A citation serves as an acknowledgment of the source you're using. You need of course to cite a source whenever you use its exact words, but you also need to cite when you use its idea, information, data, organizational structure, or key concept, even if you put it in your own words. You don't need to cite a source when the material is common knowledge - knowledge that is generally accepted, widely available, and not subject to interpretation. The dates of the Civil War are common knowledge; its causes are not. Different things may count as common knowledge in different fields; if you're not sure, you should cite your source.
The links below give more details on when you need to cite, along with examples of proper and improper citation and paraphrase. See also Gordon Harvey's Writing with Sources (Indianapolis: Hackett, 1998), pp. 14-15.
- Quoting, Paraphrasing, and Summarizing (Purdue OWL)
- Sources and Citation (Dartmouth College)
- Writing with Internet Sources: A Guide for Harvard Students
- The Harvard Guide to Using Sources
Mechanics of Citation: After you've figured out how to incorporate a source into your essay, you need to think about the technical aspects of the citation. The first thing to determine is the style of citation you’re using. Different disciplines tend to prefer different styles; for instance, English departments often use MLA style, while History departments might use Chicago style. If you’re not sure what style you should be using, ask your professor. The next thing to determine is the type of document you’re citing. You’ll need to include different information depending on whether you’re citing a book, article, newspaper, film, interview, etc. There are also rules for citing electronic sources such as websites and email.
Citation Guidelines for MLA, Chicago, APA, and CSE Styles: The chart below indicates the major types of citation style. The links will take you to the relevant pages of Purdue’s Online Writing Lab, Williams College Libraries, and Penn State Libraries. These sites have useful pull-down menus that will tell you how to write the bibliographical entry for every possible kind of source, from books and articles to paintings, listserv postings, and newspaper articles. Another good resource is UW-Madison'sCiting References in Your Paper, which also indicates the proper format for the various kinds of citation. You might also try an online bibliography generator such as bibme, but if you use this type of website be sure to double check that your sources are cited fully and properly.
| Name | Disciplines | In-text Citations | Bibliography | Sample Paper |
|---|---|---|---|---|
| MLA (Modern Language Association | English and other humanities | MLA in-text citations | MLA works cited | MLA sample paper |
| Chicago | History and other humanities | Chicago Author-Date | Chicago Notes and Bibliography | Chicago sample paper |
| APA (American Psychological Association) | Social sciences and natural sciences | APA in-text citations | APA reference list | APA sample paper |
| ACS (American Chemical Society) | Chemistry | ACS in-text citations | ACS reference list |