Principles of Citing Sources: Understanding Citation Styles

At a Glance

• There are three main styles used at Yale: MLA, APA, and Chicago. 
• Academic disciplines have varying expectations for how to list citation information. In some instances, even two journals in the same field will use different styles. 
• All three of these styles require the same basic information, but the order of that information varies, in part because different academic fields emphasize different elements of a source when referring to previous research.

Understanding Different Citation Formats

MLA and APA Citations

MLA style, defined by the Modern Language Association, is most common in the humanities. Because humanities research highlights how one piece of writing influences another, MLA style emphasizes the author’s name and the page in the original text you’re using. This information allows scholars to track down easily the exact sentences you’re analyzing. 

APA style, defined by the American Psychological Association, is most common in the social sciences. Although the author’s name is an important element in APA citations, this style emphasizes the year the source was published, rather than the page number, which allows a reader to see quickly how the research you’re writing about has evolved over time.

Note: Both MLA & APA citation are “in-text,” which means they put information inside the paragraph, usually in parentheses. Chicago style, defined below, puts citation information into footnotes. The page linked here shows examples of these styles in action. But note that works written with MLA or APA style can also include what are sometimes called discursive footnotes. Discursive footnotes are not primarily source citations, but instead discuss in a sentence or two some aspect of the evidence that is not part of the paper’s main argument. 

Chicago Style Citations

The alternative to in-text citation is to use footnotes, which give source information at the bottom of the page. One common approach to footnotes is called Chicago style, defined by the University of Chicago. Chicago style is especially popular in historical research. When developing a historical explanation from multiple primary sources, using footnotes instead of inserting parenthetical information allows the reader to focus on the evidence instead of being distracted by the publication information about that evidence. The footnotes can be consulted if someone wants to track down your source for further research.