Citing a Reference Again
The use of ibidem -- shortened to ibid. -- means that a source cited is found "in the same place" as that cited in the subsequent refernce. This can only be used when referring to the same exact source immediately preceding it. It can be used when the page numbers differ or other parts differ but only if the source is otherwise the same.
Once a reference has been cited, subsequent citations should use a shortened form. This should be done in two ways. If the reference immediately follows the same reference then it should be cited as Ibid. followed by any change in the page number. If the reference is cited again but not immediately, then it should be done in a shortened form.
Example:
4. C. Wright Mills, Power, Politics, and People: The Collected Essays of C. Wright Mills (New York: Oxford University Press, 1963), 406.
5. Ibid.
6. Ibid., 84-87.
7. Goodwyn, Populist Moment, 88.
8. Ibid., 150.
9. Mills, Power, Politics, and People, 405.
10. Ibid., 406; Goodwyn, Populist Moment, 89.
Note: An Ibid. can only be used after footnote 10 (which has multiple sources) in this example if footnote 11 is exactly the same. Otherwise it would have to cite in short form:
11. Mills, Power, Politics, and People, 404; Goodwyn, Populist Moment, 90.