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

Chicago style is not a single citation system. It is two — and the choice between them is not a matter of preference. It is a disciplinary and institutional determination that should be made before the first citation is formatted and that, if made incorrectly, will require a complete reformatting of the documentation apparatus before the manuscript is ready.

Understanding the two systems and when each applies is foundational to working in Chicago style.

Notes-Bibliography (NB) is the system used in the humanities — history, literature, philosophy, art history, religious studies, and related fields. It uses footnotes or endnotes for citations, with a bibliography at the end of the document listing all cited sources. Notes in the NB system serve two functions simultaneously: they provide the citation information and they provide space for substantive commentary, qualification, and additional sourcing that the author does not want to interrupt the main text to include. This dual function is one of the reasons the NB system is favored in humanities disciplines, where 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. The AD system is more compact than the NB system and is better suited to 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 rather than being relegated to the bibliography.

Choosing the right system requires knowing which system your discipline uses, which system your institution requires, and — where the two are not identical — how to resolve the discrepancy. Most humanities dissertations use NB. Most social science dissertations use APA, which is a separate system entirely, though Chicago AD is used in some social science fields. The specific requirement should appear in the dissertation manual of the institution, and 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. This happens most often with authors who are working from a model dissertation or a previous advisor's manuscript that used a different system, or with authors who have formatted citations from memory rather than from the current edition of the manual.

A note on edition. The current edition of the Chicago Manual of Style is the 17th, published in 2017. Authors working from earlier editions — or from style guides based on earlier editions — may be applying conventions that have been revised. The 17th edition made several significant changes to digital source formatting, DOI presentation, and the treatment of online-only publications, and those changes are frequently not reflected in older institutional style guides.

The documentation system is the scaffolding of the scholarly argument. Getting it right from the beginning is easier than reformatting it after the manuscript is otherwise complete — and considerably less disruptive to the revision process.