Guessing produces a paper formatted in the wrong system, which is a rewrite rather than a correction.

A superscript number goes in the text, after the punctuation. The matching note carries the full source details the first time it appears, and a shortened form on every later appearance. A bibliography at the end lists the sources alphabetically.

The note and the bibliography entry are not the same string. A note reads as running prose: the author's name in normal order, elements separated by commas, publication facts in parentheses, and a colon before the specific page cited. A bibliography entry reads as a list item: surname first for alphabetising, elements separated by full stops, and the full page range rather than one page.

1. Place the superscript number after the sentence's closing punctuation.
2. Give the full details in the first note for that source.
3. Use the shortened form afterwards: author surname, short title, page.
4. Alphabetise the bibliography by author surname, with a hanging indent.
5. Check that every source discussed substantively appears in the bibliography, even where the notes alone would carry the citation.

The in-text citation gives the author surname and the year, with the page after a comma when you are pointing at a specific passage: (Shannon 1948, 379). No p. or pp. appears. The reference list entry moves the year forward to sit immediately after the author, which is the quickest way to tell an author-date reference list from a Chicago bibliography at a glance.

• Parenthetical: (Shannon 1948, 379). Comma before the page, no p.
• Named in the sentence: Shannon (1948, 379) argued that...
• Two authors: (Tversky and Kahneman 1974). Chicago spells out and.
• Three or more authors: (Jumper et al. 2021) in the text, while the reference list names them all.
• Two works by one author in one year: append letters, as in (Shannon 1948a).
• The reference list is alphabetical by surname, with the year directly after the author.

The clearest way to see the difference is to watch a single record change shape. The punctuation is doing the work, and this is where hand-typed references go wrong.

• Note: the author's name in normal order, commas throughout, publication details in parentheses, a colon before the page cited.
• Bibliography: surname first, full stops between elements, the complete page range.
• Author-date reference list: surname first, then the year, then the rest.
• The shortened note drops everything but surname, short title, and page.

Chicago is a large manual and most of it will not apply to a given paper. These are the questions that recur.

• Which edition: the eighteenth is current. Departments sometimes still specify the seventeenth, and the difference matters for details, so confirm rather than assume.
• Titles: headline-style capitalisation for titles of works. Article and chapter titles take quotation marks; books and journals are italicised.
• Page ranges: Chicago abbreviates the second number in a range according to its own rules, so 379-423 stays full while 100-104 contracts to 100-104 only where the manual allows. When unsure, write the range in full rather than contracting it wrongly.
• DOIs and URLs: include a DOI where one exists, as a https://doi.org/ address. Use a URL only where there is no DOI.
• Access dates: not required for most published sources. Include one where the content is undated or liable to change.
• Footnotes or endnotes: either is acceptable in notes and bibliography. Follow the venue's preference, and be consistent.