Citation styles look like arbitrary punctuation until you put them side by side. Then a pattern appears: each style puts first what its readers care about most. Psychologists want to know how recent a finding is, so APA puts the year right after the author. Literary scholars quote passages, so MLA puts the page number in the text and leaves the year near the end. Historians lean on footnotes, so Chicago gives you a full note at the bottom of the page and a bibliography at the end. This article cites the same two sources in each style, explains why they differ, and lists the mistakes markers see most. Every example was produced with the citation generator, which you can use to check your own.
The two sources
- A book: Daniel Kahneman, Thinking, Fast and Slow, published by Farrar, Straus and Giroux in 2011.
- A journal article with four authors: Angela L. Duckworth, Christopher Peterson, Michael D. Matthews and Dennis R. Kelly, "Grit: Perseverance and passion for long-term goals", Journal of Personality and Social Psychology, volume 92, issue 6, pages 1087–1101, 2007, DOI 10.1037/0022-3514.92.6.1087.
APA 7th edition
Reference list:
Kahneman, D. (2011). Thinking, fast and slow. Farrar, Straus and Giroux. Duckworth, A. L., Peterson, C., Matthews, M. D., & Kelly, D. R. (2007). Grit: Perseverance and passion for long-term goals. Journal of Personality and Social Psychology, 92(6), 1087–1101. https://doi.org/10.1037/0022-3514.92.6.1087
In the text: (Kahneman, 2011, p. 45) or "Kahneman (2011) argues…"; (Duckworth et al., 2007).
What to notice: initials instead of given names; an ampersand before the last author; the year in brackets straight after the authors; sentence case for the book and article titles (only the first word, the first word after a colon and proper nouns capitalised); the journal name and the volume number in italics, the issue in brackets and not italic; the DOI written as a full https://doi.org/ link. APA lists up to 20 authors in the reference list, and in the text uses "et al." as soon as there are three or more.
MLA 9th edition
Works cited:
Kahneman, Daniel. Thinking, Fast and Slow. Farrar, Straus and Giroux, 2011. Duckworth, Angela L., et al. "Grit: Perseverance and Passion for Long-Term Goals." Journal of Personality and Social Psychology, vol. 92, no. 6, 2007, pp. 1087-101, https://doi.org/10.1037/0022-3514.92.6.1087.
In the text: (Kahneman 45); (Duckworth et al. 1090).
What to notice: full first names; title case; article titles in quotation marks and the journal (the "container") in italics; labels "vol.", "no." and "pp."; the date near the end; no comma between the name and the page in the in-text citation, and no year at all. With three or more authors MLA gives only the first, followed by "et al.", in the works-cited list as well. The page range is shortened to the digits that change: 1087-101 means 1087 to 1101.
Chicago 18th edition
Chicago has two systems. In notes and bibliography, the first time you cite a source you write a full footnote, and after that a short one:
1. Daniel Kahneman, Thinking, Fast and Slow (Farrar, Straus and Giroux, 2011), 45. 2. Kahneman, Thinking, Fast and Slow, 45.
The bibliography inverts only the first author and lists everyone up to six:
Duckworth, Angela L., Christopher Peterson, Michael D. Matthews, and Dennis R. Kelly. "Grit: Perseverance and Passion for Long-Term Goals." Journal of Personality and Social Psychology 92, no. 6 (2007): 1087–1101. https://doi.org/10.1037/0022-3514.92.6.1087.
In author-date the reference list moves the year to just after the names, and the text gets (Kahneman 2011, 45): no comma between author and year, unlike APA.
The 18th edition (2024) dropped the place of publication for books, so "New York: Farrar, Straus and Giroux" is now just "Farrar, Straus and Giroux". Many style sheets written before 2024 still show the city; follow your instructor if they ask for it.
Harvard
Harvard is a family of author-date styles rather than one rule book. The most widely used version in the UK is Cite Them Right (13th edition, 2025):
Kahneman, D. (2011) Thinking, fast and slow. Farrar, Straus and Giroux. Duckworth, A.L. et al. (2007) 'Grit: Perseverance and passion for long-term goals', Journal of Personality and Social Psychology, 92(6), pp. 1087–1101. Available at: https://doi.org/10.1037/0022-3514.92.6.1087.
It looks like APA at first glance, but the year has no full stop after it, initials have no spaces, article titles get single quotation marks, and from four authors it writes "et al." even in the reference list.
The same information, three priorities
| APA 7 | MLA 9 | Chicago 18 (N-B) | Harvard (CTR) | |
|---|---|---|---|---|
| Year position | After author | Near the end | Near the end | After author |
| In-text | (Kahneman, 2011, p. 45) | (Kahneman 45) | Footnote | (Kahneman, 2011, p. 45) |
| Title case | Sentence | Title | Title | Sentence |
| Et al. in the list from | Never (21+: first 19, …, last) | 3 authors | 7 authors | 4 authors |
| Et al. in the text from | 3 authors | 3 authors | 3 authors | 4 authors |
Common mistakes
- Mixing styles. The commonest error is an APA reference list with MLA in-text citations, or the reverse. Choose one style and use it for both.
- Copying the title case from the source. Most books print titles in title case on the cover, but APA and Harvard want sentence case in the list. Converting by hand is error-prone because proper nouns must stay capitalised: "Vietnam", "English" and "Bayesian" keep their capitals in sentence case.
- Applying et al. at the wrong count. Three authors become "et al." in the text in APA, MLA and Chicago, but not in Cite Them Right Harvard, which waits until four.
- Writing "pp." in APA in-text citations for a single page. One page is "p. 45", a range is "pp. 45–47".
- Pasting a DOI as "doi:10…". APA, MLA and Chicago all prefer the link form https://doi.org/10…
- Losing the italics. Copying through a plain-text editor removes them. Use a copy that keeps formatting (the tool's Copy button does) and paste straight into your document.
A quick way to get it right
Pick the style your course names, enter what is printed on the source, and let the tool apply the rules: open the citation generator, switch between the styles to see the same source change, and use Add to list to build an alphabetical reference list. If your university publishes its own Harvard guide, compare one entry with it before you copy the whole list, and keep your reading notes and quotes in flashcards so the page numbers are at hand when you write.