What each citation style is actually doing

A citation style is often handled as an arbitrary formatting choice. It is not arbitrary. Each style evolved in a different scholarly tradition and encodes a different theory of what the citation is supposed to do for the reader. Picking the wrong one signals that the writer is unfamiliar with the conventions of the field they are writing in.

APA: "who, when"

Shape: (Smith, 2019) inline; full author-date reference list at the end.

Logic: In psychology and the social sciences, when a finding was established matters as much as what it claims. The field moves fast; a 2003 effect-size estimate and a 2023 one may disagree. APA puts the year on the page so the reader can gauge recency without flipping to the bibliography.

Used in: Psychology, education, nursing, public health, most behavioral sciences.

MLA: "where in the text"

Shape: (Smith 47) inline; alphabetical works-cited list.

Logic: In literary studies, the claim is usually about a specific passage. The year matters less; Moby-Dick is Moby-Dick. What matters is the page. MLA puts the page on the page.

Used in: Literature, cultural studies, linguistics, film, some philosophy.

Chicago (Notes and Bibliography): "where did this really come from"

Shape: Superscript footnote¹ pointing to a numbered note with a full first-use citation and short subsequent ones; bibliography at the end.

Logic: History often relies on archival sources, primary documents, personal correspondence, sometimes unpublished material. The footnote permits a very specific citation, such as "letter, Jefferson to Adams, 15 August 1812, Jefferson Papers, Box 7," without disrupting the prose.

Used in: History, art history, some religious studies. Also the default for scholarly monographs.

Chicago (Author-Date)

The same spirit as APA. Used in some sciences and in business writing where Chicago is house style but footnotes feel too heavy for the surrounding prose.

Harvard

A family of author-date styles close to APA, with per-institution variations. A university that says "use Harvard" almost always means a specific in-house style sheet. There are dozens.

IEEE

Numbered citations [7] inline; numbered reference list in citation order. Compressed and functional. Used in electrical engineering, computer science, and much of applied physics. The shape says: the reader will either trust the number or chase it; this is not literary prose.

Vancouver

Numbered like IEEE but ordered in the bibliography by first appearance. Standard in biomedical journals.

Practical advice

1. Check the target journal's style sheet first, not a general guide. Style guides drift; specific journal rules do not.
2. Do not mix styles within a manuscript. Half-APA, half-MLA papers are routinely desk-rejected.
3. Automate. Zotero, Mendeley, Paperpile, and Academe can render most common styles from the same source record. Manual formatting is appropriate only for archives, specialized presses, and house styles no tool supports.
4. Check the edition. APA 7 differs from APA 6 on substantive questions about pronoun use, citation of secondary sources, and the running head. The guide bought as a sophomore is the wrong one.

Academe handles the mechanics: pick a style, get a citation. The choice of style, and what it signals to a reviewer about where the work belongs, remains the author's call.