Sources: About Citing Sources: When to Cite Sources

Table of contents

About citing sources

Why acknowledge sources?

When to cite sources

What is plagiarism?

ALTHOUGH SCHOLARS in various disciplines may differ on the particulars of when to cite and when not to cite sources, you should always cite in the following cases.

Cite sources for all verbatim quotations of two or more consecutive words.

Readers expect to know the original source of any quotation, whether for the purpose of checking its accuracy or using it in their own work. Exact wording, or even a single distinctive word, taken from a source should be placed in quotation marks.

Cite sources from which you paraphrase or summarize facts or ideas.

Whenever you rely on another's information or ideas, you should cite your source, even if you do not use a verbatim quotation. When you paraphrase a source in your work, be sure to organize this summary or paraphrase in your own distinctive manner; mold it into the flow of your argument and use your own words and sentences. If you do make use of even part of a sentence, be sure to use quotation marks. Seeming to paraphrase when you are in fact quoting is considered plagiarism.

Cite sources for ideas or information that could be regarded as common knowledge but which you think your reader might still find unfamiliar.

This case addresses those situations where no definitive boundary exists between an idea that has not originated with you but which seems generally well-known (such as the heliocentric theory of the solar system), and a well-known idea you intend to interrogate pointedly or to treat as a distinctive or seldom well-understood concept (Freud's notion of the Oedipus complex, for example). When you refer to a well-known idea (e.g., heliocentrism), you do not need to provide a citation indicating its source, although when you first mention this idea you should specify your own understanding of it. When you make special, sustained use of a well-known idea (e.g., Oedipus complex), however, you do need to provide a citation.
In general you need not cite the source of information that seems part of our common stock of knowledge. For example, you can assume that your readers know that the atomic structure of water is H₂O; that Jane Austen wrote Pride and Prejudice; that Martin Luther King, Jr. was a leading figure in the U.S. civil rights movement; or that Charles Darwin claimed that new species of plants and animals evolve over long periods of time. Citing references for such facts is unnecessary.
You do need to cite specific sources for information that you judge your readers might find unfamiliar: for example, that water comprises 55 to 65 percent of female bodies; ¹ that Pride and Prejudice, unlike many English novels written in the years following the French Revolution, endorses pleasure and happiness; ² that the FBI regularly placed Martin Luther King's private life under surveillance; ³ or that Darwin seems to have been an undistinguished student at Edinburgh. ⁴
Whenever you encounter a borderline situation where you cannot decide whether to cite a source, take the safest course: assume your reader isn't necessarily a scholarly expert on the subject of your work and cite the source.

Cite sources that add relevant information to the particular topic or argument of your work.

The first three cases apply to most undergraduate essay assignments. For more extensive research projects like honors theses or seminar papers, you may wish to employ supplementary or discursive citations to include further information on your subject, either to express different views on it which your work does not explicitly entertain, or simply to help your reader pursue a related interest. ⁵
Supplementary citations require the format of notes. Even if you are employing the parenthetical or author-date format for the citations in your paper, supplementary citations are always formatted as notes. You usually introduce such a note by writing "See also," followed by bibliographical information in the style you are using for your paper. Exercise restraint, however, in using supplementary footnotes; too many can distract readers from the flow of your main argument.

Cite sources for materials that you might not normally consider as "texts" because they are not written.

Depending on the discipline, your sources might include materials such as public lectures, architecture, laboratory procedures, musical compositions, films, audio or visual tapes, works of art, maps, Web pages, statistical tables, or electronic databases. If used as in the cases listed above, any non-written source also must be cited.
When doing a joint lab experiment for a science course, you should record in your notebook the names of your co-workers and their precise activity in performing the experiment. Or when doing laboratory work that relies on an innovative method originated by another scientist, you should cite in your lab report the source of this method just as if it were a quotation or paraphrase from a written text — unless, that is, this method was an explicit aspect of the course's assignment or required materials.

Cite sources for non-interchangeable computer programs and software.

Scholars in the sciences and social sciences frequently use computer software programs for numerical calculation, data analysis and presentation. Computer applications that are interchangeable and thereby help any user achieve similar results do not need to be cited. Such applications include:

•	Word-processing programs
•	Spreadsheet programs
•	Database programs
•	Draw programs

Computer applications with unique features that influence the results of a calculation or analysis should be cited, along with the technique used with the program to obtain the result described in your paper. Such applications might include:

•	Geographic Information Systems (GIS) programs
•	Computer algebra programs
•	Data analysis programs
•	Calculation programs
•	Three-dimensional visualization software

When writing programs in the computer sciences, in your code you should include citations for:

•	your direct use of someone else's computer program or part of that program in your work;
•	your use of non-standard data manipulation or graphing programs;
•	your use or modification of an existing but perhaps not commonly known algorithm.

Consult your professor for advice on when to cite in artistic works.

Questions may arise about whether citations are required for sources variously used in projects involving creative writing, musical composition, film-making, drama, painting, drawing or other creative media. Always discuss such cases with your professor.

If in doubt about whether or not to cite a source, cite.

1	Jane Brody, Jane Brody's Nutrition Book (New York: Norton, 1981) 219.
2	Claudia L. Johnson, Jane Austen: Women, Politics, and the Novel (Chicago: U of Chicago P, 1988) 78.
3	David J. Garrow, Bearing the Cross: Martin Luther King, Jr., and the Southern Christian Leadership Conference (New York: Morrow, 1986) 361.
4	Adrian Desmond and James Moore, Darwin (London: Joseph, 1991) 27.
5	For a delightful history of citation practices, see Grafton. This, by the way, is a supplementary citation.