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Any idea or fact that was not an original thought out of your head must be cited.

Why We Cite

Citations serve many functions.

  • A citation lets the reader know that an idea came from someone other than you
  • A citation from an expert source lends authority to your argument
  • A citation tells the reader where to go to find out more about the idea.

Here's your basic principle for citations:

1. Whenever you quote something from another source, you must cite it.

2. Whenever you refer to or describe or summarize an idea you found in someone else’s work, you must cite it.

For example: If you read in a book that Godzilla killed a million people, whereas you found in another book that Napoleon only killed half a million people, you could use these two facts together in support of your argument that Napoleon was less harmful than Godzilla. You would need to cite both sources:

Napoleon may have caused the deaths of half a million people,¹ but Godzilla

caused twice as many.² The general’s destructive power is clearly no match

for that of the rampaging monster.

¹John Doe, Stuff that Napoleon Did, 324th edition (New York: Fictitious
Publishers, 1932), 471.
²Fred Flintstone, Godzilla Was Not My Grandfather (Bedrock: Dodo Bird Press,
10,000 BCE), 12.

In other words, even when you are not directly quoting your source, you still must cite it.

Where We Cite

There are two places where your sources get cited. They each serve a different purpose.

  • In the bibliography. The bibliography is a list of all the sources you used. Each source is listed once.
  • In footnotes. A footnote says where in a book or article information can be found. Footnotes have page numbers.

These are separate things. Do not make your footnotes just references to numbered bibliography items Think of your footnotes as pointing to your bibliography. Like so:


The first footnote in this illustration says:

You can find this information on page 34 of the book listed under
“Smith” in my Bibliography.

How We Cite

You should consult a fuller reference on citations; the one used here is:

University of Chicago Press. The Chicago Manual of Style, 15th ed.
Chicago: U. of Chicago Press, 2003.

Here you see the information needed for anyone to find the work being cited:

  1. The author [normally a person, of course, but in this case, an organization];
  2. The title;
  3. Version or edition;
  4. Location and name of publisher;
  5. Copyright or publication date.

This is the bibliography entry. The footnote entry is formatted slightly differently. Because a footnote is used to point to a specific idea expressed in a specific place in a work, it usually contains a page number.


The following styles are derived directly from The Chicago Manual of Style (15th ed.), accessible online at http://chicagomanualofstyle.org. They have a quick guide for common kinds of citations.

  • All sources you use must appear (once) in the Bibliography. The publication information and year are important in that they both help establish the reliability of the work and make it easier to find the work should the reader want to find out more.
  • All facts, quotes, paraphrases, and ideas from your sources used in your paper must be cited with either footnotes or in-text citations.


Suppose you’re writing about how the Aztecs were very different from the Spaniards that conquered them, and on page 65 of a book called Stuff About the Aztecs by Fred Smith you find information that’s helps you support that argument: that the Aztecs painted their legs blue on Arbor Day. You can use that information either by direct quote, or just by paraphrasing it:

   The Aztecs’ daily lives were unlike those of the Spaniards. For

example, the Aztec practice of painting their legs blue on Arbor Day was

unlike anything the Spaniards had ever encountered.¹ In fact it has been

said that “the Aztecs were inordinately fond of the color blue, and

please don’t take any of this seriously as it’s just joke examples.”²

¹Smith, 65.
²Truman, 379.

The first footnote points to page 65 of the book listed under “Smith” in your Bibliography. Likewise, the second footnote, for the direct quote, points to page 479 of a journal listed under Truman in the Bibliography.


Smith, Joseph. Stuff About the Aztecs. Berkeley, CA: U. of California
Press, 2008.

Truman, Robert C. “This Is a Journal Article About the Aztecs.” Journal
of Historical Journal Articles
34 (1997): 347–400.

The format for the journal article citation is slightly different. You include the article title, the journal name, the volume number, the year, and the pages covered by the entire article.