Guidelines on the Use of External Sources

Rod Howell
Dept. of Computing and Information Sciences
Kansas State University
Manhattan, KS 66506

Writing is an important component of any university curriculum. Often a student's writing uses ideas or words originating from others. The extent to which this use of external sources is allowed or required varies greatly depending upon the purpose of the assignment or paper. Therefore, we do not attempt to address this issue here. Instead, we focus on how plagiarism can be avoided when external sources are used.


The American Heritage Dictionary[1] gives the following definitions of plagiarize:
  1. To steal and use (the ideas or writings of another) as one's own.
  2. To appropriate passages or ideas from (another) and use them as one's own: "I did hate to be accused of plagiarizing Bret Harte." (Mark Twain).
Plagiarism is an unacceptable practice in our society. Its practice can result in both academic and legal penalties. Specific academic penalties at KSU range from a 0 on the assignment in which it occurs to dismissal from the University.

The guiding principle in avoiding plagiarism is summarized as follows:

Always give credit to those whose writings or ideas you use.

Using the Writings of Others

Writing is a creative activity. Thus, the expression of ideas, apart from the ideas themselves, is typically a result of both creative thinking and much revision. Just as you deserve credit when you spend time and energy expressing ideas in writing, others also deserve credit when you incorporate their writing into yours. Furthermore, you do not deserve credit for what someone else wrote, even if there is good reason to include it in your writing.

Because writing is a creative activity, it is best to avoid using the writing of others unless there is a good reason for doing so. If we write a paper that consists mainly of the writings of others, we have probably contributed very little creativity of our own.

There can be, however, good reasons for including the writings of others in our writing. Consider, for example, the quotation from The American Heritage Dictionary above. We wanted to give a widely-accepted definition of the word, "plagiarize". The authoritative references for widely-accepted definitions are dictionaries. Had we simply paraphrased the definition, a skeptic might conclude that we were redefining the word to suit some hidden agenda. Thus, the attribution of the definition serves two purposes: not only does it give credit to those who originally expressed the definition, it also lends credibility to the claim that this is, in fact, the commonly accepted definition.

When there is good reason for including the writings of others in our writing, this can be done in one of two ways. When the included writing is short (e.g., the quote from Mark Twain in the definition of "plagiarize" above), it can be enclosed in quotation marks. If the included writing is longer (e.g., the definition of "plagiarize" above), it should be set apart from the enclosing text in a way that clearly shows its beginning and end.

There are some instances in which a quotation may be changed slightly when it is reproduced. For example, it may be appropriate to include a definition or theorem from an external source in which different notation was used. Thus, in order to make the definition consisitent with the notation in our paper, we may need to make superficial changes to it. In Computer Science, we typically do this without comment. Thus, if we say, "Tarjan gives the following definition in [...]:", it will be understood that our quotation may contain some superficial differences from the exact words originally used by Tarjan.

The manner in which credit is given to the original authors varies depending on the discipline and the style guidelines of publications in which the work may be published. In Computer Science, it is common practice to include a reference label within square brackets in the text, and to list at the end of the paper detailed designations of the sources of the quotations. The details in the reference list typically include the title, authors, and date, as well as sufficient information to enable readers to find the source for themselves if the work is publicly accessible. The inclusion of the reference label within the text itself serves to identify the source of the specific quotation, so that it is clear which quotation comes from which source. The reference label for the quotation from The American Heritage Dictionary above is "[1]".

Using the Ideas of Others

Using the ideas of others is essential to academic research. Ideas are distinct from the expression of the ideas in writing. For example, in 1931, Gödel showed that any logical system powerful enough to express number-theoretic statements involving addition and multiplication must be capable of expressing statements which can be neither proved nor disproved within that system [2]. Notice that we have just summarized the essence of Gödel's idea without using his words (or even a translation of his words from German to English). Over the past 70 years, many results in Mathematics and Computer Science have been built upon Gödel's fundamental result. When these subsequent results were presented, it was proper for the authors to give Gödel credit for the fundamental idea upon which their subsequent ideas were built.

Usually, when we are expressing our own ideas, it is unnecessary to reproduce the writings of others. Rather, it is usually sufficient to provide our own expression to the ideas upon which our ideas depend. When such expression is sufficient, the reproduction of the original writings that express these ideas is laziness.

In order to be able to provide our own creative expression of the ideas of others, it is essential that we first try to understand these ideas, because the better our understanding of an idea, the better equipped we are to express the idea. Having an adequate understanding of an idea, we should be able to express it in our own words without having the author's original words in front of us. Expressing an idea in this way helps us to avoid such superficial rephrasing as replacing some of the author's original words with synonyms. Such rephrasing is actually a form of plagiarism, because it is essentially using the original author's creative expression without giving proper credit for that expression.

As is the case when we use the writings of others, we need to give appropriate credit when we use the ideas of others. The notation we use should be the same as that used when we quote others. It is essential that the reference labels be included in the text in such a way that it is clear which ideas are our own and which ideas come from others.


[1] The American Heritage Dictionary of the English Language, William Morris, Editor, Houghton Mifflin, 1976.

[2] K. Gödel, "Uber formal unentscheidbare satze der Principia Mathematica und verwander systeme", Monatschefte fur Mathematik und Physik 38 (1931), pp. 173-198.

Copyright © 2002, Rod Howell. All rights reserved.

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