When to Cite Sources

You’ll discover that different academic disciplines have different rules and protocols concerning when and how to cite sources, a practice known as “citation.” For example, some disciplines use footnotes, whereas others use parenthetical in-text citations; some require complete bibliographic information on all works consulted, whereas others require only a list of “Works Cited.” As you decide on a concentration and begin advanced work in your department, you’ll need to learn the particular protocols for your discipline. Near the end of this booklet, you’ll find a brief sampling of commonly used citation styles.

The five basic principles described below apply to all disciplines and should guide your own citation practice. Even more fundamental, however, is this general rule: when in doubt, cite. You’ll certainly never find yourself in trouble if you acknowledge a source when it’s not absolutely necessary; it’s always preferable to err on the side of caution and completeness. Better still, if you’re unsure about whether or not to cite a source, ask your professor or preceptor for guidance before submitting the paper or report.

1. Quotation. Any verbatim use of a source, no matter how large or small the quotation, must be placed in quotation marks or, if longer than three lines, clearly indented beyond the regular margin. The quotation must be accompanied, either within the text or in a footnote, by a precise indication of the source, identifying the author, title, place and date of publication (where relevant), and page numbers. Even if you use only a short phrase, or even one key word, you must use quotation marks in order to set off the borrowed language from your own, and you must cite the source.

2. Paraphrase. Paraphrase is a restatement of another person’s thoughts or ideas in your own words, using your own sentence structure. A paraphrase is normally about the same length as the original. Although you don’t need to use quotation marks when you paraphrase, you absolutely do need to cite the source, either in parentheses or in a footnote. If another author’s idea is particularly well put, quote it verbatim and use quotation marks to distinguish his or her words from your own. Paraphrase your source if you can restate the idea more clearly or simply, or if you want to place the idea in the flow of your own thoughts—though be sure to announce your source in your own text (“Albert Einstein believed that…”) and always include a citation. Paraphrasing does not relieve you of the responsibility to cite your source.

3. Summary. Summary is a concise statement of another person’s thoughts or ideas in your own words. A summary is normally shorter than the original — a distillation of the source’s ideas. When summarizing other people’s ideas, arguments, or conclusions, you must cite your sources — for example, with a footnote at the end of each summary. Taking good notes while doing your research will help you keep straight which ideas belong to which author. Good note-taking habits are especially important when you’re reviewing a series of interpretations or ideas on your subject.

4. Facts, Information, and Data. Often you’ll want to use facts or information to support your own argument. If the information is found exclusively in a particular source, you must clearly acknowledge that source. For example, if you use data from a scientific experiment conducted and reported by a researcher, you must cite your source, probably a scientific journal or a website. Or if you use a piece of information discovered by another scholar in the course of his or her own research, you must cite your source. But if the fact or information is generally well known and accepted—for example, that Woodrow Wilson served as president of both Princeton University and the United States, or that Avogadro’s number is 6.02 x 1023—you do not need to cite a source. Note that facts are different from ideas: facts may not need to be cited, whereas ideas must always be cited. Deciding which facts or pieces of information require citation and which are common knowledge, and thus do not require citation, isn’t always easy. For example, finding the same fact or piece of information in multiple sources doesn’t necessarily mean that it counts as common knowledge. Your best course of action in such a case may be to cite the most credible or authoritative of the multiple sources. Refer to a later section in this booklet, “Not-So-Common Knowledge,” for more discussion of how to determine what counts as common knowledge. But remember: when in doubt, cite.

5. Supplementary Information. Occasionally, especially in a longer research paper, you may not be able to include all of the information or ideas from your research in the body of your own paper. In such cases, insert a note offering supplementary information rather than simply providing basic bibliographic information (author, title, place and date of publication, and page numbers). In such footnotes or endnotes, you might provide additional data to bolster your argument, or briefly present an alternative idea that you found in one of your sources, or even list two or three additional articles on some topic that your reader might find of interest. Such notes demonstrate the breadth and depth of your research, and permit you to include germane, but not essential, information or concepts without interrupting the flow of your own paper.

Additional claims or analysis of your own that you want to include in your essay without distracting readers from the central line of argument may also appear in footnote form. In these cases, the footnote will not include a citation because the ideas or findings presented belong to you.

In all of the cases above, the standards of academic integrity require both citing the source in the text of your essay and its incorporation into your bibliography. To be clear, it is not enough to simply list a source in your bibliography if it deserves explicit citation in the essay’s body. Failure to provide that citation may result in being charged with plagiarism.

Sometimes, though rarely, a source merits inclusion in your bibliography even when it doesn't merit a particular citation in your paper’s text. This most often occurs when a source plays a critical role in your understanding of your topic, but never lends a specific idea or piece of evidence to your essay’s argument. For example, imagine you’re writing a paper about totalitarian regimes, and your thinking about such regimes is heavily influenced by your reading of George Orwell’s 1984. Imagine further that nothing from the novel appears explicitly in your essay, and your strongest reference to the book is describing these regimes as “Orwellian” in passing. Here there would be no need to cite 1984 directly, but it would be appropriate to list it in your bibliography. As always, if you’re unsure about a particular case, err on the side of providing a citation and a bibliography entry.

For international students, it’s especially important to review and understand the citation standards and expectations for institutions of higher learning in the United States. Students who have done their college preparation at schools in other countries may have learned research and paper-writing practices different from those at Princeton. For example, students from schools in East Asia may learn that copying directly from sources, without citation, is the proper way to write papers and do research. Students in France, preparing for the Baccalaureate examination, may be encouraged to memorize whole passages from secondary sources and copy them into papers and exam essays. Those cultural differences can sometimes lead to false assumptions about citation practices and expectations at Princeton. Make sure you understand the University’s academic regulations and ask for assistance from your professors or preceptors if you’re not sure.

The Writing Center, located in Whitman College, is also a key resource for students wanting to learn more about proper note-taking and citation practices. To make an appointment, visit <www.princeton.edu/writing/appt> or drop in without an appointment Sunday through Thursday evenings.