Bibliography vs. Author-Date: Choosing the Right CMOS Pathway for Your Project

Chicago style contains two citation systems. Choosing between them is a disciplinary and institutional determination that belongs before the first citation is formatted, because a wrong choice means a complete reformatting of the documentation apparatus before the manuscript is ready.

Notes-Bibliography (NB) is the system used in the humanities (history, literature, philosophy, art history, religious studies, and related fields), and it uses footnotes or endnotes for citations, with a bibliography at the end of the document listing all cited sources. NB notes do two jobs. They carry the citation information, and they give the author room for substantive commentary, qualification, and additional sourcing that would otherwise interrupt the main text. That double duty is one reason humanities disciplines favor the system, since the relationship between a claim and its evidentiary basis is often complex enough to require annotation.

Author-Date (AD) is the system used in the social sciences and some natural sciences. It uses parenthetical in-text citations — author last name and year of publication — with a reference list at the end of the document. AD is more compact than NB. It also suits fields where the currency of a source is a primary criterion of its authority, which is why the year of publication appears in every citation instead of waiting in the bibliography.

Choosing the right system requires knowing which system your discipline uses, which system your institution requires, and how to resolve the discrepancy where the two differ. Most humanities dissertations use NB. Most social science dissertations use APA. That is a separate system entirely, though Chicago AD is used in some social science fields. The specific requirement should appear in the institution's dissertation manual; when it does not, the department's graduate handbook or the dissertation committee chair is the authoritative source.

The most common error is the use of NB formatting conventions, particularly footnote citation style, in a document that should be using APA or Chicago AD. Model dissertations are a frequent source. An author working from one, or from a previous advisor's manuscript that used a different system, inherits its conventions; so does an author who formats citations from memory without checking the current edition of the manual.

A note on edition. The current edition of the Chicago Manual of Style is the 18th, published in 2024. Authors working from earlier editions, or from style guides based on them, may be applying conventions that have since been revised. The 17th edition, published in 2017, made significant changes to digital source formatting, DOI presentation, and the treatment of online-only publications, and the 18th revised the manual again. Older institutional style guides often miss these changes. Check which edition your institution or publisher requires.